Newly made large format dry plates available! Look:
https://www.pictoriographica.com
Post in haste, repent at leisure...
The RR had beautiful glass, like new, and the cemented doublets were pretty thin. Most of the difference in meter readings was probably due to loss from reflections at the air/glass interfaces, and very little due to absorption.
The triplets in the Dagor were a little thicker, so the difference in readings after inserting the lens in the light path between it and the RR were probably due to absorption. Most of the absorption was probably occurring in one of the cement layers in the front group which is a bit hazy. A pristine uncoated Dagor might have given readings almost the same as the RR.
The T-R was a late uncoated one, the cemented quintuplets were very thick, and the light was passing through a lot of glass. I think most of the stop and a half loss was due to absorption.
Thanks for all the info!
My brother still has his Atwater Kent collection he put together in the 1970s.
You may not know this but the Horseman exposure computer has no aperture markings. It indicates only the appropriate shutter speed for the light that would fall on the film. Utility of the device is realized best with bellows extension, unmarked lenses, improper or missing aperture scale and sloppy aperture mechanisms.
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