Infrared Photography Tips

All commercial infrared films are sensitive to a combination of visible and infrared light. When treated like normal film (normal speeds, no IR filter) they behave like a normal film; they show no special characteristics.
 

An example infrared photo. infrared trees

"Infrared pictures without filters always produce results similar to black and white pictures, missing [the IR] tonal value graduation. Color IR pictures show a strong blue-green tint and little color differentiation."

An example infrared photo. infrared sky and skin

Therefore, you must block out visible light in order to get prints with the characteristics associated with infrared photography like white foliage, dark sky (etc.) This is achieved with filters.

Focusing
Camera lenses are normally calculated for the visible spectrum. Focusing scales of high-quality lenses have an infrared index (a red dot next to the focus markings) to which the focus is set for infrared photography.

Exposing
IR Film Correctly (ISO ratings & other factors) Some IR films can be shot at various ISO settings and others can not. Changing the ISO can produce interesting effects. For example, According to Laurie White Hayball, rating Kodak at ISO 100 increases grain and lowers contrast, ISO 400 increases contrast and lessens grain. There is also ISO flexibility in Ilford SFX 200 film. It can be rated from ISO 50 to 200. Not all films have such flexibility. For example, Konica 750 does not underexpose well. It is best to test a film's abilities beforehand.

There is also filter factor to take into account. According to B+W, the average sensitivity of black and white infrared film is about ISO 50/18-degrees. Kodak infrared film with the B+W filter #092 is about ISO 20/14-degrees; with the B+W filter #093 it is about ISO 10/11-degrees.

Theresa Airey, infrared photo

Finally, environmental issues play a role. The above values are highly dependent on the strength of the infrared radiation present in the scene, which is much higher when the sun is low. (The impressive white foliage effect appears the strongest at low sun levels.)

Thus, precise ISO ratings are difficult to obtain. It is advisable to first test a film and filter combination.

IR Film sensitivity (IR range)
Infrared films are responsive to all visible light and some ultraviolet light. Visible light starts at about 380nm and gives way to invisible IR light at around 730nm.

Film IR sensitivity range
Visible Light 380-730
Kodak HIE Visible light + up to 925nm
Konica 750 Visible light + up to 820nm
Agfa APX Visible light + up to 775nm
Ilford SFX 200 Visible light + up to 740nm
Maco IR820C Visible light + up to 820nm

Using Filters
As mentioned earlier, if you do not block out the visible light it will overpower the IR effect leaving you with a regular-looking negative. That is why a yellow, orange, red or opaque filter is a must in IR photography. Different filters block out different amounts of visible light.

Filter Exposure increase (f-stops) IR Sensitivity
  IR film Regular B&W films Blocks all light below (apx.)
UV warming 0 0 No DATA available
#8 yellow 1 1 450nm
#15 orange* 1 1 2/3 500nm
#25 red 2 3 600nm
#29 dark red 2 4 1/3 620nm
#70 No DATA available No DATA available 680nm
#89B opaque No DATA available No DATA available 720nm
#88A opaque No DATA available No DATA available 780nm
#87 opaque 3 Don't use 730nm
#88A opaque 3 Don't use 710nm
#87C opaque 12 or more Don't use 780nm
B+W #92 near-opaque 4-6 Don't use 650nm
B+W #93 opaque Depends on film Don't use 750nm
B+W #99 amber* Depends on film No DATA available 520nm

*Orange-colored filter reduces the blue-green sensitivity for color infrared films. It helps avoid blue tint and differentiates colors more evenly. Filter factor depends on film sensitivity.

Recommended Reading:
If you really want to perfect your infrared photography, these two books by Laurie White are fantastic. Within their clearly-written pages you will find a wealth of information about shooting infrared in easy-to-understand language. She thoroughly covers everything you need to shoot infrared including films, filters, printing and more.

#1419 Infrared Photography Handbook
#1715 Advanced Infrared Photography Handbook