Re: Velvia 50 and 100 Reciprocity Correction
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.
Re: Velvia 50 and 100 Reciprocity Correction
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'.
Re: Velvia 50 and 100 Reciprocity Correction
Kodak Ektar 100 fits a very nice curve, from the only available test for reciprocity I was able to find. This is unfiltered of course.
y = 0.759x + 0.555x^1.3
Re: Velvia 50 and 100 Reciprocity Correction
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 :)
Re: Velvia 50 and 100 Reciprocity Correction
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.
Re: Velvia 50 and 100 Reciprocity Correction
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! :)