My first attempt with SFX200

[Paul Manuell]

Actually, a film will only have one single ISO (formerly ASA) speed. If you are metering using a different rating, you are using a different Exposure Index ("EI").
Even the film manufactures use EI when referring to customized changes in film ratings.

And


When it comes to IR work, you will never be able to count on getting "consistently correct" in camera exposures, because your meter cannot meter IR. It only meters visible light, and we use informed guesses about how much IR light accompanies that visible light. Those guesses are, at best, imprecise - the ratio of IR to visible is quite variable.
All that being said, your results are impressive!

I shot at the box speed of 200iso, only adjusting the shutter speed so that in effect I was shooting it as if it was 12iso (4 stops slower).
Thank you very much for the explanation of how getting differences in exposures occur when shooting in infrared; the reasons are something I wouldn't have thought of so puts my mind a bit at ease about why some of the 2nd roll were a bit overexposed. And thank you too for the compliment, very much appreciated.

 

[fdonadio]

Now, the question comes to mind: is there a meter for infra-red radiation?

 

[fdonadio]

Now, the question comes to mind: is there a meter for infra-red radiation?

I googled and found some of these meters. They are kind of expensive and not designed for photography, so I guess someone would need to convert from the micro-Watt per square centimeter reading to anything meaningful to photographers.

Other option is to modify a suitable light meter, taking out its internal infrared filter (that supresses infrared light) and putting an IR72 (or your choice of filter) in its place.

 

[Sirius Glass]

Now, the question comes to mind: is there a meter for infra-red radiation?

I have gotten close enough by metering through the filter and the lens to get consistently good IR exposures and negatives. I do not know how good the exposures would have been with a CdS meter.