Quote Originally Posted by Dan Fromm View Post
+1

My friend Eric Beltrando (visit his site www.dioptrique.info to see the results of his calculations) insists that Boyer Beryls (Dagor clones, and very like Dagors; Beryls, Beryl Ss, and Emeraudes all have the same prescription) cover 70 degrees and can be counted on for only 55 degrees in stringent applications, e.g., photoengraving.

People tend to see what they want to see, whether it is there or not.

Other makers' dagor clones are much the same. Between ~ 1912 and ~ 1950 Berthiot's coverage claims for their f/6.8 Perigraphe Ser. VIb shrank remarkably, from 95 degrees to 65 degrees. Same lens, different films and criteria of acceptable image quality. Coverage is a sometime thing but fantasy goes on forever.
Interesting. That's almost exactly what Schneider-Kreuznach specified as coverage for the last batch of Kern 14" Dagors, the multicoated ones.

An old copy of "Photographic Optics (Cox)" gives the coverage as 70 degrees.

I had at one time an S-K 300mm Doppel Anastigmat, which is a Dagor clone. It's every bit a Dagor, and comparing mine with a CPG Berlin 30cm Dagor of the same vintage, the Schneider was a bit sharper from f:6.8 to f:11 - after that I could see no difference.