Infrared film

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Tree example IR.jpg Tree example VIS.jpg

Above: near infrared image of a tree
Below: the same tree in the visible range of the electromagnetic spectrum

As infrared film refers to a photographic film , which for the near infrared region of the electromagnetic spectrum sensitized is, which is the range between 700 and 900  nm . Infrared films are used in infrared photography. Infrared color film, which shows the infrared spectrum invisible to humans in one or more specific colors - and thus does not reproduce these colors naturally when they come from the object - is also known as false color film .

Recording materials

Infrared image on Kodak HIE film (Botanical Garden, Bern)

As a general rule, the film speed printed on the film package is misleading. By using infrared filters (also called IR blocking filters), the film speed specified by the manufacturers is never achieved in practice. The higher the blocking effect of the filter in the infrared range, the lower the film sensitivity that can be used in practice.

Infrared films are divided into two types:

  • Real infrared films with a spectral sensitivity up to over 800 nm. The infrared effect is very pronounced with real infrared films and is achieved with filters from 665 nm. The Kodak HIE, which was no longer available, was the best-known film of this type. The typical white coloration of the leaves ( Wood effect ) was intensified in this film by overexposure because the film did not have an antihalation layer.
  • Films with "extended red sensitivity", which partially and with low sensitivity transitions into the infrared range. This is mostly material that was developed for traffic monitoring or aerial photography. The spectrum of the spectral sensitivity usually only extends to just over 700 nm and then drops off steeply. This means that the typical infrared effect can only be achieved with strong filters (from 715 nm) and correspondingly longer exposure times. In practice, this disadvantage is partially offset by the fact that these films often have a higher basic sensitivity than true infrared films.

Infrared films are offered as:

  • Black and white films that are more or less sensitive in the infrared range. The visible light is completely switched off by camera filters (infrared filters) or for the most part (yellow, orange and red filters ). A typical result is an extremely dark sky and a white coloration of the leaves ( wood effect ).
  • Color films whose color rendering shows “ wrong colors ”. This means that the colors shown do not correspond to the perception of the human eye, but rather the infrared areas are "translated" into those of visible light (so-called false color film). Such materials are used in aerial photographs, for example for mapping forest damage and in aerial archeology , and more rarely in the artistic field.

handling

Edge veil by infrared sensor

In principle, all cameras can be equipped with infrared film; only models that use an image counter based on infrared light are restricted . The exposure made by the counter can, depending on the camera, extend to the edge of the photographs. These models include the Minolta Dynax 4 or various newer cameras from other manufacturers. It is also recommended to use fixed focal lengths, as zoom lenses can lead to incorrect exposures if the light is reflected between the glass elements. It should be checked in each individual case how severe the impairments of the negative really are.

Particular care should be taken when inserting some infrared films into the camera where the carrier does not have antihalation protection (e.g. Efke IR 820 Aura or Kodak HIE). In these cases, light can fall through the film tongue onto the unexposed film. In particular, films that do not use conventional acetate but polyester as a carrier can be pre-exposed very easily because the crystal-clear polyester works particularly well as a light guide right into the cartridge. It is urgently advisable to only insert infrared films that do not have a halo protection into the camera where pre-exposure can be ruled out - i.e. in absolute darkness. On the other hand, the assumption that infrared films should always be inserted into the camera in the dark holds true to some extent to this day, but is not correct. The decisive factor for handling is not whether the material is sensitive to infrared, but whether it has antihalation protection.

The processing of film material must take place in absolute darkness.

When it comes to development, black and white infrared films hardly differ from conventional black and white films. Possibly. the infrared permeability of development boxes must be taken into account. Some color infrared films may require special development processes, e.g. B. Kodak AR-5 or AN-6 for scientifically useful results. However, the Kodak EIR and Aerochrome 1443 infrared color films can also be processed in C-41 and E-6, respectively, but the film speed has different values ​​and the color reproduction is not suitable for all scientific purposes.

Photographic effects

The following effects occur in photographic practice:

  • Since chlorophyll a and b hardly absorb any more above 700 nm (infrared range), i. H. Leaves become almost transparent to infrared rays and because the cellulose layer under the chlorophyll is highly infrared reflective, leaves and grasses are white in infrared black and white images (also known as the Wood effect ). False color films show healthy and fresh leaves and grasses in red, while camouflage green and pathological and dry, green plants are shown in blue.
  • Oxy-hemoglobin is largely transparent in the range from 650 nm to 750 nm and is displayed as light / transparent.
  • Dark or black sky, as the Rayleigh scattering decreases with the 4th power of the wavelength.
  • Lower atmospheric scattering, as Mie scattering and Rayleigh scattering decrease with wavelength. Infrared landscape recordings are therefore not much obstructed by haze.
  • Motifs in the animal world can be invisibly illuminated with IR in the range of 800 nm to 820 nm without them noticing it.

providers

True infrared films with a spectral sensitivity above 780 nm

  • up to 820 nm (ISO 400/27 °): Rollei Infrared 400 / 400S, the "S" of the newer version "400S" stands for the synthetic film base
  • up to 900 nm Kodak Aerochrome Infrared Film 2443 (Estar backing) Assemblies: 70mm x 100 ', 5 "roll film and 9.5" roll film

Films with extended red sensitivity below 780 nm

  • up to 750 nm (ISO 200/24 °): Rollei Superpan 200 (formerly Agfa Aviphot Pan 200)
  • up to 750 nm (ISO 100/21 °): Rollei Retro 80S (formerly Agfa Aviphot Pan 80)
  • up to 740 nm (ISO 200/24 ​​°): Ilford SFX 200
  • up to 730 nm (ISO 400/27 °): Rollei Retro 400S (formerly Agfa APX 400)
  • up to 720 nm (ISO 400/27 °): Kodak Hawkeye surveillance film 2485

Films no longer produced

  • up to 900 nm (ASA 50 daylight, ASA 125 artificial light with WRATTEN filter 25 or similar) Kodak High Speed ​​Infrared 2481 HIE in packs: 135-36 / 135x150 '
  • up to 900 nm Kodak Professional High-Speed ​​Infrared Film HIE 135-36, discontinued 2007
  • up to 900 nm Kodak Ektachrome Infrared Film 2236 Packing: IE 135-36
  • up to 900 nm Kodak High Speed ​​Infrared Film, 2481
  • up to 900 nm Kodak High Speed ​​Infrared Film, 4143 (similar to 2481) sheet film (Estar Thick backing)
  • up to 900 nm Kodak Infrared Aerographic Film 2424 (Estar backing)
  • up to 900 nm Kodak EKTACHROME Professional Infrared EIR Film (false color film)
  • up to 900 nm (EAFS 40): Kodak Aerochrome III infrared film 1443 (false color film)
  • up to 820 nm (ISO 100/21 °): Efke IR 820
  • up to 820 nm (ISO 100/21 °): Efke IR 820 Aura (identical to Efke IR 820, but with overexposure to increase the infrared effect)
  • up to 820 nm (ISO 100/21 °): Maco IR 820c (identical to Efke IR 820)
  • up to 750 nm (ISO 100/21 °): Maco IR 750c
  • up to 750 nm (ISO 32/16 °): Konica Infrared 750 (until 2005)

Note: The film speed is only a rough guide. They depend significantly on the IR filter used and on the development process.

literature

  • Rudolf Hillebrand: Infrared photography on a different wavelength . 112 pages. Publishing house photography ( review )
  • Hugh Milsom: Infra-Red Photography: A Complete Workshop Guide . 176 pages. Fountain Press ( Homepage )

See also

Individual evidence

  1. ^ Development of an infrared film at photohomepage.de, accessed on March 31, 2013
  2. ↑ a b c Digitaltruth Photo: Description of the infrared-sensitive Rollei films , accessed on May 30, 2013
  3. ↑ Maco website: Rollei Infrared 400S 135-36 ( Memento from May 9, 2013)
  4. ↑ https://www.macodirect.de/film/infrarotfilm/ Macodirect Infrared Films
  5. ↑ a b c d e f Kodak Reference Guide R-50 1982/83
  6. ↑ https://www.macodirect.de/film/schwarzweissfilm/rollei-superpan-200-135-36 Rollei Superpan 200 135-36
  7. ↑ Data sheet of the Ilford SfX 200 , PDF, 48 kB
  8. ↑ Data sheet of the Kodak Hawkeye surveillance film 2485 , (PDF, 85 kB)
  9. ↑ http://wwwuk.kodak.com/global/en/professional/support/techPubs/f13/f13.pdf Datasheet KODAK PROFESSIONAL High-Speed ​​Infrared Film
  10. ↑ Data sheet of the Kodak Ektachrome Professional Infrared ( Memento from April 20, 2016)
  11. ↑ http://www.tpub.com/photographyadv/51.htm EAFS is not the same as ISO (English)
  12. ↑ Data sheet of the Kodak Aerochrome III , AS-77, (2005), PDF, accessed on February 3, 2019
  13. ↑ Fotoimpex: Product description of the Efke IR 820 , accessed on May 30, 2013
  14. ↑ http://www.maco-photo.de/files/images/MACO_IR820c_DT.pdf

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