Focusing with Infrared Film Apogee Photo Magazine Focusing When Using Infrared Film by Michael Fulks Special consideration must be given when focusing the camera using infrared film.
Some lenses have an infrared guide to help.
Other lenses may require focusing tests. A reader's question last month prompted me to think that I had treated focusing with infrared film a little too lightly, in the last article on Infrared. With that in mind I would like to discuss this subject a little more in depth. While it may seem counter intuitive, light waves of different wavelengths do not focus on the same plane when passing through a simple lens. If you could put a blue filter over an older camera and focus and then switched to a red filter, you would find that the image through the red filter was slightly out of focus.