The issue with reciprocity charts is that the reciprocity failure of films differs depending on the lighting conditions the film's being used for.
Originally Posted by johnnywalker
It's often forgotten for instance that films have an ISO speed for Daylight and a different speed for Tungsten light and reciprocity failure is also affected by the type of light. So take 3 extremes a lens stopped down to f45 in sunlight perhaps with an ND filter and an exposure time of 10 seconds, a low light evening shot at f4 @ 10 seconds and a poorly lit tungsten light shot of say f11 @10 seconds.
There's important differences in the spectral components of those 3 conditions and also the contrasts, so any reciprocity ajustment will be different as will any necessary tweaking (B&W) to get the best contrast range. So this is why Ilford use a single generous reciprocity chart.
Foma's figures for reciprocity are way different to the figures I found from testing under the conditions I shoot their films.
Rather than relying on manufacturers charts it's far more importnat to do some tests (or barcket) to find the best exposure adjustment for the conditions you'll be shooting in.
Last edited by Ian Grant; 01-19-2013 at 04:15 AM. Click to view previous post history.