Unmarked Brass Portrait Lens

[desertrat]

I bought this a couple of years ago on Ebay, and am now getting ready to mount it on the 8X10 Seneca. It's way too heavy and the flange is too big to mount on a lens board and hang on the front standard, so I will need to build some kind of a cradle to rest on the bed and slide the lens back into the front standard. If I install the extension rail and rack the rear standard back onto it, I should be able to focus the beast somewhat closer than infinity.

The lens is lacquered brass and completely unmarked except for the shell of a Wollensak Studio shutter No. 3, Style B. Some previous owner removed all the shutter's innards, so now it's wide open and shutterless. Checking the old Wollensak catalogs, the lens looks externally very much like a Series A (Vesta) No. 5., except the hood is longer.

But internally, I think it's different. I gather the Series A and later Vesta were Petzval types, but after taking the cells apart to clean all the surfaces, which it needed, the design seems to be different from a Petzval. I did some careful checking of reflections and curvatures, and this lens appears to be like an extra rapid rectilinear with an extra thin weakly positive meniscus element mounted next to the rear cemented doublet on the diaphragm side. This meniscus element is spun into it's own thin cell that screws into the back of the rear doublet cell, so it wasn't added as an afterthought. There is a faint hint of overall haze in the cement layers of both doublets that can be seen by shining a strong light on the doublets at a shallow angle and by looking through the doublets at a strong light source. It shouldn't be bad enough to seriously impair performance, but it does allow me to see the deeply curved cement interface in each doublet.

I drew a rough freehand sketch diagram, not to scale, but it should show the optical layout. I haven't found this in Kingslake or any other reference I can find.

Any ideas who might have made this lens or what type it might be?

[Jason Greenberg Motamedi]

The schematic looks a little like a Heliar, but it is much too long.

[Fotoguy20d]

Could it be a Vitax? I know the Vitax is a modified, soft focus petzval with adjustment. Is that the extra cell? If the FL is at the short end of what you estimate, you're right around f3.8

Dan

[desertrat]

I've never handled a Vitax, but they have an adjustment knob sticking out the side of the barrel. This one has no adjustment knob, no hole where one might have been, and no internal parts for an adjustment mechanism. The 'extra' cell screws into the back of the rear cell, with no markings for adjustment. I could probably get some kind of adjustment by unscrewing the extra cell part way, but I don't think it was designed to be adjustable.

[Jason Greenberg Motamedi]

The schematic looks a little like a Heliar, but it is much too long.

I reread what you described, and see that you said the middle element was positive, so I retract my statement, on a Heliar it is negative.

This is certainly not a Vitax, which is just a Dallmeyer type Petzval.

[Steven Tribe]

I would call this a Petzval - with a very complex and untraditional air-spaced pair. Perhaps an attempt to reduce the curvature of the focal plane? This was period when Voigtländer was¨"improving" the Taylor/Cooke triplet to the more complex Heliar.

[goamules]

Well then, I'd call it a Rapid Rectilinear with an additional simple miniscus added. Much closer to that.

[desertrat]

Thanks for the replies. There are people here who have worked with an awful lot of old portrait lenses, so I get a sense that this one was not manufactured in large numbers or commonly encountered, if at all. On a hunch, I took it apart again and did a rough check of the focus of the two doublets, focusing an image of trees in the distance through a window onto a wall. The doublets seem to have roughly the same focal length, and to the unaided eye the element curvatures that can be seen look about the same. I don't have a spherometer to measure the curvatures so all I can do is guesstimate. The single meniscus element was removed for this test. This seems to indicate the lens system was based on an extra rapid rectilinear with a single element mounted near the rear doublet. This could have been as an aberration corrector, or possibly an aberration introducer for soft focus.

It doesn't seem to be a soft focus type lens based on the limited testing I was able to do, more like a petzval or RR, sharp near the optical axis and soft at the edges. I won't really know until I get it mounted on the camera somehow. I'm working up a theory on how it might have been made, but someone here may have a similar lens and know more about its history, so I'll hold off on speculating for now.

Here is the lens with the cells disassembled. In the front row, left to right are the rear doublet, the meniscus element that screws into it, and the front doublet. The doublets can be screwed into either the front or rear of the barrel, but the cells are shaped differently so not interchangeable.


The lens assembled


Looking at the front. The reflections from the flash make the haze look really bad.


Looking through the lens at some objects on the kitchen counter. I think I see a slight amount of overall haze, but I think it will look better on the ground glass with the lens on the camera. There were bright kitchen lights behind me and I think some of that light got into the back of the lens while I was taking the image.

[goamules]

That's a strange one. If, indeed, the rear is a doublet and an air separated additional lens. Are you sure about that? Have you taken the glass out of the brass mount? The rear one I mean. Because a lot of petzvals just use the mount for separation, no metal ring. Which this looks like.

[Jason Greenberg Motamedi]

pretty big shade too...