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04-14-2012, 09:44 AM   #1
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Super Takumar 35mm f2 (49mm) yellow coating

I'd like to use this lens through an adapter with my Nex 5, is the yellow coating I see on the front lens "real coating" or should be neutral to avoid yellow colours on pictures to take?
Thanks all for support, my Pentax days are so far (my first SLR was a black Asahi Pentax Spotmatic II with the Takumar 28mm f2.8, the 50mm f1.4 and the 135mm f2.8).
Cheers

04-14-2012, 10:26 AM   #2
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Sounds like it could be yellowing from thorium glass. This is fairly common in Super Tak 50mm f/1.4, less common in other lenses of that era. If I understand it correctly they added thorium to the glass mix to improve optical properties but did not consider what the slight radioactivity of the thorium would do over 40 plus years. Here is a link with additional information.

This can be corrected by applying UV light to the lens. Some have used a UV light but direct sunlight works as well, though slower. Search on "fixing yellowed takumar" and you should get a bunch of solutions.

Here is one that seems to work quickly.

But on modern cameras it is not a huge problem as any slight color can be adjusted by changing the WB in PP. Though if it is too severe it can change the metering a bit. Again not a big problem on modern cameras just adjust the EV to compensate.
04-14-2012, 10:33 AM   #3
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I believe the ST 35/2 was subject to yellowing and is easily cured with UV light or sunlight, as the 50/1.4 method.
04-14-2012, 11:44 AM   #4
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The other thing to consider is that unless the yellowing is severe, it's not necessarily detrimental. It can have a very slight warming effect on your shots, but it's not drastic, and could be considered a quality.

04-14-2012, 12:11 PM   #5
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Thanks a lot!
04-15-2012, 01:54 AM   #6
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Just FYI ...

Bojour,

Here's a thread that I launched a while back ... might be helpful to you. Also, I plan to buy the IKEA lamp in the near future ...

https://www.pentaxforums.com/forums/pentax-film-slr-discussion/178841-yellowi...-55-1-8-a.html

Salut et bon courage, John la "Green" Grenouille
04-15-2012, 04:51 PM   #7
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Are you seeing a yellow tint when looking through the glass or a yellowish reflection from the coatings on the surface of the glass? A yellow tint looking through the glass is due to discoloration of the balsam cement used to bond the grouped glass elements together. Often, this is caused by low-level radiation from thoriated glass acting on the balsam. That can be "cured" by treating the lens with U.V. or strong sunlight.

If you are seeing a yellowish reflection from the surface, that is typical for many coated lenses of the time and is true for the four Super-Takumar lenses I have in my possession. It is normal and good.


Steve
04-15-2012, 04:57 PM   #8
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QuoteOriginally posted by stevebrot Quote
A yellow tint looking through the glass is due to discoloration of the balsam cement used to bond the grouped glass elements together. Often, this is caused by low-level radiation from thoriated glass acting on the balsam
Really? I thought it was a change in the glass itself, due to the thorium. It's a neat phenomenon, either way.

04-15-2012, 05:20 PM   #9
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QuoteOriginally posted by Philoslothical Quote
Really? I thought it was a change in the glass itself, due to the thorium. It's a neat phenomenon, either way.
I have heard both ways, though the "tanning" of the balsam sounds a lot more probable from a chemist's perspective.


Steve
04-15-2012, 05:44 PM   #10
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Cool. Thanks, I'll read more on that sometime.
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