Provia 100F is a very stable film, so testing is a little tricky. From all the measured data I've been able to find, the best fit for it's reciprocity characteristics is as follows:
y = 0.9727x + 7.629E-7x^3
The E means it is *10^-7 which makes it very small... 0.0000007629 to be precise. Sorry bout that! It's what happens when a film has very very little reciprocity failure.
Here is an approximation for unfiltered non-colour-corrected velvia.
y = -0.9718 + 1.088x^1.1
Sure makes Velvia 50's reciprocity failure not seem as severe as before!
It's not as neat because filter factors are hard to *extract* from exposure information. Obviously as with all of this stuff it is all somewhat fuzzy but should be 'good enough'.
Most information seems to specify that Kodak E100G doesn't suffer noticeable reciprocity failure even at 10 minutes so I won't bother plotting that one.
Portra 400 has scarce information but being a 400 speed film I probably won't do any long exposures with it.
That's all the films in my fridge atm, so unless someone else wants a particular film plotted, I've done all I need to
Thanks, great info! Do you know if the old Provia (RDP II) has the same or similar reciprocity characteristics as the newer? I have 3 old boxes I'd like to experiment with doing long exposures.
Old Provia RDP-II has worse reciprocity characteristics and colour shift than Provia 100F. Fuji recommend 1/2 stop at 32s and a full stop at 2min with RDPII... Whereas 100F has essentially no reciprocity failure until around 6 minutes and even then it's only about 1/10 stop.
With only the information of no correction up to 16s, 1/2 stop at 32s and 1 stop at 120s I can derive an equation of
y = 0.6046x ^1.25
For RDP-II. Good luck!
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