Schneider Xenotar 150mm f2.8 Lens Question

[ColonelKurtz]

Hello,
Was wondering if anyone can help me. I recently acquired a Schneider Xenotar 150mm f2.8 lens, and see that the rear element is quite yellow. I'm gathering that this is from age, and/or the thorium present in this mid-1950's version. I have two questions. Is the proper way to keep this lens open for focusing achieved by setting the lens on "B" and holding it open with a cable release? 2nd Question: Will placing the rear element of this lens in sunlight clear the yellow from it? Any help is greatly appreciated. Thanks

[Corran]

Proper way of keeping the lens open for focusing depends on the shutter. These came in different shutters, so you'll have to let us know what shutter you have. However, using a locking cable release on B certainly is one option that is available - your shutter may also have a little tab that keeps the shutter open when pressed and fired.

As for the yellowing - UV light will clear it (with time) so leaving it in a sunlit area is a possibility, just don't leave it in the rain . I also at one point tried a black light, which worked but was very slow. These will have differing amounts of UV light depending on the bulb I believe.

[Pere Casals]

Will placing the rear element of this lens in sunlight clear the yellow from it?

You may also place a UV light LED source inside the box, in some 6 months you may remove 80% of the yellow stain.

[ColonelKurtz]

Thanks guys... This one has a compur shutter. Looks like the yellowing is in the rear element only. Will put the rear element in the sun throughout the day.

[Jac@stafford.net]

Thanks guys... This one has a compur shutter. Looks like the yellowing is in the rear element only. Will put the rear element in the sun throughout the day.

Pardon my ignorance and over-concern but even here in Minnesnowta the summer sun can bake anything. Is there any possibility that the heat could loosen part of the rear element?

(Funny but I just retrieved my gold watch from outside and it was blistering hot. Silly me.)

[ColonelKurtz]

I was concerned about that, as well, although the temp here in Los Angeles is very mild, at the moment, with some wind... Not gonna leave out too long though. I've heard from some that it works, and from others that its "snake oil", although there are several possibilities for yellowing, so I'm not gonna rule anything out, just yet. I might try a high intensity LED bulb from Home Depot, but in the end may have to live with the yellowing, which is fine as well.

[Corran]

The UV light is what "cures" the staining. Depending on the amount of UV that reaches you, results may vary. With the amount of air pollution in LA, you might have a problem with UV scattering...

[Dan Fromm]

OP, re whether UV treatment is "snake oil," I've had four lenses with radiation damage. Three TTH Apo-Tessar clones and one Repro-Claron. All cleared after being basking for several months under a 20w BLB compact fluorescent. Dim bulb, took a while to do the job but eventually it did it.

[ColonelKurtz]

Yeah "snake oil" doesn't really make sense to me, as one can easily see that the yellow is either disappearing, or its not. I've read of other people's lenses turning yellow because of the various chemicals in the lenses changing composition over time (balsam, cement between glass, etc... etc...), and no amount of uv "curing" those lenses... on and on... will see what happens. Thanks

[EdSawyer]

get a UV LED flashlight, you can clear it in a few weeks that way.