Lens order on triple convertible

[j.e.simmons]

I have three triple convertible lenses - two B&L Protars and a Rapid Rectilinear probably made by B&L. All of them came to me with the lower length lens on the front and the longer on the rear when combined. For instance the RR has the 20” on the front and the 28” on the rear. All of the B&L catalogs I’ve seen show the longer element as the front element when combined. Which is right, and does it really make any difference?

[Greg]

My 12 3/4" B&L Protar Series VII came with the 18 7/8" group in the front and the 27" group in the rear. For all the Protars that I have owned, the longer group was always in the back. Now on my Wollensak 13" Series IA Raptar in its OEM Alphax, the 25 1/2" group is mounted in the front and the 20" in the rear. My Wollensak literature states that if using a single group, it should be behind the iris.

[j.e.simmons]

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.

[Jim Noel]

My triple converters have all had the shorter focal length in the front. When a single element is to e used, it is always laced in the back.

[David Lindquist]

My circa 1930's Zeiss catalogue shows for the Protar the longer focal length cell goes in front and the shorter focal length cell goes in back. When a single cell is used it goes in the back. It doesn't say why for either case. It's always been my understanding that for the single cell the corrections are better when the cell is behind the aperture.

Checked Cooke's website. For their Series XVa Convertible they show the 645 mm cell goes in front and the 476 mm cell goes in back. Couldn't immediately find any statement as to where the single cell should go.

Just took another look at the Cooke website. In addition to giving the filter sizes for the two lens cells they give this: "Filter Size - Shutter Front". This suggests to me that they intend that the single cell goes on the back of the shutter and then a filter can be mounted on the front.

David

[Jim Fitzgerald]

To use the single component on the Cooke XVa it goes on the back. You are right in that the 19" component is on the back and the 646mm is on the front when both are used giving you 312mm. No doubt about this one as I'm looking at mine.

[j.e.simmons]

Just to be clear, I’m asking about the combined elements and whether it makes any difference which is in front.

[Louis Pacilla]

Just to be clear, I’m asking about the combined elements and whether it makes any difference which is in front.

Most manufacturers suggested when used combined the strongest/longest FL is in front of shutter and weaker/shorter FL behind. I have loads of different triple convertible from Wollensaks 1/1A's, Gundlachs Turnner Reich, Zeiss/B&L Viia's amd all have it this way.

[Kevin Crisp]

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.

[Paul Ewins]

The triple convertible Schneider Symmars had the longer focal length at the front as did the Angulons.

[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.