Fuji compared to PFG-01, 8E75, and BB-640
Posted: Tue Feb 21, 2006 1:33 am
Whats the deal with such a difference in energy? Agfa 10-20uJ/cm2 and Fuji's paper says 100-200uJ/cm2?
These old Agfa numbers were to get a density of .6 or so, for something unbleached where you could see a bit of an image, whereas in the era of holograms to be bleached the density is up there in the 2.0 -2.5 range. Having tested Agfa materials with calibrated power meters and densitometers 100 - 200 uJ/cm2 would definitely yield densities of 2.5 or so.
When I started doing d-log E curves with holo materials, I expected a change in slope of the characteristic curve as development times got longer, like in the photographic film case. But that didn't happen, even with dev. times ranging from 1' to 6'. The curves were essentially parallel, which is what the curves of photographic printing paper look like. Same shape, just shifted to the right. What was uncanny was that 4" E w/2' D gave same density as 2" E w/4' D. I should hunt up the curves in my log book to be sure, but that was quite amazing to me!
The other thing that was amazing to me, having been trained in the "Zone System" of photographic processing (expose for the shadows, develop for the highlights) was that the Agfa holographic materials' brightness and S/N ratio always peaked at density of 2.5, no matter what developer was used and what exposure time was used. So this explains how some of you get by with developing to a certain darkness.
I, myself being disciplined almost to the point of rigidity, keep my development time constant, 2' usually, and make an exposure series to tune in the best brightness. This may explain the "overmodulation" that plagues someone every so often, not necessarily a badly calculated ratio but an exposure and development that puts the density in the saturated zone at the top of the characteristic curve.