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06-25-2011, 12:17 PM   #16
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QuoteOriginally posted by tuco Quote
On the inside of one of my front bayonet Takumar lens caps it says "6x7 B" with plastic scratches around it just like in that picture. I think glass etching would look different too.
I only have one Tak, a 75mm and it says 6x7 B as well. My SMC lenses have pinch caps.

06-26-2011, 05:35 AM   #17
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I have to admit that Im beginning to doubt my own memory, was the cap on before I added the alu-foil to the front end? My cap has 6 X 7 A but they look different than the one on the foto. They protrude from the plastic and are not etched into it? I guess that if you guys where living in the vicinity you would expect a round of what we in Denmark call: »Kvajebajer« which translates to »The Jerks Beer«. Hmm? Im still not sure?
06-26-2011, 06:50 AM   #18
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From you picture, you can't tell whether it protrudes or is etched.

I just checked my 165mm with 6X7 A cap on. It looks very similar to your picture. See pic below. Note: on mine, letters protrude but you can't tell from pic either.

BTW, 6X7 A is for lens with 67mm filter size. 6X7 B is for 82mm filter size. They are both bayonet type.

Last edited by hyyz; 03-12-2013 at 10:36 AM.
06-26-2011, 11:34 PM   #19
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@hyyz: Hi, Im convinced that I must have had the cap on. Some how I really got myself fooled and I still can´t get it straight in my head, but your photo nails me flat to the ground, and thanks for clearing the puzzle up. Thanks a lot, and my excuses to anyone who I got fooled. Virtual beers all a round from me. Kind regards

06-27-2011, 06:30 AM   #20
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QuoteOriginally posted by Blue Quote
Oh flip! Hysterical
I repeat . . .
06-27-2011, 07:24 AM   #21
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QuoteOriginally posted by jt_cph_dk Quote
The UV light can reactivate the radioactive coating and thus remove the yellowing color
slight correction is needed here, High energy UV light actually bleaches the yellow colouration our of the lens coatings caused by alpha emissions from the thorium/lanthanum* glass.

I actually unscrew the rear lens cell from my takumars and directly expose them to UV light. borosilicate glass is a terrible transmitter of UV frequency light so isolating the yellowing lens speeds up the bleaching process considerably.


*Lanthanum on it's own isn't radioactive, but actinium which has many chemical and physical similarities is highly radioactive (half life = 21 years,beta particle emitter) and due to how closely related these two elements are they are very difficult to separate so many lenses that have lanthanum salts used in the glass can be radioactive.

Last edited by Digitalis; 06-27-2011 at 07:32 AM.
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