Hazard a Guess - Mystery Lens

[Fotoguy20d]

Anyone have a thought as to what this convertible lens in a Compound #3 might be? There's no focal length indicated on the scale. First goes from f4.5-32, second from f8-64. There doesn't seem to be any marking on the barrel.

Thanks,
Dan

[paul ewins]

There are a few candidates; Goerz Dogmar, Steinheil Unofocal, Meyer Aristostigmat, although they were usually noted as being triple convertible. A Compound 3 would indicate something around 200mm/8". It is very unusual to see a front cell with no markings on it, almost like it was the rear cell in the wrong place. Does it have a filter thread?

[Rick A]

IIRC, Jason Brunner has a video that describes how to determine focal length and max aperture. What's on the reverse side of it, anything on the rear lens?

[Fotoguy20d]

It's from a not so local craigslist so before I drive 100 miles to check it out (it's attached to a 4x5 field camera so I'm not going just for a lens) I'm trying to figure out what it is. Seller was less than helpful - I'm going to ask again - maybe he can take a lok at the rear cell and send me a photo. Someone reversing the cells is very possible - I just got a T-R triple on the bay that was reversed.

Are the dogmar and unofocal convertible? I have a post-war 127mm dogmar in a raptar and a couple of 150mm unofocals in compurs - none have two scales - I'll need to check that out.

Dan

[paul ewins]

Sorry, that was a bit ambiguous, all three lenses I mentioned were advertised as being triple convertible. The thing is, all of them are f4.5 max aperture but f8 doesn't quite match any of the single cell values. The Dogmar is close, but that should be f8.5 using just the front cell or f6.8 using the rear cell. Another possibility is that the shutter is set up for two different lenses. B&L advertised (back in 1928) that they would fit lenses from other manufacturers to compound shutters that you bought from them. That cost $2 more than if you were using one of their own lenses. For another $1 they would engrave an extra aperture scale.

[Fotoguy20d]

The f8 marking isn't aligned with the f4.5. Maybe f6.8 would align with f4.5? It doesn't look like there's a filter thread.

[Fotoguy20d]

Very interesting. The rear is fitted with a coupling and a much smaller element (presumably f8) with a similar lack of marking.

[domaz]

I don't think the concentric circle machining you see on the inner rim of the lens is something that is on older lenses. It's probably some kind of modern (50s or newer) process lens mounted in a shutter. The first image also appears to be reflecting an unnatural green suggesting a coating.

[Sirius Glass]

If you take the two f-scales you can calculate a single solution for the focal length.

Steve