25" B&L process lens

[Dan Dozer]

For you lens guys out there - I have a 25" F10 B&L Process Anastigmat which VM lists as a "4 glass Gauss design". They also list a Process Apochromatic that says it is a Dialyt type design.

In simple terms, were these two different types of lens designs for their process lenses and how might they be different in performance? Or are the process anastigmat and process apochromatic actually the same lens? I haven't really shot with it much before (very heavy lens with big bellows draw on the 8 x 20" = stability problems). Seems to have quite a large image circle.

[Jim Fitzgerald]

Dan, it seems to me like you need to build a bigger camera for it!! Something like a 14x17 or larger!!

[Dan Dozer]

You're right Jim - this lens would work on your 14 x 17 and probably even on Hugo's 16 x 20. Maybe next time we get together, we should strap it to your big beast and try it out.

[Dan Fromm]

Dan, why don't you ask your lens what it is? If a dialyte, the elements are () )( | )( (), if a 4/4 double Gauss (( (( | )) )). | represents the diaphragm.

As a practical matter, most process lenses perform similarly. Usually fairly narrow angle -- the big exceptions are some Dagor types, e.g., early G-Clarons, and some plasmat types, e.g., later G-Clarons -- with very low distortion and usually reasonably sharp. Double Gauss type process lenses seem to be in the minority; tessar types, dialytes, and, yes, plasmats are much more common.

I'm tempted to suggest that a 4/4 double Gauss process lens will be relatively wide angles as process lenses go 'cos there are some fine 4/4 double Gauss wide angles for general photography. Am held back by, e.g., some Soviet process lenses in the RF- series -- I have a 450/10 RF-10 -- that are 6/4 double Gauss with claimed coverage of 43 degrees.

I have the impression that 25" process lenses typically cover around 45 degrees. Yours may differ. But 45 degrees and 25" mean a 21" circle. If so, really tight on 14x17 and 8x20 at infinity, not enough for 16x20. Yours may differ.

[Dan Dozer]

Hi Dan,

Thanks for the detailed description. It definitely is the 4/4 Double Gauss based on your diagram. The only time I've used it so far is for closer than infinity (portrait type work) and it easily covered the 8 x 20. Not sure about infinity - I'll have to put it on the camera and check it out.