Converting a Sironar-N?

[Jim Rice]

I tried just the rear cell on my 360 Caltar II-N and it formed an image that didn't look too sucky. I realize that I will lose a LOT of correction doing this and said lens is far from optimized for this stuff, but how bad would it be on film, really? Also, may I assume a 1.7 factor in focal length and f-number? Thanks, Jim

[John O'Connell]

I only ever did this with a 150 Sironar. Everyone has different standards, but I didn't do it again; low contrast, rather than sharpness, was the killer. I just guessed at 1.8 for the factor, but if you calculate the reproduction ratio you should be able to get ac accurate focal length with the Stroebel VCT formulas.

[Carsten Wolff]

Interesting. My "convertible" 240mm Sironar needs the rear group removed to work at the long end....(700mm in that case)...