The effects of reciprocity law failure seem to be acknowledged for very long
exposures but not generally accepted for very short exposures. Since I know
for sure reciprocity law failure cuts both ways, I began a search that lead
me to http://webh.kodak.com/productInfo/catalog/techInfo/e31.shtml.
This most dry treatment of Reciprocity and Special Filter Data for KODAK
Films does a good job defining reciprocity law failure, long- and
short-exposure effects and product family data tables for adjusting
exposure, development or filtration as needed. It also pointed out a fact I
was unaware of - high speed reciprocity law failure has been all but
eliminated from today's *color* films except for VERICOLOR II Professional
/Type L (VPL) and VERICOLOR HC Professional (VHC); it remains a factor in
B&W emulsions.
I do find it interesting that Kodak says exposure times longer than 10
seconds with Pro 400 (PPF) is not recommended at all; no correction filter
or exposure compensation. Curious since this is my astro film of choice
because of its broad spectral sensitivity and relatively low reciprocity
failure rate. It seems to give pretty fair results after 45-90 minute
exposures. I run out of guiding skill long before the film runs out of the
ability to collect photons. I also find it interesting that with only one
exception, 1/10,000 sec is the shortest exosure time discussed. I can't
help but believe that for ultra-short exposure times,
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