I have been experimenting with infrared photography with the Efke IR820 Aura and Ilford SFX200 films. If you start looking into IR photography it can be a bit confusing at first. Googling the film name will probably yield lots of unexpected questions in forums and even more, seemingly, conflicting answers to these questions. While getting into infrared photography myself, I started to make sense of it slowly and wrote down my findings below; I hope that it helps you to get started too.
Photo above: Dovecot in the walled garden, Eastcote House Gardens. Efke IR820 Aura f/11, 0.5 seconds, filter: Hoya R72; Developed in APH 09 1:40 for 11 minutes. Agitation: 2 inversions every 30 seconds.
At the moment of writing, I think only two infrared films are available and several more films that have extended sensitivity to red:
Efke IR820 available in normal and AURA versions. The latter doesn’t have an anti-halation layer and can create some interesting effects when the light reflects off the back of the camera. This film is also sold under the name Maco IR820c Precision Infrared film. ** update: This film is no longer available after the Fotokemika factory in Croatia shut down **
Ilford SFX200 film which isn’t a true infrared film but does have some extended sensitivity to infrared up to 740nm.
Rollei Retro 80S is also red sensitive to 750nm which puts it in the same class as the Ilford SFX200 film.
Ilford Delta 3200
The popular Kodak HIE film has been discontinued in 2008, unfortunately.
The use of a filter is required to bring out the sensitivity of the film to red light. If you were to use an infrared sensitive film without any filter, you can expect a normal black and white photo.
Some people recommend a normal red filter, like the 25A as is used in black and white photography, but I would recommend buying one of the special infrared filters like the Hoya R72 or the IR-720 filter to maximize the effect. Both filters block all wavelengths shorter than 720nm to only let the infrared light through. The problem is that the filter will appear opaque to the eye so you will need to do all focussing before putting the filter on the lens. I usually focus, put the lens in manual focus mode if it is an auto focus lens and proceed by putting the filter in front of the lens.
Ilford does make the Ilford SFX200 filter available but I didn’t have good results with that filter in combination with the Ilford SFX200 film, the results I got with SFX200 film in combination with a Hoya R72 filter were much better.
There are other, stronger infrared filters available, but do make sure that the filter still passes through light for which the film you are using is sensitive, or else you will end up with no image.
As the result of an infrared photo is quite unpredictable and you cannot chimp on an SLR, I would certainly recommend bracketing each shot at least +1 and -1 stop.
As the filters usually recommended with infrared film are blocking out so much light, the exposure needs to be corrected. For example the filter factor for the Hoya R72 filter is 16 which translates into 4 stops.
If you are using an external light meter or would like to use the TTL lightmeter on your camera before putting on the filter, the clever thing to do is to take the filter factor into consideration when setting the EI of the film on the meter or camera. For example, the boxspeed of the Efke film is 100 ISO, to take the filter factor into consideration, you would set the EI at the meter at 6 ISO (100-50-25-12-6) and then you can set the recommended exposure time for the aperture used manually on the camera.
If your camera has TTL metering, you could use the camera settings of the exposure after you put the filter on the lens, in that case leave the ISO settings on the camera at the boxspeed of the film. This could be a bit of a gamble as it is possible that the lightmeter your camera uses is not (very) sensitive to the light that passes the filter which may result in bad exposures. You’ll need to experiment to find out.
Another option is to use the various rules of thumb you can find. I did some research and found that the recommended starting exposure for Efke IR820 is 0.5 seconds at f/11 for a bright sunny day. This is also a good way to find out how your camera TTL lightmeter works: if the camera recommends something close to this under these circumstances, it is likely that the lightmeter of your camera works fine with this filter.
If you have manual focus lenses you might have noticed the red line/dot/diamond that is located just to the left of the centre of the lens in the area that usually lists the different apertures and that you may have used to maximize the depth of field for a given aperture. As infrared light with its long wavelength focuses slightly differently from visible light, you need to adjust the focus a bit after you focused for the visible light unless your lens is marked as APO. The idea is that after focussing and optionally correcting for the depth of field, you turn the focus ring to the left such that the point of the focus ring that was in the centre of the lens now aligns with the red line/dot/diamond.
Unfortunately this is usually not possible for auto focus lenses. In that case you will need to solve the problem by selecting an aperture such that the object you want to focus on is included in the depth of field. However, be aware that infrared light will increase any lens diffraction so it is recommended to not automatically select the smallest of apertures. Keep it at f/11 or f/16, I would say, and avoid f/22 or f/32.
Be very careful when loading infrared film as it is easily fogged. Surprisingly enough, it is the 35mm versions of these films that are in danger of fogging the most. The felt in the light trap of a 35mm film cartridge is not infrared opaque and loading the film in any other place but a dark room could easily spoil the first few exposures.
Beware of unexpected light sources or leaks that can fog the film. For instance, my Pentax 645NII camera imprints exposure data on the edge of the negatives and this did fog the Efke film I was using. Plastic development tanks and plastic backs of cameras are usually safe to use, but note that the transparent window in the back of some 35mm cameras that shows the film information on the cartridge inside can be a cause of fogging and it would be probably best to cover it up with some aluminium foil and tape.
Note that infrared film is not sensitive to heat radiation, it doesn’t supply night vision or heat vision. Heat is indeed infrared radiation but with wavelengths far longer than the wavelengths in the sensitive area of the film. This is a good thing, probably, as otherwise we could only shoot infrared film from very expensive cameras with extensive cooling. The infrared films register the infrared radiation from light sources as it is reflected from the different subjects. For instance, chlorophyll in leaves absorbs the ultraviolet light and reflects most of the infrared light which results in leaves turning almost white on infrared film.
Still, you should develop exposed infrared film as quickly as possible, preferably on the same day as waiting longer than necessary will only increase the risk of increased base fog on the negatives. And, like any other film, do store infrared film in a cool place before use, preferably a freezer.