Thank you very much, David.
Best regards,
Peter S
On Apr 13, 2021, at 9:13 AM, David Young <dsy@xxxxxxxxxxxxx> wrote:
Good morning, Peter!
A number of older lenses had thorium, a weakly radioactive element, in their
glass. It turns the glass yellow, over time.
I've had a couple of the Super-Takumar 50/1.4 (still have one!) and they're
nice lenses to use. Though if yellowed, the colour balance can be odd. Yes,
putting them on a windowsill that gets lots of direct light, will clear them
up. Be aware, however, that the process is slow, and they may have to be
left there up to a year, perhaps more, depending on the yellowing. Just
remember to rotate them a 1/4 turn, every month or so, to avoid parts of the
glass being in the shadow of the lens barrel!
That being said, noticeable yellowing is unlikely to reoccur in a further
decade or so. But, eventually it will yellow again.
See:
https://en.wikipedia.org/wiki/Thoriated_glass
https://camerapedia.fandom.com/wiki/Radioactive_lenses
https://petapixel.com/2018/06/07/a-radioactive-lens/
Hope this helps.
David.
Good morning to everyone. I ran across a sentence in an eBay
description of a Asahi Pentax Super Takumar lens that caught my
attention, and I'm wondering if anyone can confirm it or debunk it.
In describing the lens the seller goes through the usual things but
then adds in their last sentence: "There is some yellowing of the
elements as is common with these lenses - exposure to UV light will
clear it up."
https://www.flickr.com/photos/159388964@N08/51113154709/in/dateposted/
Is that true? And would the UV light being referred to just be
sunlight or would it need to light filtered in some way to
concentrate the UV part of the spectrum?
Thank you.
Best regards,
Peter S ------
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