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Technical Background to Infrared Photography

The Effect

The 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 move toinfrared.

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. In the 1930s 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 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.

Digital

As digital imaging has replaced film for everyday and professional photography it has 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?

  • Find a specialised infrared-capable camera. Fujifilm in the USA have produced three such cameras recently, aimed at forensics professionals. There is the IS Pro which is based on the FinePix S5 Pro which is itself based on the excellent Nikon D200. The earlier FinePix S3 Pro UVIR camera is now discontinued as the S3 it was based on has been superceded. The IS Pro joins the IS-1 which, although not as versatile as the IS Pro or the S3 (which was also based on a Nikon body and took Nikon-fit lenses) looks very useful. The images I have seen from it are good, the idiosyncratic Fuji CCD sensor has 9 megapixels and the camera has image stabilisation (the IS Pro will presumably use Nikkor stabilised lenses).

    FujiFilm UK are marketing the IS-1 and IS Pro for scientific, medical and forensic use ... and professional 'fine art' as well. (The American End User Licence Agreement is somewhat draconian: it asks for your intended use, makes you promise to be good and even requires you to notify Fuji if you sell the camera.)

    Note that the IS Pro is sensitive to UV as well as IR (as was the S3 mod), although a quartz lens is needed to get good UV sensitivity. Full marks to Fuji for taking this seriously even if their pricing and marketing are aimed at a more 'industrial' market than an artistic one.
  • Use a Sony camera with 'Night Shot, which moves the infrared blocking filter away from the imaging chip and was intended for photography in the dark. Night Shot cameras have an infrared LED which turns on when the facility is enabled'. In theory this would be a perfect solution. You take an infrared filter, mount it on the camera, switch on Night Shot and, hey-presto, you have a good quality infrared camera. Unfortunately, after someone discovered the erroneously-named 'X-Ray Effect' whereby you could take photographs through a thin layer of clothing (particularly bathing suits) Sony crippled the facility by forcing the camera to take long exposures with the aperture wide open. As usual the activities of a few neredowells have ruined a perfectly good option for thousands of legitimate users of infrared photography! There is a (partial) way around this and if you put an infrared filter plus 12 (or so) stops of ND filters on the cameras and use the lowest sensitivity setting you will get pretty good results, but hand-holding is difficult and you get vignetting at the widest zoom. The good news is that you can see what you're shooting on the digital viewfinder, auto-focus will still work but, because the lens is unlikely to be corrected for infrared focus, the camera will focus on infinity thinking that it's only a few metres away. So for any close-up work you will need yet another filter.
  • Use long exposures to get through the filtering. The infrared blocking filters are not usually 100% effective so if you put an infrared filter in front of the camera lens you will probably see something. With stills cameras you will probably find you need very long exposures and this leads to noise. The test to see whether your digital camera has any useful infrared sensitivity is to point it at a TV remote control, press a button on the remote, and see if you can see the dot light up. If you shoot this way in colour then you will probably get curious pseudo-colours in the image. These are artefacts of the chip, internal colour filtering, and the way the RGB image is processed in the camera and don't have any significant real meaning. Some chips give a blueish effect and some a yellowish one. If you can't shoot RAW with your camera then I strongly recommend that you set a special 'infrared white balance' by pointing the camera with filter at a patch of grass in full sun and setting a custom white balance on this. This will minimise quantising errors on some of your colour channels by rebalancing them. (I tried this 'brute force' technique with my Sony PC7 DV camcorder, which has poor infrared blocking, and you can see the results on another page where you can see how the infrared light in a scene compares with the red, green and blue. A movie taken in Amsterdam using this technique is available. It uses the Sorensen QuickTime 2 Codec.)
  • Remove the blocking filter so you can put an infrared filter on the camera and shoot away. Some Sigma digital SLRs make this very easy because the blocking filter is part of the user-removable sensor shield inside the body of the camera. One Kodak professional camera came with a removable filter. In most other cameras this is a delicate job that would void any warranty but there are some companies (MaxMax and LifePixel in the USA and ACS in the UK) who will do this for you if you send them your camera. If you do remove the blocking filter you may run into problems: the blocking filter may also be the antialiasing filter - which removes jaggies - so you would have to do some subtle blurring of the resulting images to compensate for this; the blocking filter may help set the focusing distances so you'll have to replace it with clear glass of exactly (very exactly) the same thickness; you may damage the sensor; and unless you get a filter for the lens which has exactly the same characteristics as the blocking filter, you can't use the camera for normal photography again.

Film

Infrared 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.

Kodak

Kodak has now virtually ceased production of infrared films. Their 35mm EKTACHROME colour infrared films finished production in June 2007 due to low demand and the workhorse 35mm High Speed black and white infrared film ceased 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.

The film I used most was Kodak HIE, AKA High Speed Infrared with the type number HIE 135-36. It is a black and white negative film and came in rolls of 36 exposures in its 35mm format.

You had to guess the exposure, although as a starting point the sensitivity could be taken to be 50 ISO/ASA if you used a red (#25) filter and used an external light meter. Alternatively I increasingly metered through the lens (and filter) and setting the internal light meter to 400 ISO/ASA. I always bracketed from this one stop in either direction. The film did not have a great latitude and was very grainy, especially when the exposure was not 'right' (in other words, the exposure lies outside the linear part of the film's response curve), but often the grain enhanced the look of the image.

This infrared film was not sensitive to heat. It was 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 film pictures that you can access from the photo menu on this site were 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 could see to frame. Focusing was done by eye and then adjusted because the lenses I used are not adjusted to focus the longer wavelengths of infrared along with the visible light. You 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 exhibited what someone at Kodak described to me as a 'light pipe' effect. This meant that you had to handle the film in complete darkness until it was processed because light could travel along the base into the 35mm film canister. For this reason, preparing for shooting always included going somewhere totally dark to load the film in the camera. This effect was 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 was 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 was 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 long discontinued. Colour infrared Ektachrome slide film from Kodak was originally known as camouflage-detection film. Originally this needed to be processed using the E-4 process which was a task only handled by a few labs in the world. The film was eventually reformulated to use the E-6 process, which made processing it a lot easier, and called EIR. The only Kodak infrared filmleft in production is Aerochrome III 1443, which is effectively the same as EIR but larger. You can get a data sheet via the Kodak web site.

Colour infrared film is usually exposed through 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 remotely 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 although the movie was eventually shot conventionally.

Current suppliers: Rollei/Maco, Efke/Fotokemika, Ilford and Adox

It 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.

Harman Techology, the born-again Ilford as I used to call it (and carrying the name of Ilford's founder), produce an 'extended red' film in 35mm format, which they rather quaintly call 'miniature film'. I am told that this was the film used in speed trap cameras in the UK. It is called SFX200. This film went off the radar for a while but is now back although I couldn't find reference to it on Harman's web site other than in the Ilford products list. Spectral sensitivity goes down to about 750 nm so with appropriate filtering you can see the Wood effect.

Berlin-based Adox Fotowerke were actually the first photochemical manufacturer in the world and industrialised the dry-plate process when they were founded in 1860. However, in the 1960s Adox's plant was sold to Fotokemika. The new Adox company (originally named FOTOIMPEX) have been inporting Efke into Germany and are now planning to become a boutique manufacturer specialising in black and white film. There is an Adox 820 film which appears to use the Maco emulsion.

Konica, Agfa and older films

The first commercially available infrared films were produced by Ilford and Kodak in the early 1930s. It is unclear to me (so far) which came first but the Times newspaper printed examples shot with the Ilford stock from 1932 onwards. Early examples are available through the Times online service, which (if you are in the UK) you may also be able access through your local library service. The first printed image was of a woman, taken in the dark, and published March 21st 1932.

Prior to this, most infrared photogaphers sensitised their own plates and were often interested in astronomical applications such as spectroscopy. The eariest extant infrared landscape photographs are those from Professor Robert Williams Wood in 1910 (in the USA) and 1911 (in Italy) and those taken by Kenneth Mees (then of Wratten & Wainwright and later of Kodak Research) in Portugal in 1910.

Otmar Helwich's 1930s 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.

Konica 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 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 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 refers to SN-10 as Russian Color Infrared,2 dye layer, est. ASA 64,chlorophyl response is green.

[Updated August 2010]

More background on infrared photography
Thermal Imaging NASA IR Video Camera IR 'Colour' Mapping
Imaging Abstracts Noctovision  
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