Re: [Leica] 85mm f2 Russian now a question of Thorium glass

[P2CON@aol.com]

Don, and other interested parties,

I have an example of each; the LTM version, made by KMZ in 59, and the 
Kiev/Contax mount, made by LZOS in 61. Both show a very yellow reflection from one 
of the interior elements, along with a pale yellow/white behind and in front of 
it and the very bright purple reflection from the front element. These two 
lenses from two different factories show the exact same reflections when held 
against the light. When looking through them at a white sheet of paper there is 
a slight yellowish cast to the image. I have never noticed any effect on an 
actual photograph taken with either lens, apparently the yellowing is not 
sufficient with my examples to be noticed, or else I am not that color critical.

My experience with glass yellowing badly is with the Pentax Super Takumars. 
The Pentax enthusiasts have discovered that the yellowing can be reversed by 
soaking the lens in direct sunlight for a couple of weeks. I did try this with 
one really bad 35mm/f2 that was unusable with color film due to the yellowing. 
Two summers ago I put it out on the patio with the sun shinning directly 
though it. I wrapped the lens barrel with aluminum foil so that the sun light was 
reflected back through it and pretty much kept it oriented so the sun was 
shinning in on the lens axis. I quit the experiment after about ten days with the 
yellowing pretty much gone. Just now I took it outside with one of the Soviet 
85/2's and checked both against a sheet of white paper. The Super Takumar still 
shows less yellowing that the Soviet lens. As I said before, there is no 
obvious color effect on film with the 85's, but maybe next summer I will try the 
sun soaking trick on them anyway.

Perhaps some of you with yellowed Summicrons have tried this trick. Anyone 
willing to tell us about it?

Regards, Paul Connet


<< Don writes:
<< Karen,
You make an excellent point and I have some older lenses where the
balsam is clearly yellowing.  However, this particular lens has at least
one very yellow element, probably the thick center element in the
triplet of a sonnar design.  In this case, far more yellow than the one
in my very early Summicron or in any of the aero Ektars I have seen.

I have only seen one other lens almost this yellow and that was one of
the early production Canon 35 F2 FD lenses.

Don >>
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