One of the most elementary and important questions people new to infrared photography ask is what the film speed is. There are very good reasons why a straightforward answer cannot be given for this. Without getting into full detail at this point, let me just say that there are industry standards for measuring a normal visible light film's sensitivity. There are also industry standards for the designing and calibrating of light meters, that when used in conjunction with the appropriate films, give accurate and repeatable results. These standards of measurement and calibration do not exist for infrared photography. Therefore, ASA settings do not apply. Because of this, we are on our own. Different brands of light meters, whether the ones in our cameras or flashes or our handheld ones all respond differently to infrared light. Metering for infrared photography is normally done one of two ways.

NOT through the filter
The most typical is to set the film speed dial on the camera to ASA 100 or so and then bracket. The filter is then placed in front of the lens and the shutter snapped. This is convenient for most people unless they are shooting moving objects.  This method can be reliable for a given set of lighting conditions only. Since the camera's meter is seeing unfiltered light, it doesn't really know how much of it is infrared. But if the proportion of infrared light to visible light is constant, the method works. For example, at noon under a clear blue sky the sun is steady and strong. By experimentation, it might be determined that the correct film speed to set the camera at is 125. As long as the lighting doesn't change, ASA 125 will be correct. However, if the sky becomes cloudy, it will still be very bright outside, but the proportion of visible to infrared light will be different. An entirely different setting may be required for morning sun and for evening sun as well as for flash or tungsten lighting because in each case, the ratio of infrared light to visible light will be different. As a further example, fluorescent lighting contains virtually no infrared light, despite appearing very bright to our eyes and to the meter.

Through the filter
This method has a number of disadvantages although it is probably more repeatable under changing lighting conditions. It can be cumbersome to put the filter on the lens, meter the scene, remove the filter, compose the shot, replace the filter and snap the photo. This is especially true if one lacks a tripod. I've taken a number of photos of my fingers holding the filter!

One variation on metering through the filter is to use a handheld meter. This is the method I prefer the most. I use a Minolta Autometer 3F with a #87 filter glued to the underside of the reflection attachment. The #87 filter transmits no visible light, so any light that the meter does see is sure to be infrared. I find this to be much more reliable than metering without the filter. So far it has not proven to be foolproof, but I am working on making it better.

Another issue is where to place the filter. If the filter is a #25 or #29, it can be placed in front of the lens and left there. The viewfinder will be a dark red, but at least the filter does not have to be removed to compose and focus the shot. With an opaque #89B, #87 or #87C filter, things get a bit more difficult. Since one cannot see through the filter to compose or focus the shot, the filter cannot be in front of the lens.  Then the filter must be put back to snap the picture. As inconvenient as this is, it is what most people choose to do.

A better location for the filter is between the cameras film rails. When using an opaque filter, this allows one to see through the lens to compose and focus the shot.

Placing the filter between the film rails (BTFR)
By placing the filter BTFR, the film sees the filter, but the photographers eye does not. This allows for normal operation of the camera. To mount a (gelatin or polyester, not glass) filter in this position, open the back of the camera and notice the two rails located over and under the shutter window. These are raised about a millimeter or so over the plane of the shutter. This is just barely enough room. You will need to cut a filter to the exact height of the space between the rails, and just about a quarter inch longer than the shutter is wide. This is approximately 24 mm x 40 mm. Carefully cut the filter so that it just barely, yet completely covers the space between the top and bottom rails. If it is too big, the filter will buckle. If it is too small, it will result in a thin overexposed stripe in that spot of all of your pictures. Carefully tape the filter in place with office tape, and iron out any high spots with your fingernail.

In my opinion, this is the best place to put the filter. For years, I used a #87 gelatin filter in front of the lens. It worked, but it was a pain in the neck. A word of caution for BTFR however. Since the filter is DIRECTLY in front of the film, it must be EXQUISITELY clean! Any minor scratch, fingerprint, speck of dust, etc., will reproduce as black in your prints. Small black spots are hard enough to spot out, but a long scratch is virtually hopeless. My advice is to cut two or three filters down to size and carry them with you. Since Kodak's HIE film must be loaded and unloaded in complete darkness, keep a changing bag handy as well. Every roll or two inspect the filter for dust and scratches. Remember to check both sides by removing the lens and setting the shutter speed to BULB and viewing the filter that way. NEVER touch the filter. Remove dust with a fine brush or canned air. If you must blow on it, at least be careful not to spit. Replace the filter if it becomes scratched. One last thing: it will serve you well to keep the inside of the camera back as well as the inside of the changing bag free of dust.

You may want to cover your pressure plate if it is textured. In the photos above, the pressure plate is smooth. If it is not, you will get markings on your negatives when using Kodak HIE film. This is because the film does not have an antihalation layer on the back of the film. Without this layer, light passes through the film, reflects off the pressure plate and fogs the film from the back. The graph below shows that the pressure plate, although black in the vsible region is increasingly reflective near the infrared region.This is what causes the popular "halo" around images on HIE film. If the pressure plate is textured, a pattern shows up. To prevent this, I'd recommend taping a piece of 120 backing paper in place over the pressure plate.

How to determine if your camera or other light meter can measure infrared light

Many people want to know how to meter for infrared light.  If you do not own a handheld meter, you may be able to use your camera's meter. To find out if your camera's meter is IR sensitive, just put a black IR filter over the lens (#89B, #87 or #87C) making sure there is no light leakage around the outside and see if you get a reading. Don't do this under fluorescent lights. Point the camera at an incandescent bulb or go outside. If you get any valid reading at, you can probably meter IR without modifying the camera. Not all cameras are created equal though.

Some years ago, I did a simple test. I set my ASA dial to 12,800 on my Canon A-1. I covered the camera's viewfinder so stray light couldn't get in through the window. Using an 87 filter over the lens, I metered and exposed through the filter at different ASA settings. Then I processed for my usual time. I use HC-110 70F 5 min. I made a few prints from the negatives and based on that, I determined that the film speed for the #87 filter is 6400. I then used to use a filter between the film rails, and metered through another filter that I removed to compose the shot. I always shoot on manual.

Recently, I've done the same thing using my Minolta Autometer 3F. With this meter, I can place a filter over the light sensor whether I'm using the meter as a reflected light, incident or flash meter. Because of the lack of standards for metering infrared light that I mentioned previously, I have to set the ASA to 3200 on this meter to get the same readings as my Canon at 6400.

Wow! An ASA of 6400, that's really fast you say. It's not. You must remember, ASA as we know and use it does not apply here. The meter in my Canon must not be very sensitive to infrared light for me to have to set the film speed dial that high. All I am doing is determining how to set the meter, in order to get correctly exposed negatives. Your meter may require a very different film speed setting, but it really doesn't matter.

A simple film speed test
When metering infrared light, and I'll assume for this discussion that you are metering through an opaque filter, forethought and consistency are key. Let me describe a simple film speed test:
1. Set the camera up on a tripod at midday under a clear blue sky. Compose a shot that includes at least the following: open shade, blue sky, rock or pavement, green grass or tree leaves. If your typical subjects are weddings, include a white dress and a black jacket, or where something comparable and stand in the picture yourself. If you usually shoot indoors, set up your test there.
2. Choose an important element in the scene. Try to choose an element that you want to have fairly dark in the final print, but still maintain full detail. If you are outside, this will probably be rock, pavement or tree bark. This would be Zone 3 for you fanatics out there. (like me)
3. Adjust the meter's film speed setting to its highest value. With the filter over the meter (or camera lens) meter this part of the picture, being careful to meter only this part of the scene. Also be careful not to cast a shadow over the part you are metering.
4. Write down the film speed setting you have set and the reading that it gave you.
5. Set your camera to manual and adjust the film speed and F# to the indicated settings and shoot.
6. Expose the next 12 shots bracketing plus and minus 3 stops in ? stop increments if possible. If not, get as close to this as you can.
7. Repeat the test but instead meter off of something that you would like as white in the final print, yet with full detail. This would be Zone 7.  Note that metering off of green grass or leaves may give different results than metering off a white dress or white paint. You may want to try both with the remainder of the roll.
8. Remember write down everything. Record for each shot the frame number, the camera's settings and equivalent film speed and what portion of the scene it was metered off.
9. Develop the film at the recommended time and temperature for your choice of developer. Most people use HC-110, D-76 or Xtol. You can deviate from this later if needed.
10. Make a contact sheet, exposing the print for the minimum exposure needed for maximum black. This will give you some headroom later if needed.
11. Carefully evaluate the contact sheet and make several enlargements of the best exposed shots and determine what the effective film speed is depending on what you've metered off of. You'll find that metering off grass definitely requires a different setting than metering off pavement or even more so, blue sky.
12. If you determine that the required film speed setting is higher than the maximum setting on the meter, try adding more layers of filter until the setting falls within range. Obviously, this is easier with a handheld meter.

Understanding why infrared pictures have more contrast and how to control it
If you've looked at most infrared photographs, you've probably noticed that they tend to be contrastier than normal photographs. Some of this is due to our perception of the photograph and what we expect to see, and some of it is real. First, we view the world with our eyes which are sensitive only to visible light, hence the term. Visible light is officially defined as the range of the electromagnetic spectrum between 380 and 720 nanometers. Below this is Ultraviolet light and above it is Infrared light. These ranges are not sharply defined, but for the sake of ease, these are fair numbers. Most infrared films are sensitive to a wide range of colors, ranging from UV to IR. They do vary in overall light sensitivity as well as spectral sensitivity.

Most people prefer Kodak's HIE black and white infrared film. It is very fast, meaning it requires short exposures, and it also is sensitive further into the IR range of wavelengths. Infrared light is not the same as heat. A common misconception is that IR films can record heat or see in total darkness. The range of wavelengths of Kodak's HIE film extends only out to approximately 950 nm, peaking at 800 nm. Heat waves have much longer wavelengths than this. Another infrared film is Macophot's 820 IR. This film is sensitive out to about 820 nm, but it's overall sensitivity is much lower than Kodak's HIE, about 6 stops. Also available is Konica's 750IR, and sensitive to about 750 nm, this can just barely be called an infrared film. All of these films are also visible light sensitive. Silver has an inherent sensitivity to UV and blue light. Sensitizing silver to longer wavelengths requires special dyes, with infrared sensitivity being the most difficult to acheive. The spectral sensitivity of Kodak HIE can be seen at  http://www.kodak.com/global/en/professional/support/techPubs/f13/f002_0333ac.gif

So what does this have to do with contrast? When we photograph a scene with regular black and white film, we can vary the contrast to some degree by using filters over the lens. If a yellow filter is used, shadows become deeper and with a red filter, deeper yet. This is because lower wavelength colors, such as blue scatter more than longer wavelength colors, such as red. This is why the sky is blue and why snow sometimes appears blue. The more we filter out the lower wavelengths, the deeper the shadows become. Now take this one step further for infrared light. Depending on which filter is used, contrast will increase or decrease because of the ratio of shorter wavelengths to longer wavelengths. This is why images made with a #25 filter appear lower in contrast to images made with a #87 filter.

The film's emulsion may also be inherently high in contrast. When processed normally in HC-110, Kodak HIE has a contrast index of about .80 which is equilvalent to approximately N + 2.5. A normal black and white film has a contrast index of about .50 when developed this way, giving approximately "N". The graph below on the left shows how gamma relates to degree of "N". The values are calculated by assuming Zone 1 has a density of .10 D and Zone 8 has a density of 1.20 D and the characteristic curve is straight, with no toe. So, this is just to make an approximation and to illustrate a point. The graph on the right is the characteristic curve of Kodak HIE. It has a midtone gamma of 1.0 but a contrast index of .90. According to the chart on the left, it is equilvalent to about N+3, which is about right.

So this goes a long way in explaining why infrared images tend to be higher in contrast than regular black and white photos. Keep in mind that they don't have to be though. All of the same rules of exposing for the shadows and developing for the highlights and etc., still apply. With reduced development, HIE could yield normal contrast and some particular subject matter may be better off with this. There is so much creative control!

David Romano 2001