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03-14-2012, 06:08 PM   #31
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QuoteOriginally posted by ChrisPlatt Quote
I once owned a Super Takumar 35mm f/2.0 lens, the later version with 49mm filter thread.
The lens elements had turned so deeply amber I dared not use it for color slides.
But it was fine for use with black and white film - a built-in yellow filter of sorts...

Chris
yea, that would not fly with my Portra. I shy away from purchasing any lens that has yellowed, personally. even if UV bleached it will eventually re-yellow, so whats the point of buying a lens that will one time become slower in light gathering capabilities? and the 8 element takumar 50 has always been reported as performing slightly worse than he later version, despite it being made to be a planar killer. I doubt my Zeiss was worth the cost over even a super clean takumar 50, but I feel more comfortable knowing it won't yellow or give me a dose of radiation larger than normal background levels, which is petty scary when one considers how much the lens is in front of my face.

03-14-2012, 06:49 PM   #32
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QuoteOriginally posted by stevebrot Quote
I researched this matter several years ago and based my comment partially on that research and partially on what I have been by various camera buffs, repair people and such. If the 55/1.8 has the yellowing problem, it was new to me.






On the other hand, I have long suspected that the lists (including the one linked several comments above) are far from complete. I just did a little Google work and was surprised to find videos of people testing lenses that I would never have dreamed were radioactive. Based on that search it appears that these lenses were quite common. The big surprises? How do these sound:
  • Yashinon DX 35/1.8 (on Electro 35 CC)
  • Various Super-8 movie cameras
  • Yashinon DS/DX 50/1.4/1.7
  • Mamiya/Sekor 55/1.4
  • Leitz Summicron 50/2 (collapsible ca. 1953)
  • A plethora of Canon FD/FL fast 50s
  • EBC Fujinon 50/1.4
  • Various Zeiss Jena
...and yes...at least two (SMC and S-M-C) Takumar 55/1.8.

It almost makes me want to get a cheap geiger counter and head down to check out the shelves at the local used camera places. Seriously though, I own a couple of lenses (non-Pentax fast 50s from the late 60s and my Jupiter-8 in Contax/Kiev) that have a yellowish cast that I would sort of like to test just to satisfy my curiosity.


Steve
Some Pentax 55/1.8 Takumars are radioactive and some aren't. My early 55/1.8 Auto Takumar isn't radioactive at all, but the S-M-C 55/1.8 is about 2/3 as radioactive as the famous 50/1.4 S-M-C Takumar, based on a Geiger-Mueller pancake probe close to the rear element. Farther away, as measured with a "high energy" gamma ray scintillator probe 100mm from the side of the lenses, the 55/1.8 is only about 20% as radioactive as the 50/1.4.

The 55/1.8 is not significantly yellowed, while the 50/1.4 was decidedly yellow, before I gave it the UV treatment.

The most surprising finding with the geiger counter was that the Canon FD 17mm f/4 and Olympus 20mm f/3.5 bellows lenses are both radioactive.

BTW -- Does anyone know of a comprehensive list of thorium-containing lenses?
03-14-2012, 07:41 PM   #33
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what would make the takumar 50 more radioactive than a possible takumar 55? more thorium in the glass? if the Takumar 50 is known to be thoriated and thus yellows quite a lot over time, but a takumar 55 also reads as radioactive beyond background levels and also displays yellowing but on a lower level for both, what is the difference? and what would be gained be a less thoriated lens? I would assume that they would be given the same treatment for the same purpose. I don't dispute that there are likely thoriated 55's and there seems to be plenty of evidence to back that up, but I just don't understand why one would be more so than another if it was for the same ultimate goal of lower dispersion levels. its strange to me that there are 55's and apparently other lenses that seem to be thoriated but clearly not on the same level as the 50 1.4.
03-14-2012, 07:57 PM   #34
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QuoteOriginally posted by séamuis Quote
what would make the takumar 50 more radioactive than a possible takumar 55? more thorium in the glass? if the Takumar 50 is known to be thoriated and thus yellows quite a lot over time, but a takumar 55 also reads as radioactive beyond background levels and also displays yellowing but on a lower level for both, what is the difference? and what would be gained be a less thoriated lens? I would assume that they would be given the same treatment for the same purpose. I don't dispute that there are likely thoriated 55's and there seems to be plenty of evidence to back that up, but I just don't understand why one would be more so than another if it was for the same ultimate goal of lower dispersion levels. its strange to me that there are 55's and apparently other lenses that seem to be thoriated but clearly not on the same level as the 50 1.4.
Absorption rate of the materials used is variable based on a number of factors as is the decay/ clearing rate. If the glue, as has been suggested, is the culprit and its an interaction between the radiation applied and the volumn of materials then the amount of glue may be the key to the differences you are puzzled by.

03-14-2012, 08:21 PM   #35
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QuoteOriginally posted by Docrwm Quote
Absorption rate of the materials used is variable based on a number of factors as is the decay/ clearing rate. If the glue, as has been suggested, is the culprit and its an interaction between the radiation applied and the volumn of materials then the amount of glue may be the key to the differences you are puzzled by.
but why would a 50 have inherently more optical bonder than a 55 if the thoriated glass was only the rear element. the 50 and 55 have similar optical formulas and both have a single rear element group (one lens in one group) I would imagine their wouldn't be a significant difference here in the material that reacts with the decay of thorium.
03-14-2012, 09:47 PM   #36
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QuoteOriginally posted by séamuis Quote
what would be gained be a less thoriated lens?
...fewer thoriated elements?

I was surprised to see on some of the videos that sometimes it is the front element. Other times the rear, and sometimes the whole bleeping lens.


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03-15-2012, 01:34 AM   #37
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QuoteOriginally posted by séamuis Quote
but why would a 50 have inherently more optical bonder than a 55 if the thoriated glass was only the rear element. the 50 and 55 have similar optical formulas and both have a single rear element group (one lens in one group) I would imagine their wouldn't be a significant difference here in the material that reacts with the decay of thorium.
UV is an enemy of the kind of radiation you are talking about, so if one lens were exposed to significantly more direct sunlight that could account for two similar items giving off different readings.
03-15-2012, 02:56 AM   #38
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QuoteOriginally posted by séamuis Quote
what would make the takumar 50 more radioactive than a possible takumar 55? more thorium in the glass? if the Takumar 50 is known to be thoriated and thus yellows quite a lot over time, but a takumar 55 also reads as radioactive beyond background levels and also displays yellowing but on a lower level for both, what is the difference? and what would be gained be a less thoriated lens? I would assume that they would be given the same treatment for the same purpose. I don't dispute that there are likely thoriated 55's and there seems to be plenty of evidence to back that up, but I just don't understand why one would be more so than another if it was for the same ultimate goal of lower dispersion levels. its strange to me that there are 55's and apparently other lenses that seem to be thoriated but clearly not on the same level as the 50 1.4.

The glass elements in the 50/1.4 are larger than those in the 55/1.8. This may account for some or all of the difference?

The degree of yellowing seems to be weakly related to the level of radioactivity. Other factors could be age, glass composition, prior de-yellowing, being stored in the dark vs light, and perhaps even the glue?

My yellowest lens if tjhe Leica 50mm f/2 collapsible Summicron, followed by the 50/1.4 Takumar before de-yellowing. My two most radioactive lenses are the Canon FD 55/1.2 Aspherical and 50/1.4 early M42 Fujinon, and they are only slightly yellow.

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