Unknown lens configuration

[swmcl]

G'Day,

So far I'm unable to determine the lens type for a lens recently acquired. I'm wondering if I may get a clue or two.

I have made a diagram of the 4 elements roughly showing their relative curvatures.

I think I can rule out a triplet design and a tessar.

It's not a symmetrical type either.

Any help much appreciated.

Cheers,

[Math]

If you'd flip it it looks a bit like an unar (http://commons.wikimedia.org/wiki/File:Unar.svg\)lens.. I'm no optics expert however. Aren't there any markings on the lens?

[swmcl]

Hi,

Yes it looks a little like an unar in design but for the third element from the front.

It is an old lens in a brass barrel and it does have an aperture stop. The 4 elements are definitely in 4 groups. I am not going to get the actual glass out from their respective holders so I can't say it is only 4 elements. It might have 6 for all I know.

I wonder if it could be some sort of portrait lens design?

I wonder ...

What is the layout / design of the Visual Quality IV and Cooke PS945 ?

I wish!

Rgds,

[Steven Tribe]

Perhaps an Unar if the two rear lenses were switched? Just pre-tessar.

[walter23]

Almost looks like this "Pan-Tachar F", except for the rearmost element which is biconvex in this case:

http://dic.academic.ru/pictures/wiki/files/52/33a1399d14fdb9f9ebfcdd6fd556d025.jpg

[swmcl]

I should say that the elements are around the same diameter. If there is any difference then it would be quite small.

There is also no chance of changing the order in which the elements are placed in the barrel. There's only one way to re-asemble this one.

It looks as though I'll have to raise the reward to at least 100 jelly beans!

Rgds,

[Steven Tribe]

Perhaps a copy of the portrait Unar - without the soft focus adjustment?

[swmcl]

Umm what's a portrait unar look like (design-wise)?

I'll do a search ...

Cheers,

[Steven Tribe]

Dallmeyer changed the petzval rear set design for his soft focus objective (which, incidently, look very much your rear set!) . I don't have a layout for the Portrait Unar. Check for rear adjustment. By that I mean, can the rearmost lens be screwed out and change the distance to lens no.3?

[swmcl]

The only way to adjust it would be to unscrew one lens with respect the other. I'll make another check but there is no adjusting ring of any sort.

The front two elements are as one in a set and so too the rear. The two sets unscrew from the barrel.

Cheers,

[Paul Fitzgerald]

"Umm what's a portrait unar look like (design-wise)?"

the Portrait Unar has the same layout as an Unar, with a moving second element. If it is an Unar than the rear cell would work alone as a really soft focus, slightly shorter FL lens.

[Bernard Kaye]

UNAR but for reversal of rear two elements but there was a T. T. & H. f 2.5 lens that had the simple back of the Triplet replaced by two glasses. "OPTICS" by Arthur Cox, Seventh Edition, page 163, discussed page 162. If this is it, this is a credible drawing.

Bernie Kaye

[swmcl]

And I believe an unar would be good for .... ?

I'm not in a position to test it yet. The local machinist is upgrading his CAD lathe.

Thanks all.

[Bernard Kaye]

Sincerely, Good for fun & joy in taking pictures.
Bernie

[Bernard Kaye]

In the Cox book Optics, the drawing of the TTH on page 163 is remarkably close to your drawing.
Bernie

[Bernard Kaye]

In "A History of the Photographic Lens," by Rudolph Kingslake, Academic Press, Inc., Copyright 1989, (not revised book to be issued perhaps January 10th,) on pages 108-110 is discussion and diagram of The Speedic Lens by H. W. Lee, that also was in the Cox book that I mentioned on January 3rd, same perhaps as yours. You may have an unusual if not rare lens.
Bernie Kaye