B & W Infrared film

I have been experimenting shooting nature and scenics with Kodak HIE black and white infrared film. The film is not DX coded and really doesn't carry an ISO rating. I have read a book that says to set the camera ISO manually to 200 and shoot with a 25A red filter (which means that you are effectively shooting at an ISO 50 since the 25A costs you 2 stops). I would welcome any comments to this strategy.

This film does require some experimentation with exposure, and I found Kodak's film instruction sheet confusing. I exposed my first roll in a manual exposure camera (Nikon FTN), and metered at ISO 50 without the filter, then added the 25A filter and made the exposure. My negatives were grossly over exposed. I should have metered at ISO 200 without the filter, then exposed with the filter. I have another roll in the camera now and am planning to do some film speed tests this time (which I should have done first!). After seeing my ISO 50 negatives, I think maybe even ISO 400 might be a better setting with my camera/filter combination.

 

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Remember that the 25A filter doen't cost 2 stops of exposure in the IR (infra red) region, it will mostly pass IR. It is just needed to cut the visual light to which the IR film is also sensitive.

 

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Because you have no idea what your meter's sensitivity to IR is, you need to meter without the filter, then add the filter before making the exposure (put your camera in manual mode so it won't change the exposure when you put on the filter). In doing this, you make the assumption that the IR brightness of the scene is proportional to the visual brightness of the scene. This will not be true in all situations, but bracketing will get you the exposure you need. Set your meter at ISO 200, then bracket +/- 2 stops until you get experience with the needed exposure.

You should read the photo.net pages on IR photography and visit the

links given there. Also read the IR section of the original

photo.net Q&A. You will find answers to your questions there.

 

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This is an old question and has been answered (in detail) many

times before.