older DAGOR and coated AM DAGOR

[qiutaolee]

What is the different in coverage between older no coated 12" GOERZ DAGOR and coated 12" AM GOERZ DAGOR?

[David A. Goldfarb]

The coated one should have better contrast, but the older one is still pretty good. The older one may illuminate a larger image circle, but the outer edges of the circle might not be so sharp.

In my opinion, it's still good to have coverage beyond the circle of good definition, because you don't always have important detail in the corners, and in such cases, it would be better to have some sort of image rather than vignetting. The downside of that, is reduced contrast due to bellows flare, but you can control that with a compendium shade.

That said, if you can choose between the coated and uncoated, take the coated one.

[Jim Galli]

I don't think there is a difference between the older Series III Berlin Dagor's and the American Optical Co. Dagor's as far as image circle. Where you got into a smaller than before circle was when Schneider had Kern of Switzerland make their Gold Dot series Dagor's.

[David A. Goldfarb]

Jim, you've handled more of these than I have, but my 168mm Ser. III covers 8x10" and I've heard reports that not all of them do, so there seems to be some variability there. Always best to test the lens in hand, of course.

[sanking]

"I don't think there is a difference between the older Series III Berlin Dagor's and the American Optical Co. Dagor's as far as image circle. Where you got into a smaller than before circle was when Schneider had Kern of Switzerland make their Gold Dot series Dagor's."

I disagree with Jim on this. I have examined quite a number of Dagors of both vintages and the older ones, from the 20s and 30s, have almost always had a larger circle of coverage. My belief is that late model Dagors from the 40s and 50s are either mechanically vignetted to cut down on contrast or the cell spacing is optimized to give better performance in the center than at the edges.

The 14" Kern Dagor is another matter altogether. The coverage is so much less than what was possible with even late model 14" Dagors that I strongly suspect that there was a major lens re-design for this lens.