View Full Version : Why calibrate densitometer?

16-Dec-2009, 06:56
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?

Mark Woods
16-Dec-2009, 10:19
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.

16-Dec-2009, 10:41
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.

16-Dec-2009, 11:58
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.

Lachlan 717
16-Dec-2009, 13:23
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.


16-Dec-2009, 13:24
Thanx folks.