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Technical Background to Infrared PhotographyThe EffectThe results of using monochrome infrared film are dream-like and other-worldly. Live, healthy foliage both transmits and reflects a lot of near infrared; so much so that you can use this feature to test remotely for the health of foliage. Infrared light also cuts through atmospheric haze. This is one reason why aerial and satellite imagery includes infrared. In infrared light, foliage looks 'white'. Since an open sky has no infrared, the sky goes black and the clouds really stand out. For the same reason there is little infrared in shadows (which are lit by ambient light ... the sky and reflections ... rather than by the light source) and so the contrast in a scene will increase. You can get this effect to some extent by using a deep red filter on black and white film but the effect is greater when you add in infrared. Infrared imaging is often used to detect heat loss and to find people by their body heat. This is far infrared thermal imaging, of a longer wavelength than the near infrared light used in these photographs. Far infrared is detected electronically rather than by using film. Over 70 years ago John Logie Baird produced a working infrared video system which he called Noctovision and infrared film has been around for about the same time. In the golden age of movies, or at least back and white movies, infrared film was used to enable night shots to be done during the day. This is known as 'Day for Night' (or in French La Nuit Americaine and is of course the title of Truffaut's best movie). In colour the method is to use indoor/tungsten stock and underexpose or under-print but infrared works does the job for monochrome movies. A dark sky with bright moon-lit clouds, deep shadows and ghostly foliage are characteristics that match our 'view' of the darkness. So all you need to do is underexpose the shot a bit and, hey-presto it's night. Why not just shoot at night? Well, it's partly the technicalities but was probably more to do with high union overtime rates. DigitalAs digital imaging replaces film for everyday and professional photography it will become increasingly difficult to buy infrared film as well. Digital cameras can be used instead of film for black and white infrared imaging relatively easily but, to my knowledge, there is currently no camera either current or proposed which will fill the same niche as the colour Ektachrome/Aero film. There was a Kodak digital camera that did this but it was of relatively poor resolution (by current standards), very expensive, and only produced in limited quantities. The CCD and CMOS chips used for imaging in modern digital cameras and camcorders are inherently very sensitive to near infrared (as sensitive as they are to visible light) and this is usually filtered out to avoid contaminating the colour rendition. To shoot infrared you will need to use an opaque filter (eg Hoya R72) as a deep red filter does not block enough visible light for useful results. This means that if your electronic viewfinder does not show images all the time (as with digital SLRs) then you have to use a tripod, compose the shot without the filter, put the filter on, adjust the focus and then take the shot. The viewfinder screen will always show you what you have just taken however. It is possible to use a Hoya ND400 filter, which is very dark, and which will show some of the Wood effect while still showing something dim through the viewfinder. I haven't found this as good as a true infrared filter however. So what are the options for using digital stills cameras for infrared photography?
FilmInfrared film can be used in pretty well any manual (or manual-capable) camera. It must be kept cool - or frozen in the case of the colour infrared - and the Kodak HIE has to be loaded and unloaded in complete darkness. You can use a deep red or opaque infrared filter but with a red filter you can usually hand hold in sunlight and compose through the viewfinder of an SLR. A range-finder camera would be even easier to use. Focus will probably need to be adjusted and many lenses have an infrared mark: you focus as normal and the move the focus round by the distance between the 'normal' mark and the infrared mark. KodakKodak now seem to be stopping production of infrared films. Their 35mm EKTACHROME colour infrared films finished production in June 2007 due to low demand and now the workhorse 35mm High Speed black and white 25mm infrared film will cease in December 2007. The film will be missed not only for its IR capabilities but also for its ideosyncratic halation; not a function of infrared but a result of the way the film was made. To paraphrase John Cleese, it is an ex-film ... it has ceased to be ... it has run down the curtain to join the choir invisible ... literally in this case. But for the moment ... let's just pretend it never happened. The film I have used most is Kodak HIE and they have information about the film on their web site. This link goes to an HTML page which also offers you the ability to download a PDF and a PostScript version of the information. Kodak's film is called High Speed Infrared with the type number HIE 135-36. It is a black and white negative film and comes in rolls of 36 exposures in its 35mm format. You have to guess the exposure, although as a starting point the sensitivity can be taken to be 50 ISO/ASA if you use a red (#25) filter and meter with an external light meter. Alternatively I am increasingly metering through the lens (and filter) and setting the internal light meter to 400 ISO/ASA. I always bracket from this one stop in either direction. The film does not have a great latitude and it is very grainy, especially when the exposure is not 'right' (in other words, the exposure lies outside the linear part of the film's response curve), but often the grain enhances the look of the image. This infrared film is not really sensitive to heat. It is sensitive to some visible light but also to near infrared ... you could say that this is light that we just don't happen to see because its wavelength is a little too long. Unless they say otherwise, the monochrome pictures that you can access from the photo menu on this site are taken in a combination of red and infrared light. Adding red (by using a deep red filter ... a #25 ... instead of using a 'black' infrared one such as an #87) at least means I can see to frame. Focusing is done by eye and then the focus is adjusted because the lenses I use are not adjusted to focus the longer wavelengths of infrared along with the visible light. You have to set the lens to focus a little nearer than for visible light and most lenses will have an infrared mark next to the normal focus mark. The base of the film exhibits what someone at Kodak described to me as a 'light pipe' effect. This means that you have to handle the film in complete darkness until it is processed because light can travel along the base into the 35mm film canister. For this reason, preparing for shooting always includes going somewhere totally dark to load the film in the camera. This effect is due to the lack of an anti-halation coating, which would normally stop light 'bouncing' around inside the film. The increase in the effect with long exposures is probably due to light reflecting off the blades of the diaphragm that changes the lens aperture, which is more pronounced at longer wavelengths. So it is actually due to a small f-stop rather than long exposure ... although the two usually go together. The visible light equivalent is known as diaphragm stars which appear on highlights. For large format users it was also possible to get 4x5 and even 8x10 versions of the Kodak film but these were difficult to obtain, with large orders necessary, and have now been discontinued. Colour infrared Ektachrome slide film from Kodak was originally known as camouflage-detection film. Until a few years ago, this needed to be processed using the E-4 process which was a task only handled by a few labs in the world. A few years ago the film was reformulated to use the E-6 process, which made processing it a lot easier. The later version is called EIR and you can access the data sheet on the Kodak web site. Colour infrared film is usually used with an orange or yellow (minus-blue) filter and the result is a colour shift resulting from the way the colour dyes and the sensitive layers are coupled together. Infrared comes out red, red comes out green and green comes out blue. Blue is filtered out (as is UV, to which all layers are also sensitive). The amount of red in the final image is much greater with the E-6 colour film, so while the E-4 film worked best (for me) with an orange filter I used yellow with the E-6. People look very pale and foliage looks red or magenta. This film is also used by forestry people to judge how healthy their trees are. As the trees become ill or 'stressed' their colour infrared 'colour' shifts towards magenta. You can see how this works on the colour-mapping page. Another point of trivia is that the E-4 film base polarised light so it could not be used for polarised projection of stereoscopic pairs without being duped. The Kodak High Speed Infrared film was also available in 16mm movie format but this is classed as 'military sensitive material' and was almost impossible to export from the USA so I never got round to trying it. Kodak produced a limited amount of Super-16mm colour infrared movie film for a project called Wristcutters. Current suppliers: Rollei/Maco, Efke/Fotokemika and IlfordIt seems possible that film will become a 'boutique' item, with smaller suppliers filling the demand from specialist photographers. The two current front-runners are the German company Hans O Mahn and Co and Croatian chemists Fotokemika, who are using Mahn's emulsion formulation. Mahn now market their film under the famous Rollei banner while Fotokemika's brand is Efke. Mahn did once produce an infrared film without an anti-halation layer but this is no longer made and so all films from other manufacturers have a narrower spectral sensitivity than Kodak HIE and do not exhibit the characteristic halation. It is important to note that both brands include medium and even sheet format films. While the future of infrared film from suppliers other than Kodak is uncertain, there is also a 'white knight' relative newcomer to this field: a German company called Hans O Mahn & Co from Hamburg. They are still very bullish about infrared film and are still extending their portfolio of infrared and extended red films:
I believe that the anti-halation layer can be washed off these films. The born-again Ilford produce an 'extended red' film in 35mm and 120 formats. I am told that this was the film used in speed trap cameras in the UK. It is called SFX200 (data sheet). [This film went off the radar for a while but is now back.] Spectral sensitivity goes down to about 750 nm so with appropriate filtering you can see the Wood effect. Konica, Agfa and older filmsKonica used to produce a monochrome infrared film, which was available in roll film as well as 35mm, known as Infrared 750nm. Being large enough for 6x9 and similar negs and transparencies, this film did not 'suffer' from the grain of the Kodak film. Ah well ... there goes some of the art. The results were similar to the Kodak but, with a deep red (25) filter, the bright foliage effect is not as pronounced and there is increased contrast. The grain was, however, noticeably finer. Without a filter the Konica had an equivalent speed of 32 ISO which makes it much slower than the Kodak ... so out comes the tripod. The spectral response of the Konica was also different since it didn't go quite as far down the spectrum as the Kodak and it was reputed to be easier to judge the exposure. Whereas the Kodak has (had?) a continuous, if irregular, spectral response, the Konica had no green sensitivity at all ... the exact inverse of the eye's response curve. Results were more subtle and I have heard of it being used for portraiture. Some of the other photographers I link to from the home page have pictures taken with this film as well as the Kodak and some of my shots have used it. [Konica/Minolta, have pulled out of the camera/film business.] Agfa-Gaevert used to produce two extended red films (aimed at surveillance applications) - Agfapan APX 200 S and Agfapan APX 400 S. These went slightly into near infrared (with similar response curves to the Ilford) but not as far as the Kodak and Konica films. The Agfa films were also only available in long 35mm rolls. There were also infrared films produced by other manufacturers over the years, notably by the Russians. Literature from NASA mentions a Russian infrared film called SN-10 which was used in a joint Russian/American film test (PDF) conducted in 1996 to show the effects of radiation on photographic film flown aboard the Mir space station for 130 days. Other NASA literature mentions a Russian colour infrared film. Going back to the mid 1930s, Otmar Helwich's book 'Practical Infra-Red Photography' includes infrared photos taken by the author using a variety of Ilford plates and the book tells us that infrared sensitive film was available at the time from Ilford, Kodak, Agfa (in Berlin) and R Guilleminot, Boespflug and Company in Paris (who closed down in 1994). Ilford had recently introduced roll film infrared as well as plates and this was seen as expanding the appeal to the 'more than half of all amateurs' who used roll film. The IR sensitivity was given as between 640 and 880 nm with a peak at 810 nm. Kodak are noted as producing a cine film called K-film, used in the film industry presumably for 'day-for-night' and 'travelling matte' applications. Herbert William Greenwood's book 'Infra-red for Everyone', published a few years later, also mentions Kodak, Ilford and Agfa plates and roll films. [Updated April 2007]
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