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Re: light source issue

Phil Davis

9:15 23 Apr 05

Miles --

You're very likely to encounter some reciprocity effects with the 45a but they may not be significant. Multiple additive exposures cause the so-called "intermittency effect" to kick in to reduce the total exposure effect to some extent, and if the accumulated total is much greater then 1/2 second there'll be some further reduction. But these influences are probably not worth worrying about in this exposure range; and you can minimize their effects on your test data by keeping the exposure time constant for all tests, and adjusting the aperture to control the exposure effect as necessary for films of different ISO rating.

Consistency is much more important than absolute "accuracy" here. Standardize your test methods and control them as carefully as you can, then trust your test data unless and until you discover a consistent exposure error in the field.