G-Clarons (again)

[Luca Merlo]

Somebody in the net claimed that the G-Clarons lenses, due to they symmetrical design, easly convert into lenses of other focal lenghts only replacing the front cells. This could be possible using adapters sold by Grimes plus the usage of a yellow filter. Since I own a 150, 240, 305 g-clarons I am quite interested into the matter since it would greatly decrease the bulk of my my gear. Do you know anything about this possibility ? What are the results ?

[John O'Connell]

I believe that the net speculation is that Ron Wisner's convertible set was a bunch of G-Claron elements. I'm not sure I believe that.

Glennview has tried to sell mismatched Computar elements as "never-produced" Computar focal lengths. You could contact him about the Computar mismatches to see how they worked out.

[Dan Fromm]

Luca, bug Jim Galli. He's reported using dagor type G-Clarons as convertibles and swapping cells among them.

I'm not sure about plasmat type G-Clarons, but I believe that Meyer sold casket sets of plasmat cells. There's a hint.

Why don't you swap some of your lenses' cells around and see how well they shoot? The only constraint is that the cells you swap have to fit the same size shutter or barrel.

[Luca Merlo]

John and Dan thanks a lot for your quick answer. I will try to contact Jim about it (where are you Jim by the way ?). I am still wondering about the principle behind that though. How could I transform a 305 lens in a 610 one ? And in principle with the three focals that I have (150, 210 and 305), how many focals could I compose ?

I have found an old Wisner convertible plasmat brochure and it is describing the 4x5 Set to be made of these "five polished brass cells: 250, 250, 350, 400 and 450". So it seems to me that the speculation is groundless ..........

Best regards and Ciao from Italy

[Ole Tjugen]

A symmetrical lens consists of two equal lens cells, the focal length of each cell being a little less than twice the focal length of the whole lens.

Removing the front cell of a 305mm would give you something like a 580mm, not a 610mm (just guessing, but it's in that area).

The general equation is: 1/F = (1/f1 + 1/f2 + d) where d is a correction dependent on spacing, f1 and f2 the focal lengths of the components, and F the total focal length.

[Luca Merlo]

Many thanks Ole. Stay warm upthere ;)

[Dan Fromm]

Um, come to think of it, Luca, Boyer Zircons (6/4 plasmat taking lenses, contemporary with Symmars) were sold as convertible. Rear cells alone were f/12, roughly 1.8x the combined focal length. The same was true of Symmars.

So be a nice person and go ask your lenses what they can do for you. When you've done the experiment and know, share what you learned with us.

But remember, your 150 goes in a #0, your 240 and 305 go in a #1 (see http://www.schneiderkreuznach.com/archiv/pdf/gcn_82.pdf ) so the swaps you can do are a little limited. Rear of 240 with rear of 305, and vice versa. Also, please check whether each of your lenses' cells have roughly the same focal length.

[Ole Tjugen]

With Symmars, the rear cell is approximately 1.7 times the focal length, the front cell around 1.9 (q.v. the 300/500 Symmar convertible). Boyer Zircons had a slightly different "power distribution".


This is yet another thing on my growing list of "things to try". Symmar 100 and 135 (#0); 150, 180 and 210 (#1), 240 (#2), 300 (#3); and G-Claron 210 (#1) and 355 (#3); as well as Angulon 90, 120 (#1), 165 (#2) and 210 (#3).

Yes, the Angulons were originally sold as convertible. Focal lengths are 1.5 (rear) and 1.8 (front) times total focal length - or at least that's what they were in the 1930's.

[sanking]

Yes, the Angulons were originally sold as convertible. Focal lengths are 1.5 (rear) and 1.8 (front) times total focal length - or at least that's what they were in the 1930's.

Dagors were also once sold as convertible. However, the single element is not as well corrected as the two together. You can improve performance quite a bit in B&W by using an orange filter.

Sandy King

[Jim Galli]

Instead of asking, go make some pictures with your conversions and report back. I have a 210 - 240 dagor type. The front is from a 240 and the rear is from a 210. It focuses at 225mm, covers 8X10 much better than the normal 210 does, and is one of the sharpest lenses I own. Combining the 150 and the 305 will give you something in the 200+ range that won't be as good as what you already have from the factory. Your 240 and 305 combined might give an excellent 270ish mm lens. Try it. Tell us. Best to you.

Oh, I didn't do my cobble on purpose, it was on ebay that way and no one would bid. I surmised that Schneider had already done that anyway with their early triple convertible Symmars of 1952 or so. So I bought it for $48. It ain't for sale.

[Steve Hamley]

Come on Jim,

I'll give you $49 for it! :D

Steve

[Luca Merlo]

Thanks Sandy and thanks Jim. I will try and I will report.

Best regards from Italy