China Product
History
Early Years
Martin Stf was born 13 November 13, 1978 in Varberg on the Swedish West Coast. He started playing the piano at a tender age and did classical piano concerts between the age of 6-8. Stf started experimenting with synthesizers in the mid 80s, which ushered in a whole new frontier of musical experiments and explorations. He abandoned the classical music world and spent the next ten years producing his own material. Stf states: never thought about releasing any of my music until I was 17. Then, all of a sudden, it was time to get a job and I realized that there was nothing else I wanted to do at that time than making music.3] biodegradable food packaging
Early Career: Late 1990s sausage casings
"Lotus" sausage casing
File:Lotus.ogg
The song "Lotus" from the album "The Intergalactic Slapstick"
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"Soundboy Killa"
File:SoundboyKilla.ogg
The song "Lotus" from the album "The Intergalactic Slapstick"
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"Exfoliant"
File:Exfoliant.ogg
The song "Exfoliant" from the Ep "Dead Or Alive"
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Martin Stf worked in the commercial studio Bohus Sound Recordings 1997-1999 and engineered/produced various jazz and rock bands. During this time he also made a song for the Euro-Vision contest.
In1997 Martin Stf formed the outfit Necton together with Patrik Olsn, mainly focusing on progressive and psychedelic trance. Necton released two full length albums, 6 vinyl Eps, and were featured on numerous CD compilations. They were signed to Spirit Zone Recordings, Digital Structures and Spiral Trax. Necton toured extensively around the world between 1997 -2003.
During this time, Martin Stf released Nu Skool Breaks on labels Ministry Of Sound, Sound Of Habib, Muti Music, Random Recordings, Hope Recordings, and Muve Recordings under the alias Rhoca. Stf also released funky Techno on Iboga Records, Plusquam Records, and Nanobeat Records.
The Liquid Stranger Project: 20032009
Martin Stf launched the Liquid Stranger project in 2003. His intention was to have one alias that would encompass all his musical output. Consequently, he has produced a wide variety of music under the name Liquid Stranger. At first, Stf's plan was to keep his identity a secret. He never did interviews or showed his face on stage. Stf states: fter a while it became quite tricky. in fact, Interchill finally ruined this idea by writing my name on the record sleeves.5] Liquid Stranger's creative output ranges from suggestive Ambient soundscapes to movie scores, pop, dub, infernalia, drill n bass, and electronica.
The first release under the name Liquid Stranger was the song Environmental Meltdown, featured on the compilation Global Psychedelic Chill Out - Compilation Vol. 4 by Spirit Zone Recordings.
When asked in an interview why he moved away from the trance scene, Stf replied: never really switched per se, I have always made tons of different types of music. During the time I toured with Necton, I produced various stuff like Ambient, Electro and Drill n bass. What excites me is the fusing of genres. I have no fixed style that I stay with too long, I do not like boundaries.7]
Subnatura Collective
In 2003, Martin Stf founded the musical collective Subnatura together with Marckus Andersson. Subnatura released 12 digital Ep's and were featured on net label Monotonik and the video DVD Collectanea: First Course, released by Escapi Music.
Candy Mind Records
Cover art for the album Anywhere And Me
In 2004, Martin Stf founded the record label Candy Mind Records together with his brother Jens Stf. Candy Mind Records released 33 digital Ep's, and one full-length CD release from Dorothy's Magic Bag. During the Candy Mind era, Martin Stf and his brother started the duo Hectopascal. They released the full-length album Anywhere And Me on Kahvi records. The Ep's Pixels and Pixies, and Alive In Veddige were released on Candy Mind Records.
Interchill Records
In 2005, Stf got signed to Canadian label Interchill Records. The song Political Finga was featured on Earth Octave Lounge Vol. 2, and received high praise from the dub community. The song Liquid Stranger On The Run appeared on the compilation Dissolving Clouds and got frequent plays on underground radio. Rick Anderson of Allmusic wrote about Liquid Stranger s someone who has previously worked in progressive rock, punk, techno, breakbeat, and IDM genres, Staaf brings a certain sophistication to his Interchill-style dubtronica, and there is lots to hear for those who take the trouble to listen closely: the brass and orchestral samples bubbling beneath the surface of the gently churning dub of Liquid Stranger on the Run.11]
The song We Meet At Last appeared on the compilation Bliminal, and was licensed by Velcrow Ripper for the film Fierce Light Where Spirit Meets Action, released in 2008.
The Invisible Conquest
Cover art for the Album The Invisible Conquest
The first full-length Liquid Stranger album, The Invisible Conquest, was released by Interchill Records in 2007. A bass-heavy album with melodic bass lines, percussive grooves, tribal accents and minimal psychedelic overlays. The Invisible Conquest received high ratings and praise from critics. Properly Chilled wrote of the album iquid Stranger's sound has the grandeur of its peers without building an humongous ego. . .we give this record two thumbs way up and a standing ovation12], and Raves.com described it as taste of the experimental, a chunk of tribal, all wrapped around a root of dub excellence. . .dub vibes that shoot right through to the middle of your gut.13] Morpeus Music describes the music of Liquid Stranger as ass driven atmospheric chillout. Liquid Stranger creates mostly instrumental montages with strong rhythmic content.14]
The Intergalactic Slapstick
Cover art for the Album The Intergalactic Slapstick
The second full-length Liquid Stranger album was released by Interchill Records in 2009. This album saw Liquid Stranger moving significantly into heavier Dubstep and reggae influenced grooves. Vocalists Brother Culture, Danman, Deeyah and Warrior Queen are featured on the album. Seb Taylor from Kaya Project plays Steel Guitar on the songs His Fully Automatic Wheelbarrow, and Dew Point. Dub-connection wrote of the album he production varies and waves between a electro-dub chill-out and powerful tracks in the limit of drum and bass with a bit of stepper to spice the sound.15] Morpheus Music wrote of the album he diverse roots of Liquid Stranger's sound sprawl across electro, ambient, grime, global, breaks and garage.16] Sun is shining wrote ome albums float your boat with one or two tracks becoming ingrained in your mind for days, weeks and even months. Once in a blue moon an album levitates that boat out of the water and into the clouds. LS long awaited second album is certainly filed in the latter category.17]
Background Information
Influences
Martin Stf mentioned in an interview on BBC radio that his main influence comes from music from vintage computer games. In an interview with Chillbase, Stf says that he does not listen to music all that much, except when he is on a concert. In the same interview Stf explains that he gets inspiration from movie soundtracks, dreams, and everyday life.
Discography
Albums
Anywhere And Me (2005)
The Invisible Conquest (2007)
The Intergalactic Slapstick (2009)
Singles
It Came From The Dessert (2003)
Subsonic Soil (2004)
Pixies And Pixels (2004)
Dead Or Alive (2005)
Spores (2005)
Alive In Veddige (2005)
Banana(Electro)Split (2006)
Monster (2009)
Steel Trap (2009)
Tracks Appear On
Collectanea First Course - "Impossible Mission" (2003)
Global Psychedelic Chill Out Vol. 4 - "Environmental Meltdown" (2003)
Subnatural Soundscapes Vol I - "From The Sky" (2003)
Purple Pollen - "Bismarch" (2004)
Some Candy Before Christmas - "Ginger Bread Juice" (2004)
Sound Of Subnatura - "Onda gat" (2004)
Burning Chocolate - " Den Infekterade Terminalen" (2005)
Dissolving Clouds - "Liquid Stranger On The Run" (2005)
Earth Octave Lounge Vol. 2 - "Political Finga" (2005)
Promotion CD 2005 - "Velour, Bleck" (2005)
Electromeister 1.0 - "Smeartest" (2006)
Masters Of The Green Insects - "Jakten P Guldpokalerna" (2006)
New World Dub 01 - "Political Finga" (2006)
A Beginning Of An End - "I And I" (2007)
Bliminal - "We Meet At Last" (2007)
Amenorea Dubs (Volume 01) - "Zenmaniax" (2008)
One Dub - "Welcome To My Culvert" (2009)
Remixes
"Slem - Denri (Liquid Stranger Remix)" (2004)
"Dorothy's Magic Bag - Ghostmachine (Liquid Stranger Laxative Remix)" (2004)
"Hectopascal - Svlj Din Saliv (Liquid Stranger Remix)" (2004)
"Goto80 - Wombatman (Liquid Stranger's Duplomix)(2005)"
"Bruno Ferrari - Jean Gabin (Liquid Stranger's Duplomix)" (2005)
"Dorothy's Magic Bag - Monster (Liquid Stranger Remix)" (2006)
"Bombay Dub Orchestra - Journey (Liquid Stranger's Sliptrip Edit)" (2009)
"Goto80 - Breakfast (Liquid Stranger's Gourmet Mixture)"(2009)
Releases on
Adversion Recordings
Amenorea
Bleep Street
Candy Mind Records
Escapi
Flexible
Interchill Records
Kahvi Collective
Monotonik
Six Degrees
Sonic Walker
Spirit Zone Recordings
Subnatura
System Recordings
References
^ Koreman, Vincent (2009-10-19). "New Liquid Stranger Dubs". Generation Bass (Triple Trouble Media). http://generationbass.com/2009/10/19/new-liquid-stranger-dubs. Retrieved 2009-11-12.
^ a b Martin, Woods (2009-10-22). "Liquid Stranger Interview". Chillbase (Om media). http://chillbase.org/interviews/172-liquid-stranger-interview. Retrieved 2009-11-10.
^ a b Collins, Andrew Ross (2009-10-15). "In depth with Liquid Stranger". Andrew Ross Collins. Mariko Music Publishing. http://www.interchill.com. Retrieved 2009-11-04.
^ "Martin Stf". Discogs. Discogs. http://www.discogs.com/artist/Martin+Stf. Retrieved 2009-11-11.
^ Collins, Andrew (2009-10-15). "In depth with Liquid Stranger". Interchill Records (Mariko Music Publishing). http://www.interchill.com. Retrieved 2009-11-05.
^ "Liquid Stranger". Discogs. Discogs. http://www.discogs.com/artist/Liquid+Stranger. Retrieved 2009-11-12.
^ "Mindstream 01 - The Boom Radio Podcast by Liquid Stranger". Boom Festival (Boom Festival). 2009-05-03. http://www.boomfestival.org/boom2009/index.php?option=com_content&view=article&id=143:mindstream-01-the-boom-radio-podcast-by-liquid-stranger&catid=50:boom-radio-podcasts&Itemid=122. Retrieved 2009-11-09.
^ "Subnatura". Discogs. Discogs. http://www.discogs.com/label/Subnatura. Retrieved 2009-11-12.
^ "Candymind". Internet Archive. Internet Archive. http://www.archive.org/details/candymind. Retrieved 2009-11-12.
^ "Hectopascal". Discogs. Discogs. http://www.discogs.com/artist/Hectopascal. Retrieved 2009-11-12.
^ Anderson, Rick. "Review". Allmusic. All Media Guide. http://www.allmusic.com/cg/amg.dll?p=amg&sql=10:0xfqxzehld6e. Retrieved 2009-11-09.
^ Gomes, Helder. "Review". Properly Chilled. Properly Chilled. http://www.properlychilled.com/music/release/643. Retrieved 2009-11-10.
^ Upjohn, Kristofer. "Review". Raves.com. Raves.com. http://www.raves.com/cdreviews/show/480/LIQUIDSTRANGER-THEINVISIBLECONQUEST. Retrieved 2009-11-10.
^ "Liquid Stranger - The Invisible Conquest". Morpeus Music. Electronic Music Mall. http://www.electronicmusicmall.com/Html/reviews55.htm. Retrieved 2009-11-11.
^ Chambon, Laurent. "The Intergalactic Slapstick by Liquid Stranger". Dub Connection. Dub Connection. http://dub-connection.net/blog/index.php?post/2009/11/02/The-Intergalactic-Slapstick-by-Liquid-Stranger. Retrieved 2009-11-10.
^ "Liquid Stranger - The Intergalactic Slapstick". Morpeus Music. Electronic Music Mall. http://www.electronicmusicmall.com/Html/reviews79.htm. Retrieved 2009-11-11.
^ "October Release Reviews". Sun Is Shining. Sun Is Shining. http://sunisshiningdubnchill.blogspot.com/2009/10/new-october-release-reviews.html. Retrieved 2009-11-12.
^ "World Odyssey Mix". Pathaan. BBC. 2009-10-25. http://www.bbc.co.uk/asiannetwork/pathaansmusicalrickshaw. Retrieved 2009-10-25.
External links
Liquid Stranger discography at Discogs.
Liquid Stranger artist page at Myspace.
Categories: 1978 births | Ambient musicians | Electronic musicians | Swedish electronic musicians | Swedish musicians | Techno musicians | Dub musicians | Dubstep musicians | Living people | People from Varberg | Remixers | Interchill Records artistsHidden categories: Orphaned articles from February 2010 | All orphaned articles
Friday, April 23, 2010
Liquid Stranger
Passive house
China Product
History
Prof. Bo Adamson, co-originator of the concept
professional hairdryer
Dr Feist, founder of the Passivhaus Institut and co-originator of the concept blow dryer holder
The Passive House standard originated from a conversation in May 1988 between Professors Bo Adamson of Lund University, Sweden, and Wolfgang Feist of the Institut fr Wohnen und Umwelt (Institute for Housing and the Environment ). Their concept was developed through a number of research projects , aided by financial assistance from the German state of Hesse. The eventual building of four row houses (also known as terraced houses or town homes) was designed for four private clients by architects professor Bott, Ridder and Westermeyer. chi hair dryers
The first Passivhaus buildings were built in Darmstadt, Germany, in 1990, and occupied the following year. In September 1996 the Passivhaus-Institut was founded in Darmstadt to promote and control the standard. Since then, thousands of Passive Houses have been built, to an estimate of 15,000 currently. most of them in Germany and Austria, with others in various countries worldwide.
After the concept had been validated at Darmstadt, with space heating 90% less than required for a standard new building of the time, the 'Economical Passive Houses Working Group' was created in 1996. This developed the planning package and initiated the production of the novel components that had been used, notably the windows and the high-efficiency ventilation systems. Meanwhile further passive houses were built in Stuttgart (1993), Naumburg, Hesse, Wiesbaden, and Cologne (1997) .
The products developed for the Passivhaus were further commercialised during and following the European Union sponsored CEPHEUS project, which proved the concept in 5 European countries over the winter of 2000-2001.
In North America the first Passivhaus was built in Urbana, Illinois in 2003, and the first to be certified was built near Bemidji, Minnesota in Waldsee, the German camp of the Concordia Language Villages in 2006.
The world's first standardised pre-fabricated passive house was built in Ireland in 2005 by Scandinavian Homes, a Swedish company that has since also built passive houses in England and Poland.
Standard
The dark colours on this thermogram of a Passive house (right) show how little heat is escaping compared to a traditional building (left).
While some techniques and technologies were specifically developed for the Passive House standard, others (such as superinsulation) were already in existence, and the concept of passive solar building design dates back to antiquity. There was also experience from other low-energy building standards, notably the German Niedrigenergiehaus (low-energy house) standard, as well as from buildings constructed to the demanding energy codes of Sweden and Denmark.
The Passivhaus standard for central Europe requires that the building fulfills the following requirements:
The building must be designed to have an annual heating demand as calculated with the Passivhaus Planning Package of not more than 15 kWh/m per year (4746 btu/ft per year) in heating and 15 kWh/m per year cooling energy OR to be designed with a peak heat load of 10W/m
Total primary energy (source energy for electricity and etc.) consumption (primary energy for heating, hot water and electricity) must not be more than 120 kWh/m per year (3.79 104 btu/ft per year)
The building must not leak more air than 0.6 times the house volume per hour (n50 0.6 / hour) at 50 Pa (N/m) as tested by a blower door,
Recommended:
Further, the specific heat load for the heating source at design temperature is recommended, but not required, to be less than 10 W/m (3.17 btu/ft per hour).
These standards are much higher than houses built to most normal building codes. For comparisons, see the international comparisons section below.
National partners within the 'consortium for the Promotion of European Passive Houses' are thought to have some flexibility to adapt these limits locally.
Space heating requirement
By achieving the Passivhaus standards, qualified buildings are able to dispense with conventional heating systems. While this is an underlying objective of the Passivhaus standard, some type of heating will still be required and most Passivhaus buildings do include a system to provide supplemental space heating. This is normally distributed through the low-volume heat recovery ventilation system that is required to maintain air quality, rather than by a conventional hydronic or high-volume forced-air heating system, as described in the space heating section below.
Construction costs
In Passivhaus buildings, the cost savings from dispensing with the conventional heating system can be used to fund the upgrade of the building envelope and the heat recovery ventilation system. With careful design and increasing competition in the supply of the specifically designed Passivhaus building products, in Germany it is now possible to construct buildings for the same cost as those built to normal German building standards, as was done with the Passivhaus apartments at Vauban, Freiburg. On average, however, passive houses are still up to 14% more expensive upfront than conventional buildings.
Evaluations have indicated that while it is technically possible, the costs of meeting the Passivhaus standard increase significantly when building in Northern Europe above 60 latitude. European cities at approximately 60 include Helsinki in Finland and Bergen in Norway. London is at 51; Moscow is at 55.
These facts have led a number of architects to construct buildings that use the ground under the building for massive heat storage to shift heat production from the winter to the summer. Some buildings can also shift cooling from the summer to the winter. At least one designer uses a passive thermosiphon carrying only air, so the process can be accomplished without expensive, unreliable machinery. (See also Annualized geo solar)
Design and construction
The passivhaus uses a combination of low-energy building techniques and technologies.
Achieving the major decrease in heating energy consumption required by the standard involves a shift in approach to building design and construction. Design is carried out with the aid of the 'Passivhaus Planning Package' (PHPP) , and uses specifically designed computer simulations.
To achieve the standards, a number of techniques and technologies are used in combination:
Passive solar design
Following passive solar building design techniques, where possible buildings are compact in shape to reduce their surface area, with windows oriented towards the equator (south in the northern hemisphere and north in the southern hemisphere) to maximize passive solar gain. However, the use of solar gain is secondary to minimizing the overall energy requirements.
Passive houses can be constructed from dense or lightweight materials, but some internal thermal mass is normally incorporated to reduce summer peak temperatures, maintain stable winter temperatures, and prevent possible over-heating in spring or autumn before normal solar shading becomes effective.
Superinsulation
Passivhaus buildings employ superinsulation to significantly reduce the heat transfer through the walls, roof and floor compared to conventional buildings. A wide range of thermal insulation materials can be used to provide the required high R-values (low U-values, typically in the 0.10 to 0.15 W/(m.K) range). Special attention is given to eliminating thermal bridges.
A disadvantage resulting from the thickness of wall insulation required is that, unless the external dimensions of the building can be enlarged to compensate, the internal floor area of the building may be less compared to traditional construction.
In Sweden, to achieve passive house standards, the insulation thickness would be 335 mm (about 13 in) (0.10 W/(m.K)) and the roof 500 mm (about 20 in) (U-value 0.066 W/(m.K)).
Advanced window technology
Typical Passivhaus windows
To meet the requirements of the Passivhaus standard, windows are manufactured with exceptionally high R-values (low U-values, typically 0.85 to 0.70 W/(m.K) for the entire window including the frame). These normally combine triple-pane insulated glazing (with a good solar heat-gain coefficient, low-emissivity coatings, argon or krypton gas fill, and 'warm edge' insulating glass spacers) with air-seals and specially developed thermally-broken window frames.
In Central Europe, for unobstructed south-facing Passivhaus windows, the heat gains from the sun are, on average, greater than the heat losses, even in mid-winter.
Airtightness
Building envelopes under the Passivhaus standard are required to be extremely airtight compared to conventional construction. Air barriers, careful sealing of every construction joint in the building envelope, and sealing of all service penetrations through it are all used to achieve this.
Airtightness minimizes the amount of warm (or cool) air that can pass through the structure, enabling the mechanical ventilation system to recover the heat before discharging the air externally.
Ventilation
Mechanical heat recovery ventilation systems, with a heat recovery rate of over 80% and high-efficiency electronically commutated motors (ECM), are employed to maintain air quality, and to recover sufficient heat to dispense with a conventional central heating system. Since the building is essentially airtight, the rate of air change can be optimized and carefully controlled at about 0.4 air changes per hour. All ventilation ducts are insulated and sealed against leakage.
Although not compulsory, earth warming tubes (typically 200 mm (~7,9 in) diameter, 40 m (~130 ft) long at a depth of 1.5 m (~5 ft)) are often buried in the soil to act as earth-to-air heat exchangers and pre-heat (or pre-cool) the intake air for the ventilation system. In cold weather the warmed air also prevents ice formation in the heat recovery system's heat exchanger.
Alternatively, an earth to air heat exchanger, can use a liquid circuit instead of an air circuit, with a heat exchanger (battery) on the supply air.
Space heating
In addition to the heat exchanger (centre), a micro-heat pump extracts heat from the exhaust air (left) and hot water heats the ventilation air (right). The ability to control building temperature using only the normal volume of ventilation air is fundamental.
In addition to using passive solar gain, Passivhaus buildings make extensive use of their intrinsic heat from internal sources such as waste heat from lighting, white goods (major appliances) and other electrical devices (but not dedicated heaters) as well as body heat from the people and animals inside the building. (People, on average, emit heat energy equivalent to 100 Watts, see Radiation emitted by a human body).
Together with the comprehensive energy conservation measures taken, this means that a conventional central heating system is not necessary, although they are sometimes installed due to client skepticism.
Instead, Passive houses sometimes have a dual purpose 800 to 1,500 Watt heating and/or cooling element integrated with the supply air duct of the ventilation system, for use during the coldest days. It is fundamental to the design that all the heat required can be transported by the normal low air volume required for ventilation. A maximum air temperature of 50 C (122 F) is applied, to prevent any possible smell of scorching from dust that escapes the filters in the system.
The air-heating element can be heated by a small heat pump, by direct solar thermal energy, annualized geothermal solar, or simply by a natural gas or oil burner. In some cases a micro-heat pump is used to extract additional heat from the exhaust ventilation air, using it to heat either the incoming air or the hot water storage tank. Small wood-burning stoves can also be used to heat the water tank, although care is required to ensure that the room in which stove is located does not overheat.
Beyond the recovery of heat by the heat recovery ventilation unit, a well designed Passive house in the European climate should not need any supplemental heat source if the heating load is kept under 10W/m .
Because the heating capacity and the heating energy required by a passive house both are very low, the particular energy source selected has fewer financial implications than in a traditional building, although renewable energy sources are well suited to such low loads.
Lighting and electrical appliances
To minimize the total primary energy consumption, low-energy lighting (such as compact fluorescent lamps or solid-state lighting), and high-efficiency electrical appliances are normally used.
Traits of Passive Houses
Due to their design, passive houses usually have the following traits:
The air is fresh, and very clean. Note that for the parameters tested, and provided the filters (minimum F6) are maintained, HEPA quality air is provided. 0.3 air changes per hour (ACH) are recommended, otherwise the air can become "stale" (excess CO2, flushing of indoor air pollutants) and any greater, excessively dry (less than 40% humidity). This implies careful selection of interior finishes and furnishings, to minimize indoor air pollution from VOC's (e.g., formaldehyde). The use of a mechanical venting system also implies higher positive ion values.[citation needed] This can be counteracted somewhat by opening a window for a very brief time, by plants, and by indoor fountains. However, it should be noted that failure to exchange air with the outside during occupied periods is not advisable.
Because of the high resistance to heat flow (high R-value insulation), there are no "outside walls" which are colder than other walls.
Since there are no radiators, there is more space on the rooms' walls.
Inside temperature is homogeneous; it is impossible to have single rooms (e.g. the sleeping rooms) at a different temperature from the rest of the house. Note that the relatively high temperature of the sleeping areas is physiologically not considered desirable by some building scientists. Bedroom windows can be cracked slightly to alleviate this when necessary.
The temperature changes only very slowly - with ventilation and heating systems switched off, a passive house typically loses less than 0.5 C (1 F) per day (in winter), stabilizing at around 15 C (59 F) in the central European climate.
Opening windows or doors for a short time has only a very limited effect; after the windows are closed, the air very quickly returns to the "normal" temperature.
The air inside Passive Houses, due to the lack of ventilating cold air, is much drier than in 'Standard' Houses.
International comparisons
In the United States, a house built to the Passive House standard results in a building that requires space heating energy of 1 BTU per square foot per heating degree day, compared with about 5 to 15 BTUs per square foot per heating degree day for a similar building built to meet the 2003 Model Energy Efficiency Code. This is between 75 and 95% less energy for space heating and cooling than current new buildings that meet today's US energy efficiency codes. The Passivhaus in the German-language camp of Waldsee, Minnesota uses 85% less energy than a house built to Minnesota building codes.
In the United Kingdom, an average new house built to the Passive House standard would use 77% less energy for space heating, compared to the Building Regulations.
In Ireland, it is calculated that a typical house built to the Passive House standard instead of the 2002 Building Regulations would consume 85% less energy for space heating and cut space-heating related carbon emissions by 94%.
Comparison with zero energy buildings
Main article: Zero-energy building
A net zero-energy building (ZEB) is a building that over a year does not use more energy than it creates. A ZEB requires the use of onsite renewable energy technologies like photovoltaic to offset the building's primary energy use.
Criticism
While passive houses work in a temperate climate, they have not (so far) produced ideal internal conditions in a tropical climate with high levels of humidity.
See also
Energy portal
Sustainable development portal
CEPHEUS
PlusEnergy buildings
Energy-plus buildings
Rolf Disch Solar Architecture
Green building
Low-energy buildings
List of low-energy building techniques
Renewable heat
Self-sufficient homes
Thermal conductivity for an explanation of how thermal conductivity, thermal conductance, and thermal resistance are related
References
^ Definition of Passive House
^ Minergie-Standard
^ Yan Ji and Stellios Plainiotis (2006): Design for Sustainability. Beijing: China Architecture and Building Press. ISBN 7-112-08390-7
^ a b c "Houses With No Furnace but Plenty of Heat". New York Times. December 26, 2008. http://www.nytimes.com/2008/12/27/world/europe/27house.html?ref=world&pagewanted=all. Retrieved 2008-12-27. "There are now an estimated 15,000 passive houses around the world, the vast majority built in the past few years in German-speaking countries or Scandinavia."
^ "Timber Frame takes the Passivhaus tour". January 23, 2009. http://www.buildingtalk.com/news/tim/tim140.html. Retrieved 2009-06-05.
^ Institute for Housing and the Environment
^ Evaluation of the First Passive House
^ 11th International Passive House Conference 2007
^ European Continental Passive Houses
^ First US Passive House
^ Certified US Passive House
^ Construct Ireland Articles - Passive Resistance
^ Scandinavian Homes Ltd
^ Diss Express, UK - How to build a house in days
^ Passive House Requirements
^ Concepts and market acceptance of a cold climate Passive House
^ europeanpassivehouses(PEP)
^ Cost Efficient Apartment Passive House
^ "Passivhuser im Bau bis zu 14% teurer". Franz Alt. http://www.sonnenseite.com/Aktuelle+News,Passivhaeuser+im+Bau+bis+zu+14v.h.+teurer,6,a11845.html. Retrieved 2009-06-05.
^ Passive Houses in High Latitudes
^ Passive Houses in Norway
^ Annualized Geo-Solar Heating, Don Stephens Accessed 2009-02-05
^ Passivhaus Planning Package
^ Passive House Estate in Hannover-Kronsberg p72
^ Waldsee BioHaus design
^ Energy Saving Potential of Passive Houses in the UK
^ Passive Houses in Ireland
External links
Wikimedia Commons has media related to: Passive house
Passive House Institute U.S.
Passivhaus Institut
History of the Passivhaus
CEPHEUS Final Report (5MB) Major European Union research project. Technical report on as-built thermal performance.
Passive houses in Sweden: Experiences from design and construction phase Lund University (5MB)
Passive House for the Olympic Winter Games 2010il:
Categories: Alternative energy | Solar design | Energy conservation | Energy economics | Energy in Germany | Environmental design | Home | Heating, ventilating, and air conditioning | Low-energy building | Sustainable technologies | Sustainability | House typesHidden categories: All articles with unsourced statements | Articles with unsourced statements from December 2008
Prato
China Product
History
Ancient age
Archaeological findings have proved that Prato's surrounding hills were inhabited since Paleolithic times. The plain was later colonized by the Etruscans. In 1998 remains of a previously unknown city from that civilization was discovered in the neighbourhood, near Campi Bisenzio: it was of medium size and it was already a centre for wool and textile industry. According to some scholars, it could be the mythical Camars. The Etruscan city was inhabited until the 5th century BC, when, for undisclosed reasons, it decayed; control of the area was later shifted to the Romans, who had their Via Cassia pass from here, but did not build any settlement. kawasaki bayou 220
Middle Ages hello kitty coloring pages
In the early Middle Ages the Byzantine and Lombard dominations followed. The history of Prato itself begins from the 10th century, when two distinct villages, Borgo al Cornio and Castrum Prati (Prato's Castle), are known. In the following century the two settlements were united under the lords of the castle, the Alberti family, who received the imperial title of Counts of Prato. In the same period the plain was dried and a hydraulic system regulating and exploiting the waters of the Bisenzio River was created to feed the gualchierae (pre-industrial textile machines). electric motor handbook
After a siege in 1107 by the troops of Matilde of Canossa, the Alberti retreated to their family fortresses in the Bisenzio Valley: Prato could therefore develop as a free commune. Within two centuries it reached the number of 15,000 inhabitants, spurred in by the flourishing textile industry and by the presence of the Holy Belt relic. Two new lines of walls had to be built in the mid-12th century and, respectively, from the early 14th century. In 1326, in order to counter the expansionism of Florence, Prato submitted voluntarily under the seigniory of Robert of Anjou, King of Naples. However, on February 23, 1351 Joanna I of Naples sold the city to Florence in exchange of 17,500 golden florins. Prato's history therefore followed that of the former in the following centuries.
Modern age
In 1512, during the War of the League of Cambrai, the city was sacked by Spanish troops assembled by Pope Julius II and emperor Charles V to recover the nearby city of Florence for the Medici family. The severity of the sack of Prato led to the surrender of the Florentine Republic, and to the restoration of the Medici rule. The army slaughtered some 50,000 Pratesi in the streets.
In 1653 Prato obtained the status of city and became seat of a Catholic diocese. The city was embellished in particular during the 18th century.
After the unification of Italy in the 19th century, Prato became a primary industrial centre, especially in the textile sector (Italian historian Emanuele Repetti described it as the "Italian Manchester"), and population grew up to 50,000 in 1901 and to 180,000 in 2001. The town experienced a significant internal immigration; Previously part of the province of Florence, in 1992 Prato became the capital of the eponymous province.
Chinese immigration
The city of Prato has the second largest Chinese immigrant population in Italy. Legal Chinese residents in Prato on 31 December 2008 were 9,927. Local authorities estimate the number of Chinese citizens living in Prato to be around 45.000, illegal immigrants included. Most overseas Chinese come from the city of Wenzhou in the region of Zhejiang. Some of them have moved from Chinatown in Paris. The first Chinese people came to Prato in the early 1990s. The majority of Chinese work in the garment industry and ready-to-wear. Chinatown is located in the west part of the city, spreading to Porta Pistoiese in the historical centre. The local Chamber of Commerce registered over 3100 Chinese businesses by September 2008. Most of them are located in an industrial park named Macrolotto di Iolo.
Main sights
This section requires expansion.
Prato is home to many museums and other cultural monuments, including the Filippo Lippi frescoes in the Cathedral of Santo Stefano, recently restored. The Cathedral has an external pulpit by Donatello.
Palazzo Pretorio was built from the 13th century in red bricks. The part in white stone is from late-Gothic era. In the 16th century an external staircase and a watch were added. Also notable is the Palazzo Datini, built from 1383 for the merchant Francesco Datini. It has decorations by Florentine artists like Agnolo Gaddi and Niccol Gerini. In 1409 it housed Pope Alexander V and Louis of Anjou. The Palazzo degli Alberti (12th century) is home to an art gallery with works by Filippo Lippi (Prato Madonna), Giovanni Bellini (Crucifix with Jew Cemetery) and Caravaggio (The Crowning with Thorns).
The Castello dell'Imperatore is the northernmost castle built by Frederick II of Hohenstaufen in Italy. A further major attraction of the city is the Centro per l'arte contemporanea Luigi Pecci a museum and education centre concerned with contemporary arts.
Other churches include:
Santa Maria delle Carceri, commissioned by Lorenzo de' Medici to Giuliano da Sangallo in 1484. It is one Greek cross plan, inspired to Brunelleschi's Pazzi Chapel. Works lasted for some twenty years. The interior is run by a bichromatic maiolica frieze by Luca della Robbia, also author of four tondos depicting the four Evangelists in the cupola. The external faade is unfinished, only the western part being completed in the 19th century according to Sangallo's design.
Sant'Agostino, built from 1440 over an existing edifice from 1271.
San Domenico (begun in 1281), with a portal from 1310.
San Francesco (12811331). It houses a notable funerary monument of Gemriniano Inghirami (died 1460), and the frescoes by Niccol Gerini in the Migliorati Chapel.
San Fabiano, already existing in 1082. It houses precious traces of a pavement mosaic dating from the 9th-11th centuries. Also notable is the 15th century bell tower.
the late-Baroque Monastery of San Vincenzo.
Education
Higher education institutions include Il Polo Universitario "Citt di Prato" (a branch of the Universit degli Studi di Firenze) and the Monash University Centre which is located in the Palazzo Vai.
Frazioni
Prato frazioni are:
Borgonuovo, Cafaggio, Campostino, Canneto, Capezzana, Carteano, Casale, Castelnuovo, Cavagliano, Cerreto, Chiesanuova, Coiano, Figline di Prato, Filettole, Fontanelle, Galcetello, Galceti, Galciana, Gli Abatoni, Gonfienti, Grignano, I Ciliani, Il Calice, Il Cantiere, I Lecci, Il Ferro, Il Guado, Il Palco, Il Pino, Il Soccorso, Iolo, La Castellina, La Dogaia, La Macine, La Piet, La Querce, Le Badie, Le Caserane, Le Colombaie, Le Fonti, Le Fornaci, Le Lastre, Le Pantanelle, Le Sacca, Maliseti, Mazzone, Mezzana, Narnali, Paperino, Pizzidimonte, Ponte alle Vanne, Ponzano, Popolino, Purgatorio, Reggiana, Sacra Famiglia, San Giorgio a Colonica, San Giusto, San Martino, San Paolo, Santa Cristina a Pimonte, Santa Gonda, Santa Lucia, Santa Maria a Colonica, Sant'Andrea, Sant'Ippolito, Tavola, Tobbiana, Vergaio, Viaccia, Villa Fiorita
Notable citizens
Nicolo Albertini, 13th century Catholic cardinal
Antonio Brunelli, composer, theorist and maestro di capella of the Cathedral from 1607 to 1612
Francesco Datini, 14th century merchant
Ignazio Fresu, sculptor
Filippino Lippi, 16th century painter
Lorenzo Bartolini, sculptor
Curzio Malaparte, writer
Fiorenzo Magni, cyclist
Roberto Benigni, actor and director (actually born near Arezzo but he used to live in Prato with the family.)
Jury Chechi, gymnast, olympic gold medalist
Domenico Zipoli, composer
Paolo Rossi, soccer player
Christian Vieri, soccer player
Alessandro Diamanti, soccer player
International relations
See also: List of twin towns and sister cities in Italy
Twin towns Sister cities
Prato is twinned with:
Nam Dinh in Vietnam (since 1975)
Albemarle County, Virginia in USA (since 1977)
Roubaix in France (since from 1981)
Changzhou in China (since 1987)
Ebensee in Austria (since 1987)
Wangen im Allgu in Germany (since 1988)
Sarajevo in Bosnia and Herzegovina (since 1995)
Bir Lehlu in Sahrawi Arab Democratic Republic (since 1999)
Pabianice in Poland (since 2001)
Tomaszw Mazowiecki in Poland (since 1999)
Harare in Zimbabwe
See also
The Crowning with Thorns (Prato)
References
^ http://www.comune.prato.it/prato/htm/strwrld.htm
^ http://www.intoscana.it/intoscana/informarsi/inbreve.jsp?id_categoria=1210&id_sottocategoria=1211&id=245255&language=it
^ http://www.po.camcom.it/servizi/datistud/stsint.htm
^ Il Polo Universitario "Citt di Prato"
^ Monash University Prato Centre
^ "Fraternity cities on Sarajevo Official Web Site". City of Sarajevo 2001-2008. http://www.sarajevo.ba/en/stream.php?kat=147. Retrieved 2008-11-09.
External links
Wikimedia Commons has media related to: Prato
Culture in Prato
Information about Prato, Free Time Guide on Prato (Italian)
Complete Image galleries of the town, the medieval historic centre, churches and the chinese quarter (Italian)
v d e
Tuscany Comuni of the Province of Prato
Cantagallo Carmignano Montemurlo Poggio a Caiano Prato Vaiano Vernio
Categories: Cities and towns in Tuscany | Communes of the Province of Prato | PratoHidden categories: Articles containing Italian language text | Articles to be expanded from June 2008 | All articles to be expanded
Depth of field
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Acceptable sharpness
A 35 mm lens set to f/11. The depth-of-field scale (top) indicates that a subject which is anywhere between 1 and 2 meters in front of the camera will be rendered acceptably sharp. If the aperture were set to f/22 instead, everything from 0.7 meters to infinity would appear to be in focus.
Precise focus is possible at only one distance; at that distance, a point object will produce a point image. At any other distance, a point object is defocused, and will produce a blur spot shaped like the aperture, which for the purpose of analysis is usually assumed to be circular. When this circular spot is sufficiently small, it is indistinguishable from a point, and appears to be in focus; it is rendered as cceptably sharp. The diameter of the circle increases with distance from the point of focus; the largest circle that is indistinguishable from a point is known as the acceptable circle of confusion, or informally, simply as the circle of confusion. The acceptable circle of confusion is influenced by visual acuity, viewing conditions, and the amount by which the image is enlarged (Ray 2000, 5253). The increase of the circle diameter with defocus is gradual, so the limits of depth of field are not hard boundaries between sharp and unsharp. magellan gps 800
Several other factors, such as subject matter, movement, and the distance of the subject from the camera, also influence when a given defocus becomes noticeable. 123 lithium battery
The area within the depth of field appears sharp, whilst the areas in front of and beyond the depth of field appear blurry. dewalt 18v batteries
For a 35 mm motion picture, the image area on the negative is roughly 22 mm by 16 mm (0.87 in by 0.63 in). The limit of tolerable error is usually set at 0.05 mm (0.002 in) diameter. For 16 mm film, where the image area is smaller, the tolerance is stricter, 0.025 mm (0.001 in). Standard depth-of-field tables are constructed on this basis, although generally 35 mm productions set it at 0.025 mm (0.001 in). Note that the acceptable circle of confusion values for these formats are different because of the relative amount of magnification each format will need in order to be projected on a full-sized movie screen.
(A table for 35 mm still photography would be somewhat different since more of the film is used for each image and the amount of enlargement is usually much less.)
The image format size also will affect the depth of field. The larger the format size, the longer a lens will need to be to capture the same framing as a smaller format. In motion pictures, for example, a frame with a 12 degree horizontal field of view will require a 50 mm lens on 16 mm film, a 100 mm lens on 35 mm film, and a 250 mm lens on 65 mm film. Conversely, using the same focal length lens with each of these formats will yield a progressively wider image as the film format gets larger: a 50 mm lens has a horizontal field of view of 12 degrees on 16 mm film, 23.6 degrees on 35 mm film, and 55.6 degrees on 65 mm film. What this all means is that because the larger formats require longer lenses than the smaller ones, they will accordingly have a smaller depth of field. Therefore, compensations in exposure, framing, or subject distance need to be made in order to make one format look like it was filmed in another format.
f/22
f/8
f/4
f/2.8
At f/32, the background competes for the viewer attention.
At f/5.6, the flowers are isolated from the background.
At f/2.8, the cat is isolated from the background.
Effect of lens aperture
For a given subject framing and camera position, the DOF is controlled by the lens aperture diameter, which is usually specified as the f-number, the ratio of lens focal length to aperture diameter. Reducing the aperture diameter (increasing the f-number) increases the DOF; however, it also reduces the amount of light transmitted, and increases diffraction, placing a practical limit on the extent to which DOF can be increased by reducing the aperture diameter.
Motion pictures make only limited use of this control; to produce a consistent image quality from shot to shot, cinematographers usually choose a single aperture setting for interiors and another for exteriors, and adjust exposure through the use of camera filters or light levels. Aperture settings are adjusted more frequently in still photography, where variations in depth of field are used to produce a variety of special effects.
Obtaining maximum DOF
Lens DOF scales
Many lenses for small- and medium-format cameras include scales that indicate the DOF for a given focus distance and f-number; the 35 mm lens in the image above is typical. That lens includes distance scales in feet and meters; when a marked distance is set opposite the large white index mark, the focus is set to that distance. The DOF scale below the distance scales includes markings on either side of the index that correspond to f-numbers; when the lens is set to a given f-number, the DOF extends between the distances that align with the f-number markings.
Zone focusing
When the 35 mm lens above is set to f/11 and focused at approximately 1.4 m, the DOF (a one of acceptable sharpness) extends from 1 m to 2 m. Conversely, the required focus and f-number can be determined from the desired DOF limits by locating the near and far DOF limits on the lens distance scale and setting focus so that the index mark is centered between the near and far distances; the required f-number is determined by finding the markings on the DOF scale that are closest to the near and far distances (Ray 1994, 315). For the 35 mm lens above, if it were desired for the DOF to extend from 1 m to 2 m, focus would be set to approximately 1.4 m and the aperture set to f/11. The DOF limits can be determined from a scene by focusing on the farthest object to be within the DOF and noting the distance on the lens distance scale, and repeating the process for the nearest object to be within the DOF. If the near and far distances fall outside the largest f-number markings on the DOF scale, the desired DOF cannot be obtained; for example, with the 35 mm lens above, it is not possible to have the DOF extend from 0.7 m to infinity.
Some distance scales have markings for only a few distances; for example, the 35 mm lens above shows only 3 ft and 5 ft on its upper scale. Using other distances for DOF limits requires visual interpolation between marked distances; because the distance scale is nonlinear, accurate interpolation can be difficult. In most cases, English and metric distance markings are not coincident, so using both scales to note focused distances can sometimes lessen the need for interpolation. Many autofocus lenses have smaller distance and DOF scales and fewer markings than do comparable manual-focus lenses, so that determining focus and f-number from the scales on an autofocus lens may be more difficult than with a comparable manual-focus lens. In most cases, determining these settings using the lens DOF scales on an autofocus lens requires that the lens or camera body be set to manual focus.
On a view camera, the focus and f-number can be obtained by measuring the focus spread and performing simple calculations; the procedure is described in more detail in the section Focus and f-number from DOF limits. Some view cameras include DOF calculators that indicate focus and f-number without the need for any calculations by the photographer (Tillmanns 1997, 6768; Ray 2002, 23031).
Hyperfocal distance
The hyperfocal distance is the nearest focus distance at which the DOF extends to infinity; focusing the camera at the hyperfocal distance results in the largest possible depth of field for a given f-number (Ray 2000, 55). Focusing beyond the hyperfocal distance does not increase the far DOF (which already extends to infinity), but it does decrease the DOF in front of the subject, decreasing the total DOF. Some photographers consider this wasting DOF; however, see The object field method below for a rationale for doing so. If the lens includes a DOF scale, the hyperfocal distance can be set by aligning the infinity mark on the distance scale with the mark on the DOF scale corresponding to the f-number to which the lens is set. For example, with the 35 mm lens shown above set to f/11, aligning the infinity mark with the 11 to the left of the index mark on the DOF scale would set the focus to the hyperfocal distance. Focusing on the hyperfocal distance is a special case of zone focusing in which the far limit of DOF is at infinity.
The object field method
Traditional depth-of-field formulas and tables assume equal circles of confusion for near and far objects. Some authors, such as Merklinger (1992), have suggested that distant objects often need to be much sharper to be clearly recognizable, whereas closer objects, being larger on the film, do not need to be so sharp. The loss of detail in distant objects may be particularly noticeable with extreme enlargements. Achieving this additional sharpness in distant objects usually requires focusing beyond the hyperfocal distance, sometimes almost at infinity. For example, if photographing a cityscape with a traffic bollard in the foreground, this approach, termed the object field method by Merklinger, would recommend focusing very close to infinity, and stopping down to make the bollard sharp enough. With this approach, foreground objects cannot always be made perfectly sharp, but the loss of sharpness in near objects may be acceptable if recognizability of distant objects is paramount.
Other authors (Adams 1980, 51) have taken the opposite position, maintaining that slight unsharpness in foreground objects is usually more disturbing than than slight unsharpness in distant parts of a scene.
Moritz von Rohr also used an object field method, but unlike Merklinger, he used the conventional criterion of a maximum circle of confusion diameter in the image plane, leading to unequal front and rear depths of field.
Limited DOF: selective focus
Depth of field can be anywhere from a fraction of a millimeter to virtually infinite. In some cases, such as landscapes, it may be desirable to have the entire image sharp, and a large DOF is appropriate. In other cases, artistic considerations may dictate that only a part of the image be in focus, emphasizing the subject while de-emphasizing the background, perhaps giving only a suggestion of the environment (Langford 1973, 81). For example, a common technique in melodramas and horror films is a closeup of a person's face, with someone just behind that person visible but out of focus. A portrait or close-up still photograph might use a small DOF to isolate the subject from a distracting background. The use of limited DOF to emphasize one part of an image is known as selective focus, differential focus or shallow focus.
Although a small DOF implies that other parts of the image will be unsharp, it does not, by itself, determine how unsharp those parts will be. The amount of background (or foreground) blur depends on the distance from the plane of focus, so if a background is close to the subject, it may be difficult to blur sufficiently even with a small DOF. In practice, the lens f-number is usually adjusted until the background or foreground is acceptably blurred, often without direct concern for the DOF.
Sometimes, however, it is desirable to have the entire subject sharp while ensuring that the background is sufficiently unsharp. When the distance between subject and background is fixed, as is the case with many scenes, the DOF and the amount of background blur are not independent. Although it is not always possible to achieve both the desired subject sharpness and the desired background unsharpness, several techniques can be used to increase the separation of subject and background.
For a given scene and subject magnification, the background blur increases with lens focal length. If it is not important that background objects be unrecognizable, background de-emphasis can be increased by using a lens of longer focal length and increasing the subject distance to maintain the same magnification. This technique requires that sufficient space in front of the subject be available; moreover, the perspective of the scene changes because of the different camera position, and this may or may not be acceptable.
Selective focus using tilt with a Lensbaby
The situation is not as simple if it is important that a background object, such as a sign, be unrecognizable. The magnification of background objects also increases with focal length, so with the technique just described, there is little change in the recognizability of background objects. However, a lens of longer focal length may still be of some help; because of the narrower angle of view, a slight change of camera position may suffice to eliminate the distracting object from the field of view.
Although tilt and swing are normally used to maximize the part of the image that is within the DOF, they also can be used, in combination with a small f-number, to give selective focus to a plane that isn't perpendicular to the lens axis. With this technique, it is possible to have objects at greatly different distances from the camera in sharp focus and yet have a very shallow DOF. The effect can be interesting because it differs from what most viewers are accustomed to seeing.
Near:far distribution
The DOF beyond the subject is always greater than the DOF in front of the subject. When the subject is at the hyperfocal distance or beyond, the far DOF is infinite; as the subject distance decreases, near:far DOF ratio increases, approaching unity at high magnification. The oft-cited ule that 1/3 of the DOF is in front of the subject and 2/3 is beyond is true only when the subject distance is 1/3 the hyperfocal distance.
DOF vs. format size
To a first approximation, DOF is inversely proportional to format size (Stroebel 1976, 139). More precisely, if photographs with the same final-image size are taken in two different camera formats at the same subject distance with the same field of view and f-number, the DOF is, to a first approximation, inversely proportional to the format size. Though commonly used when comparing formats, the approximation is valid only when the subject distance is large in comparison with the focal length of the larger format and small in comparison with the hyperfocal distance of the smaller format.
To maintain the same field of view, the lens focal lengths must be in proportion to the format sizes. Assuming, for purposes of comparison, that the 45 format is four times the size of 35 mm format, if a 45 camera used a 300 mm lens, a 35 mm camera would need a 75 mm lens for the same field of view. For the same f-number, the image made with the 35 mm camera would have four times the DOF of the image made with the 45 camera.
If a picture is taken from the same distance using the same lens and f-number, the image from the smaller format requires greater enlargement for the same size final image, and has less DOF.
Cropping an image and enlarging to the same size final image as an uncropped image taken under the same conditions is equivalent to using a smaller format; the cropped image has less DOF (Stroebel 1976, 134, 13637).
In many cases, the DOF is fixed by the requirements of the desired image. For a given DOF and field of view, the required f-number is proportional to the format size. For example, if a 35 mm camera required f/11, a 45 camera would require f/45 to give the same DOF. For the same ISO speed, the exposure time on the 45 would be sixteen times as long; if the 35 camera required 1/250 second, the 45 camera would require 1/15 second. The longer exposure time with the larger camera might result in motion blur, especially with windy conditions, a moving subject, or an unsteady camera.
Adjusting the f-number to the camera format is equivalent to maintaining the same absolute aperture diameter; when set to the same absolute aperture diameters, both formats have the same DOF.
Derivations of these relationships are given under Derivation of the DOF formulas in the subsection DOF vs. format size.
The greater DOF with the smaller format can be either an advantage or a disadvantage, depending on the desired effect. For the same amount of foreground and background blur, a small-format camera requires a smaller f-number and allows a shorter exposure time than a large-format camera; however, many point-and-shoot digital cameras cannot provide a very shallow DOF. For example, a point-and-shoot digital camera with a 1/1.8 sensor (7.18 mm 5.32 mm) at a normal focal length and f/2.8 has the same DOF as a 35 mm camera with a normal lens at f/13.
Camera movements and DOF
When the lens axis is perpendicular to the image plane, as is normally the case, the plane of focus (POF) is parallel to the image plane, and the DOF extends between parallel planes on either side of the POF. When the lens axis is not perpendicular to the image plane, the POF is no longer parallel to the image plane; the ability to rotate the POF is known as the Scheimpflug principle. Rotation of the POF is accomplished with camera movements (tilt, a rotation of the lens about a horizontal axis, or swing, a rotation about a vertical axis). Tilt and swing are available on most view cameras, and are also available with specific lenses on some small- and medium-format cameras.
When the POF is rotated, the near and far limits of DOF are no longer parallel; the DOF becomes wedge-shaped, with the apex of the wedge nearest the camera (Merklinger 1993, 3132; Tillmanns 1997, 71). With tilt, the height of the DOF increases with distance from the camera; with swing, the width of the DOF increases with distance.
In some cases, rotating the POF can better fit the DOF to the scene, and achieve the required sharpness at a smaller f-number. Alternatively, rotating the POF, in combination with a small f-number, can minimize the part of an image that is within the DOF.
DOF formulas
The basis of these formulas is given in the section Derivation of the DOF formulas; refer to the diagram in that section for illustration of the quantities discussed below.
Hyperfocal Distance
Let f be the lens focal length, N be the lens f-number, and c be the circle of confusion for a given image format. The hyperfocal distance H is given by
Moderate-to-large distances
Let s be the distance at which the camera is focused (the ubject distance). When s is large in comparison with the lens focal length, the distance DN from the camera to the near limit of DOF and the distance DF from the camera to the far limit of DOF are
and
When the subject distance is the hyperfocal distance,
and
The depth of field DF DN is
For , the far limit of DOF is at infinity and the DOF is infinite; of course, only objects at or beyond the near limit of DOF will be recorded with acceptable sharpness.
Substituting for H and rearranging, DOF can be expressed as
Thus, for a given image format, depth of field is determined by three factors: the focal length of the lens, the f-number of the lens opening (the aperture), and the camera-to-subject distance.
Close-up
The integrated circuit package, which is in focus in this macro shot, is 2.5 mm higher than the circuit board it is mounted on. In macro photography even small distances can blur an object out of focus. At f/32 every object is within the DOF, whereas the closer one gets to f/5, the fewer the objects that are sharp. The images were taken with a 105 mm f/2.8 macro lens. At f/5 the small dust particles at the bottom right corner set examples for the circle of confusion phenomenon.
When the subject distance s approaches the focal length, using the formulas given above can result in significant errors. For close-up work, the hyperfocal distance has little applicability, and it usually is more convenient to express DOF in terms of image magnification. Let m be the magnification; when the subject distance is small in comparison with the hyperfocal distance,
so that for a given magnification, DOF is independent of focal length. Stated otherwise, for the same subject magnification, all focal lengths give approximately the same DOF. This statement is true only when the subject distance is small in comparison with the hyperfocal distance, however.
The discussion thus far has assumed a symmetrical lens for which the entrance and exit pupils coincide with the front and rear nodal planes, and for which the pupil magnification (the ratio of exit pupil diameter to that of the entrance pupil) is unity. Although this assumption usually is reasonable for large-format lenses, it often is invalid for medium- and small-format lenses.
When , the DOF for an asymmetrical lens is
where P is the pupil magnification. When the pupil magnification is unity, this equation reduces to that for a symmetrical lens.
Except for close-up and macro photography, the effect of lens asymmetry is minimal. At unity magnification, however, the errors from neglecting the pupil magnification can be significant. Consider a telephoto lens with P = 0.5 and a retrofocus wide-angle lens with P = 2, at m = 1.0. The asymmetrical-lens formula gives DOF = 6Nc and DOF = 3Nc, respectively. The symmetrical-lens formula gives DOF = 4Nc in either case. The errors are 33% and 33%, respectively.
Focus and f-number from DOF limits
For given near and far DOF limits DN and DF, the required f-number is smallest when focus is set to
When the subject distance is large in comparison with the lens focal length, the required f-number is
When the far limit of DOF is at infinity,
s = 2DN
and
In practice, these settings usually are determined on the image side of the lens, using measurements on the bed or rail with a view camera, or using lens DOF scales on manual-focus lenses for small- and medium-format cameras. If vN and vF are the image distances that correspond to the near and far limits of DOF, the required f-number is minimized when the image distance v is
In practical terms, focus is set to halfway between the near and far image distances. The required f-number is
The image distances are measured from the camera's image plane to the lens's image nodal plane, which is not always easy to locate. In most cases, focus and f-number can be determined with sufficient accuracy using the approximate formulas above, which require only the difference between the near and far image distances; view camera users sometimes refer to the difference as the focus spread (Hansma 1996, 55). Most lens DOF scales are based on the same concept.
The focus spread is related to the depth of focus. Ray (2000, 56) gives two definitions of the latter. The first is the tolerance of the position of the image plane for which an object remains acceptably sharp; the second is that the limits of depth of focus are the image-side conjugates of the near and far limits of DOF. With the first definition, focus spread and depth of focus are usually close in value though conceptually different. With the second definition, focus spread and depth of focus are the same.
Foreground and background blur
If a subject is at distance s and the foreground or background is at distance D, let the distance between the subject and the foreground or background be indicated by
The blur disk diameter b of a detail at distance xd from the subject can be expressed as a function of the focal length f, subject magnification ms, and f-number N according to
The minus sign applies to a foreground object, and the plus sign applies to a background object.
The blur increases with the distance from the subject; when , the detail is within the depth of field, and the blur is imperceptible. If the detail is only slightly outside the DOF, the blur may be only barely perceptible.
For a given subject magnification, f-number, and distance from the subject of the foreground or background detail, the degree of detail blur varies with the lens focal length. For a background detail, the blur increases with focal length; for a foreground detail, the blur decreases with focal length. For a given scene, the positions of the subject, foreground, and background usually are fixed, and the distance between subject and the foreground or background remains constant regardless of the camera position; however, to maintain constant magnification, the subject distance must vary if the focal length is changed. For small distance between the foreground or background detail, the effect of focal length is small; for large distance, the effect can be significant. For a reasonably distant background detail, the blur disk diameter is
depending only on focal length.
The blur diameter of foreground details is very large if the details are close to the lens.
The magnification of the detail also varies with focal length; for a given detail, the ratio of the blur disk diameter to imaged size of the detail is independent of focal length, depending only on the detail size and its distance from the subject. This ratio can be useful when it is important that the background be recognizable (as usually is the case in evidence or surveillance photography), or unrecognizable (as might be the case for a pictorial photographer using selective focus to isolate the subject from a distracting background). As a general rule, an object is recognizable if the blur disk diameter is one-tenth to one-fifth the size of the object or smaller (Williams 1990, 205), and unrecognizable when the blur disk diameter is the object size or greater.
The effect of focal length on background blur is illustrated in van Walree's article on Depth of field.
Practical complications
The distance scales on most medium- and small-format lenses indicate distance from the camera image plane. Most DOF formulas, including those in this article, use the object distance s from the lens front nodal plane, which often is not easy to locate. Moreover, for many zoom lenses and internal-focusing non-zoom lenses, the location of the front nodal plane, as well as focal length, changes with subject distance. When the subject distance is large in comparison with the lens focal length, the exact location of the front nodal plane is not critical; the distance is essentially the same whether measured from the front of the lens, the image plane, or the actual nodal plane. The same is not true for close-up photography; at unity magnification, a slight error in the location of the front nodal plane can result in a DOF error greater than the errors from any approximations in the DOF equations.
The asymmetrical lens formulas require knowledge of the pupil magnification, which usually is not specified for medium- and small-format lenses. The pupil magnification can be estimated by looking into the front and rear of the lens and measuring the diameters of the apparent apertures, and computing the ratio of rear diameter to front diameter (Shipman 1977, 144). However, for many zoom lenses and internal-focusing non-zoom lenses, the pupil magnification changes with subject distance, and several measurements may be required.
Limitations
Most DOF formulas, including those discussed in this article, employ several simplifications:
Paraxial (Gaussian) optics is assumed, and technically, the formulas are valid only for rays that are infinitesimally close to the lens axis. However, Gaussian optics usually is more than adequate for determining DOF, and non-paraxial formulas are sufficiently complex that requiring their use would make determination of DOF impractical in most cases.
Lens aberrations are ignored. Including the effects of aberrations is nearly impossible, because doing so requires knowledge of the specific lens design. Moreover, in well-designed lenses, most aberrations are well corrected, and at least near the optical axis, often are almost negligible when the lens is stopped down 23 steps from maximum aperture. Because lenses usually are stopped down at least to this point when DOF is of interest, ignoring aberrations usually is reasonable. Not all aberrations are reduced by stopping down, however, so actual sharpness may be slightly less than predicted by DOF formulas.
Diffraction is ignored. DOF formulas imply that any arbitrary DOF can be achieved by using a sufficiently large f-number. Because of diffraction, however, this isn't really true, as is discussed further in the section DOF and diffraction.
Post-capture manipulation of the image is ignored. Sharpening via techniques such as deconvolution or unsharp mask can increase the DOF in the final image, particularly when the original image has a large DOF. Conversely, image noise reduction can reduce the DOF.
For digital capture with color filter array sensors, demosaicing is ignored. Demosaicing alone would normally reduce the DOF, but the demosaicing algorithm used might also include sharpening.
The lens designer cannot restrict analysis to Gaussian optics and cannot ignore lens aberrations. However, the requirements of practical photography are less demanding than those of lens design, and despite the simplifications employed in development of most DOF formulas, these formulas have proven useful in determining camera settings that result in acceptably sharp pictures. It should be recognized that DOF limits are not hard boundaries between sharp and unsharp, and that there is little point in determining DOF limits to a precision of many significant figures.
DOF and diffraction
If the camera position and image framing (i.e., angle of view) have been chosen, the only means of controlling DOF is the lens aperture. Most DOF formulas imply that any arbitrary DOF can be achieved by using a sufficiently large f-number. Because of diffraction, however, this isn't really true. Once a lens is stopped down to where most aberrations are well corrected, stopping down further will decrease sharpness in the plane of focus. At the DOF limits, however, further stopping down decreases the size of the defocus blur spot, and the overall sharpness may still increase. Eventually, the defocus blur spot becomes negligibly small, and further stopping down serves only to decrease sharpness even at DOF limits (Gibson 1975, 64).
There is thus a tradeoff between sharpness in the POF and sharpness at the DOF limits. But the sharpness in the POF is always greater than that at the DOF limits; if the blur at the DOF limits is imperceptible, the blur in the POF is imperceptible as well.
For general photography, diffraction at DOF limits typically becomes significant only at fairly large f-numbers; because large f-numbers typically require long exposure times, motion blur may cause greater loss of sharpness than the loss from diffraction. The size of the diffraction blur spot depends on the effective f-number , however, so diffraction is a greater issue in close-up photography, and the tradeoff between DOF and overall sharpness can become quite noticeable (Gibson 1975, 53; Lefkowitz 1979, 84).
Optimal f-number
As a lens is stopped down, the defocus blur at the DOF limits decreases but diffraction blur increases. The presence of these two opposing factors implies a point at which the combined blur spot is minimized (Gibson 1975, 64); at that point, the f-number is optimal for image sharpness. If the final image is viewed under normal conditions (e.g., an 810 image viewed at 10), it may suffice to determine the f-number using criteria for minimum required sharpness, and there may be no practical benefit from further reducing the size of the blur spot. But this may not be true if the final image is viewed under more demanding conditions, e.g., a very large final image viewed at normal distance, or a portion of an image enlarged to normal size (Hansma 1996). Hansma also suggests that the final-image size may not be known when a photograph is taken, and obtaining the maximum practicable sharpness allows the decision to make a large final image to be made at a later time.
Determining combined defocus and diffraction
Hansma (1996) and Peterson (1996) have discussed determining the combined effects of defocus and diffraction using a root-square combination of the individual blur spots. Hansma's approach determines the f-number that will give the maximum possible sharpness; Peterson's approach determines the minimum f-number that will give the desired sharpness in the final image, and yields a maximum focus spread for which the desired sharpness can be achieved. In combination, the two methods can be regarded as giving a maximum and minimum f-number for a given situation, with the photographer free to choose any value within the range, as conditions (e.g., potential motion blur) permit. Gibson (1975, 64) gives a similar discussion, additionally considering blurring effects of camera lens aberrations, enlarging lens diffraction and aberrations, the negative emulsion, and the printing paper.
Hopkins (1955), Stokseth (1969), and Williams and Becklund (1989) have discussed the combined effects using the modulation transfer function. Conrad's Depth of Field in Depth (PDF), and Jacobson's Photographic Lenses Tutorial discuss the use of Hopkins's method specifically in regard to DOF.
Photolithography
In semiconductor photolithography applications, depth of field is extremely important as integrated circuit layout features must be printed with high accuracy at extremely small size. The difficulty is that the wafer surface is not perfectly flat, but may vary by several micrometres. Even this small variation causes some distortion in the projected image, and results in unwanted variations in the resulting pattern. Thus photolithography engineers take extreme measures to maximize the optical depth of field of the photolithography equipment. To minimize this distortion further, semiconductor manufacturers may use chemical mechanical polishing to make the wafer surface even flatter before lithographic patterning.
Ophthalmology and optometry
A person may sometimes experience better vision in daylight than at night because of an increased depth of field due to constriction of the pupil (i.e., miosis).
Digital techniques for extending DOF
At f/11, the DOF in this image of a Wolf spider is very limited.
Combining 8 images, each taken at f/11, gives extended DOF.
Focus stacking
Main article: Focus stacking
Focus stacking is a digital image processing technique which combines multiple images taken at different focus distances to give a resulting image with a greater depth of field than any of the individual source images. Available programs for multi-shot DOF enhancement include Syncroscopy AutoMontage, PhotoAcute Studio, Helicon Focus and CombineZM.
Getting sufficient depth of field can be particularly challenging in macro photography. The images to the right illustrate the extended DOF that can be achieved by combining multiple images.
Wavefront coding
Main article: Wavefront coding
Wavefront coding is a method that convolves rays in such a way that it provides an image where fields are in focus simultaneously with all planes out of focus by a constant amount.
Plenoptic cameras
Main article: Plenoptic camera
A plenoptic camera uses a microlens array to capture 4D light field information about a scene.
Derivation of the DOF formulas
DOF for symmetrical lens.
DOF limits
A symmetrical lens is illustrated at right. The subject, at distance s, is in focus at image distance v. Point objects at distances DF and DN would be in focus at image distances vF and vN, respectively; at image distance v, they are imaged as blur spots. The depth of field is controlled by the aperture stop diameter d; when the blur spot diameter is equal to the acceptable circle of confusion c, the near and far limits of DOF are at DN and DF. From similar triangles,
and
It usually is more convenient to work with the lens f-number than the aperture diameter; the f-number N is related to the lens focal length f and the aperture diameter d by
substituting into the previous equations and rearranging gives
and
The image distance v is related to an object distance s by the thin lens equation
applying this to vN and vF gives
and
solving for v, vN, and vF in these three equations, substituting into the two previous equations, and rearranging gives the near and far limits of DOF:
and
Hyperfocal distance
Setting the far limit of DOF DF to infinity and solving for the focus distance s gives
where H is the hyperfocal distance. Setting the subject distance to the hyperfocal distance and solving for the near limit of DOF gives
For any practical value of H, the focal length is negligible in comparison, so that
Substituting the approximate expression for hyperfocal distance into the formulas for the near and far limits of DOF gives
and
Combining, the depth of field DF DN is
Moderate-to-large distances
When the subject distance is large in comparison with the lens focal length,
and
so that
For , the far limit of DOF is at infinity and the DOF is infinite; of course, only objects at or beyond the near limit of DOF will be recorded with acceptable sharpness.
Close-up
When the subject distance s approaches the lens focal length, the focal length no longer is negligible, and the approximate formulas above cannot be used without introducing significant error. At close distances, the hyperfocal distance has little applicability, and it usually is more convenient to express DOF in terms of magnification. Substituting
and
into the formula for DOF and rearranging gives
after Larmore (1965, 163). At the hyperfocal distance, the terms in the denominator are equal, and the DOF is infinite. As the subject distance decreases, so does the second term in the denominator; when , the second term becomes small in comparison with the first, and
so that for a given magnification, DOF is independent of focal length. Stated otherwise, for the same subject magnification, all focal lengths for a given image format give approximately the same DOF. This statement is true only when the subject distance is small in comparison with the hyperfocal distance, however. Multiplying the numerator and denominator of the exact formula by
gives
Decreasing the focal length f increases the second term in the denominator, decreasing the denominator and increasing the value of the right-hand side, so that a shorter focal length gives greater DOF. The effect of focal length is greatest near the hyperfocal distance, and decreases as subject distance is decreased. However, the near/far perspective will differ for different focal lengths, so the difference in DOF may not be readily apparent. When the subject distance is small in comparison with the hyperfocal distance, the effect of focal length is negligible, and, as noted above, the DOF essentially is independent of focal length.
Near:far DOF ratio
From the xact equations for near and far limits of DOF, the DOF in front of the subject is
and the DOF beyond the subject is
The near:far DOF ratio is
This ratio is always less than unity; at moderate-to-large subject distances, , and
When the subject is at the hyperfocal distance or beyond, the far DOF is infinite, and the near:far ratio is zero. It commonly stated that approximately 1/3 of the DOF is in front of the subject and approximately 2/3 is beyond; however, this is true only when .
At closer subject distances, it often more convenient to express the DOF ratio in terms of the magnification
substitution into the xact equation for DOF ratio gives
As magnification increases, the near:far ratio approaches a limiting value of unity.
DOF vs. format size
When the subject distance is much less than hyperfocal, the total DOF is given to good approximation by
When additionally the magnification is small compared to unity, the value of m in the numerator can be neglected, and the formula further simplifies to
The DOF ratio of two different formats depends on what is assumed. One approach is to assume that essentially the same picture is taken with each format and enlarged to produce the same size final image, so the subject distance remains the same, the focal length is adjusted to maintain the same angle of view, and to a first approximation, magnification is in direct proportion to some characteristic dimension of each format. If both pictures are enlarged to give the same size final images with the same sharpness criteria, the circle of confusion is also in direct proportion to the format size. Thus if l is the characteristic dimension of the format,
With the same f-number, the DOF ratio is then
so the DOF ratio is in inverse proportion to the format size. This ratio is approximate, and breaks down in the macro range of the larger format (the value of m in the numerator is no longer negligible) or as distance approaches the hyperfocal distance for the smaller format (the DOF of the smaller format approaches infinity).
If the formats have approximately the same aspect ratios, the characteristic dimensions can be the format diagonals; if the aspect ratios differ considerably (e.g., 45 vs. 617), the dimensions must be chosen more carefully, and the DOF comparison may not even be meaningful.
If the same lens focal length is used in both formats, magnifications can be maintained in the ratio of the format sizes by adjusting subject distances; the DOF ratio is the same as that given above, but the images differ because of the different perspectives and angles of view.
If the same DOF is required for each format, an analysis similar to that above shows that the required f-number is in direct proportion to the format size.
Another approach is to use the same focal length with both formats at the same subject distance, so the magnification is the same, and with the same f-number,
so the DOF ratio is in direct proportion to the format size. The perspective is the same for both formats, but because of the different angles of view, the pictures are not the same.
Cropping an image and enlarging to the same size final image as an uncropped image taken under the same conditions is equivalent to using a smaller format; the cropped image requires greater enlargement and consequently has a smaller circle of confusion. The cropped image has less DOF than the uncropped image.
The aperture diameter is normally given in terms of the f-number because all lenses set to the same f-number give approximately the same image illuminance (Ray 2002, 130), simplifying exposure settings. In deriving the basic DOF equations, the substitution of f / N for the absolute aperture diameter d can be omitted, giving the DOF in terms of the absolute aperture diameter:
after Larmore (1965, 163). When the subject distance S is small in comparison with the hyperfocal distance, the second term in the denominator can be neglected, leading to
With the same subject distance and angle of view for both formats, S2 = S1, and
so the DOFs are in inverse proportion to the absolute aperture diameters. When the diameters are the same, the two formats have the same DOF. Von Rohr (1906) made this same observation, saying t this point it will be sufficient to note that all these formulae involve quantities relating exclusively to the entrance-pupil and its position with respect to the object-point, whereas the focal length of the transforming system does not enter into them. Lyon Depth of Field Outside the Box describes an approach very similar to that of von Rohr.
Focus and f-number from DOF limits
The equations for the DOF limits can be combined to eliminate Nc and solve for the subject distance. For given near and far DOF limits DN and DF, the subject distance is
the harmonic mean of the near and far distances. The equations for DOF limits also can be combined to eliminate s and solve for the required f-number, giving
When the subject distance is large in comparison with the lens focal length, this simplifies to
When the far limit of DOF is at infinity, the equations for s and N give indeterminate results. But if all terms in the numerator and denominator on the right-hand side of the equation for s are divided by DF, it is seen that when DF is at infinity,
Similarly, if all terms in the numerator and denominator on the right-hand side of the equation for N are divided by DF, it is seen that when DF is at infinity,
Most discussions of DOF concentrate on the object side of the lens, but the formulas are simpler and the measurements usually easier to make on the image side. If the basic image-side equations
and
are combined and solved for the image distance v, the result is
the harmonic mean of the near and far image distances. The basic image-side equations can also be combined and solved for N, giving
The image distances are measured from the camera's image plane to the lens's image nodal plane, which is not always easy to locate. The harmonic mean is always less than the arithmentic mean, but when the difference between the near and far image distances is reasonably small, the two means are close to equal, and focus can be set with sufficient accuracy using
This formula requires only the difference between the near and far image distances. View camera users often refer to this difference as the focus spread; it usually is measured on the bed or focusing rail. Focus is simply set to halfway between the near and far image distances.
Substituting into the equation for N and rearranging gives
One variant of the thin-lens equation is , where m is the magnification; substituting this into the equation for N gives
At moderate-to-large subject distances, m is small compared to unity, and the f-number can often be determined with sufficient accuracy using
For close-up photography, the magnification cannot be ignored, and the f-number should be determined using the first approximate formula.
As with the approximate formula for v, the approximate formulas for N require only the focus spread rather than the absolute image distances.
When the far limit of DOF is at infinity, .
On manual-focus small- and medium-format lenses, the focus and f-number usually are determined using the lens DOF scales, which often are based on the approximate equations above.
Defocus blur for background object at B.
Foreground and background blur
If the equation for the far limit of DOF is solved for c, and the far distance replaced by an arbitrary distance D, the blur disk diameter b at that distance is
When the background is at the far limit of DOF, the blur disk diameter is equal to the circle of confusion c, and the blur is just imperceptible. The diameter of the background blur disk increases with the distance to the background. A similar relationship holds for the foreground; the general expression for a defocused object at distance D is
For a given scene, the distance between the subject and a foreground or background object is usually fixed; let that distance be represented by
then
or, in terms of subject distance,
with the minus sign used for foreground objects and the plus sign used for background objects. For a relatively distant background object,
In terms of subject magnification, the subject distance is
so that, for a given f-number and subject magnification,
Differentiating b with respect to f gives
With the plus sign, the derivative is everywhere positive, so that for a background object, the blur disk size increases with focal length. With the minus sign, the derivative is everywhere negative, so that for a foreground object, the blur disk size decreases with focal length.
The magnification of the defocused object also varies with focal length; the magnification of the defocused object is
where vs is the image distance of the subject. For a defocused object with some characteristic dimension y, the imaged size of that object is
The ratio of the blur disk size to the imaged size of that object then is
so for a given defocused object, the ratio of the blur disk diameter to object size is independent of focal length, and depends only on the object size and its distance from the subject.
Asymmetrical lenses
The discussion thus far has assumed a symmetrical lens for which the entrance and exit pupils coincide with the object and image nodal planes, and for which the pupil magnification is unity. Although this assumption usually is reasonable for large-format lenses, it often is invalid for medium- and small-format lenses.
For an asymmetrical lens, the DOF ahead of the subject distance and the DOF beyond the subject distance are given by
and
where P is the pupil magnification.
Combining gives the total DOF:
When , the second term in the denominator becomes small in comparison with the first, and
When the pupil magnification is unity, the equations for asymmetrical lenses reduce to those given earlier for symmetrical lenses.
Effect of lens asymmetry
Except for close-up and macro photography, the effect of lens asymmetry is minimal. A slight rearrangement of the last equation gives
As magnification decreases, the 1 / P term becomes smaller in comparison with the 1 / m term, and eventually the effect of pupil magnification becomes negligible.
Notes
^ Strictly, because of lens aberrations and diffraction, a point object in precise focus is imaged not as a point but rather as a small spot, often called the least circle of confusion. For most treatments of DOF, including this article, the assumption of a point is sufficient.
^ Higher-end models in the Canon EOS line of cameras included a feature called depth-of-field AE (DEP) that set focus and f-number from user-determined near and far points in much the same manner as using DOF scales on manual-focus lenses (Canon Inc. 2000, 6162). The feature has not been included on models introduced after April 2004.
^ Englander describes a similar approach in his paper Apparent Depth of Field: Practical Use in Landscape Photography. (PDF); Conrad discusses this approach, under Different Circles of Confusion for Near and Far Limits of Depth of Field, and The Object Field Method, in Depth of Field in Depth (PDF)
^ Using the object field method, Merklinger (1992, 3235) describes a situation in which a portrait subject is to be sharp but a distracting sign in the background is to be unrecognizable. He concludes that with the subject and background distances fixed, no f-number will achieve both objectives, and that using a lens of different focal length will make no difference in the result.
^ Derivations of DOF formulas are given in many texts, including Larmore (1965, 161166), Ray (2000, 5356), and Ray (2002, 217220). Complete derivations also are given in Conrad's Depth of Field in Depth (PDF) and van Walree's Derivation of the DOF equations.
^ A well-illustrated discussion of pupils and pupil magnification that assumes minimal knowledge of optics and mathematics is given in Shipman (1977, 144147).
^ Williams gives the criteria for object recognition in terms of the system resolution. When resolution is limited by defocus blur, as in the context of DOF, the resolution is the blur disk diameter; when resolution is limited by diffraction, the resolution is the radius of the Airy disk, according to the Rayleigh criterion.
^ Peterson does not give a closed-form expression for the minimum f-number, though such an expression obtains from simple algebraic manipulation of his Equation 3.
^ The analytical section at the end of Gibson (1975) was originally published as agnification and Depth of Detail in Photomacrography in the Journal of the Photographic Society of America, Vol. 26, No. 6, June 1960.
^ This is discussed in Jacobson's Photographic Lenses Tutorial. and complete derivations are given in Conrad's Depth of Field in Depth (PDF) and van Walree's Derivation of the DOF quations.
See also
Photography portal
Angle of view
Bokeh
Circle of confusion
Deep focus
Depth-of-field adapter
Depth of focus
Frazier lens (very deep DOF)
Hyperfocal distance
Perspective distortion
Shallow focus
Tilted plane focus (camera movements used to achieve selective focus)
Miniature faking
References
Adams, Ansel. 1980. The Camera. The New Ansel Adams Photography Series/Book 1. Boston: New York Graphic Society. ISBN 0-8212-1092-0
Canon Inc. 2000. Canon EOS-1v/EOS-1v HS Instructions. Tokyo: Canon Inc.
Gibson, H. Lou. 1975. Close-Up Photography and Photomacrography. 2nd combined ed. Kodak Publication No. N-16. Rochester, NY: Eastman Kodak Company, Vol II: Photomacrography. ISBN 0-87985-160-0
Hansma, Paul K. 1996. View Camera Focusing in Practice. Photo Techniques, March/April 1996, 5457. Available as GIF images on the Large Format page.
Hopkins, H.H. 1955. The frequency response of a defocused optical system. Proceedings of the Royal Society A, 231:91103.
Langford, Michael J. 1973. Basic Photography. 3rd ed. Garden City, NY: Amphoto. ISBN 0-8174-0640-9
Larmore, Lewis. 1965. Introduction to Photographic Principles. 2nd ed. New York: Dover Publications, Inc.
Lefkowitz, Lester. 1979 The Manual of Close-Up Photography. Garden City, NY: Amphoto. ISBN 0-8174-2456-3
Merklinger, Harold M. 1992. The INs and OUTs of FOCUS: An Alternative Way to Estimate Depth-of-Field and Sharpness in the Photographic Image. v. 1.0.3. Bedford, Nova Scotia: Seaboard Printing Limited. ISBN 0-9695025-0-8. Version 1.03e available in PDF at http://www.trenholm.org/hmmerk/.
. 1993. Focusing the View Camera: A Scientific Way to Focus the View Camera and Estimate Depth of Field. v. 1.0. Bedford, Nova Scotia: Seaboard Printing Limited. ISBN 0-9695025-2-4. Version 1.6.1 available in PDF at http://www.trenholm.org/hmmerk/.
Peterson, Stephen. 1996. Image Sharpness and Focusing the View Camera. Photo Techniques, March/April 1996, 5153. Available as GIF images on the Large Format page.
Ray, Sidney F. 1994. Photographic Lenses and Optics. Oxford: Focal Press. ISBN 0-240-51387-8
. 2000. The geometry of image formation. In The Manual of Photography: Photographic and Digital Imaging, 9th ed. Ed. Ralph E. Jacobson, Sidney F. Ray, Geoffrey G. Atteridge, and Norman R. Axford. Oxford: Focal Press. ISBN 0-240-51574-9
. 2002. Applied Photographic Optics. 3rd ed. Oxford: Focal Press. ISBN 0-240-51540-4
Shipman, Carl. 1977. SLR Photographers Handbook. Tucson: H.P. Books. ISBN 0-912656-59-X
Stokseth, Per A. 1969. Properties of a Defocused Optical System. Journal of the Optical Society of America 59:10, Oct. 1969, 13141321.
Stroebel, Leslie. 1976. View Camera Technique. 3rd ed. London: Focal Press. ISBN 0-240-50901-3
Tillmanns, Urs. 1997. Creative Large Format: Basics and Applications. 2nd ed. Feuerthalen, Switzerland: Sinar AG. ISBN 3-7231-0030-9
von Rohr, Moritz. 1906. Die optischen Instrumente. Leipzig: B. G. Teubner
Williams, Charles S., and Becklund, Orville. 1989. Introduction to the Optical Transfer Function. New York: Wiley. Reprinted 2002, Bellingham, WA: SPIE Press, 293300. ISBN 0-8194-4336-0
Williams, John B. 1990. Image Clarity: High-Resolution Photography. Boston: Focal Press. ISBN 0-240-80033-8
Further reading
Hummel, Rob (editor). 2001. American Cinematographer Manual. 8th ed. Hollywood: ASC Press. ISBN 0-935578-15-3
External links
Wikimedia Commons has media related to: Depth of field
DOFMaster Depth of field calculator
Depth of Field explanation and comparison photographs
Depth of Fieldhe Third Dimension
Luminous Landscape demonstration that all focal lengths have approximately the same depth of field when f-number and subject image size are maintained
DOFMaster Explanation of why ll focal lengths have approximately the same depth of field only under certain conditions
Bob Atkins Digital Depth of Field
Bob Atkins DOF and Background Blur Calculator
Jeff Conrad Depth of Field in Depth (PDF). Includes derivations of most DoF formulas
Joe Englander Apparent Depth of Field: Practical Use in Landscape Photography (PDF). Alternative criteria for circle of confusion
David Jacobson Photographic Lenses Tutorial
Rik Littlefield An Introduction to Extended Depth of Field Digital Photography
Dick Lyon Depth of Field Outside the Box (PDF). A format-independent look at DOF
Justin Snodgrass Depth of Field Explained Video.
Paul van Walree Depth of field.
Paul van Walree DOF with Pupil Magnification. Includes derivation
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