Lens order on triple convertible

[David Lindquist]

I've always believed it was longest on the front, single element behind the shutter, unless that creates a bellows-draw problem (which is often the case) in which case use the single on the front and adjust for focus shift either way. Going from memory, Ron Wisner used to have an article on his website claiming that his optical bench testing got superior results with Protars with the shorter one in front. Or maybe it was single cells on the front.

Yes, I too had a recollection of Ron Wisner contradicting usual practice with Protars. Tracked down my source, the March-April 1993 issue of View Camera and Wisner's article on the history of Zeiss lenses. He says that contrary to the advice of Zeiss and Bausch & Lomb he places the longer focal length cell to the rear. He then asserts: "In computer analyses and bench tests we have found that almost without exception the larger lens being in the rear renders better correction for spherical aberration when used at infinity or similar magnification ratios."

I dunno, I don't have an optical bench or the computer programs/knowledge/skills to verify this so I'm going to continue to follow Zeiss's advice when using my Protar "C" set. When I get the chance I'll try it Wisner's way and see if I see a difference. That's simple enough to do.

David

[David Lindquist]

The B&L literature says the same - single element behind the iris. Interestingly, on the old Rodenstock Sironar double convertibles, the rear element was removed and the front remained in place when using a single element.

My guess, let me emphasize guess, is that Rodenstock calculated this lens so that using the single cell in front of the diagram worked well, or at least well enough. This has the advantage of not exposing the inside of the shutter so much when used this way and filters mounting to the front of the lens can still be used. I have a 1968 Rodenstock brochure where they describe the Sironar and how it's front cell only is used to give the longer focal length. I'm a bit surprised they don't point out these advantages compared to their main competitor, Schneider's Symmar.

David

[Kevin Crisp]

If you've tried it both ways with single elements and compared the negatives (at least on convertible Symmars and Protars) I really doubt you're going to see the difference. There is the dust issue. And it makes a significant difference in bellows draw that may turn go into no-go for some cameras.