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If I'm just determining my PEI, does my densitometer need to be calibrated? I'm just looking for a relative difference of .10 between base-plus-fog and Z1 right? If my densitometer is off both measuresments will be off by that same amount but I can stiill calculate the difference right?
Interesting. I do calibrate my densitometer with calibrated piece of film for the high end and just set it to zero when there is no film. The low end is simple.
If you don't have a calibration standard, then I'd pick a piece of well processed film with a density around 1.8 and check that periodically to make sure the densitometer does not drift with time.
I agree, it would have to be way, out of alignment to mess up the 0.1 measurement.
correct, you are looking for the difference betwen base+fog and zone1 value. Providing the base+fog value is reasonable then there should be no need to calibrate even if in reality it is out by a little bit. Only if you have unexpected base+fog might you think about a calibration check but it could be you do have high (or low) base+fog.
Simple enough to calibrate even if you don't have specific "factory" calibration stock.
Just fine a base + fog piece of film, run a density measure on it, record the outcome and then put it away in a dark and dry place for any future recalibration.
Any difference in its indicated density over time will show as a difference to this intial reading.
But, as far as I know, use of relative difference is the important thing.
Lachlan.
Thanx folks.