Fixing Discolored Radioactive Glass
Rear element of a Super-Multi-Coated Takumar (1971) 6x7 105mm f2.4 is turned a yellow amber color.
The rear element is radioactive, for sure. This is what caused the discoloring. Based on researching the interweb it sounds like most lenses that are hot, it was the rear element that is thoriated. On this lens there is no radiation admitted anywhere but thru the rear of the lens. It's pretty much all alpha.
You can get the discoloration to go away for a while by exposing to UV light. Some say any LED light will do (an IKEA desk lamp is popular). What I don't get is if the rear element is the bad one, why do they project the light through the front of the lens? It looks as if a lot of lenses of that era have a yellowish reflection of the front element. are they confusing this with discoloration of the glass?
Would something bad happen if I projected thru the rear element?
Has anyone done this- cleared up the discoloring?
I have never done this with a lamp. You can buy lights that are just UV (usually for plants and stuff) and that would probably be faster. I don't know how long it would take with a normal lamp. I haven't owned a yellow takumar in a while, but last time I did I set it in a window sill to get some sunshine. This kinda depends what your house setup is like whether that would work or not.
I see no reason why going through the rear would cause any issues. Maybe if the coating is on the front element, it would be more efficient going from the front? It's passing through anyway, so I wouldn't think that would matter.
Quote from James Warner on December 6, 2023, 12:36 pmI have never done this with a lamp. You can buy lights that are just UV (usually for plants and stuff) and that would probably be faster. I don't know how long it would take with a normal lamp. I haven't owned a yellow takumar in a while, but last time I did I set it in a window sill to get some sunshine. This kinda depends what your house setup is like whether that would work or not.
I see no reason why going through the rear would cause any issues. Maybe if the coating is on the front element, it would be more efficient going from the front? It's passing through anyway, so I wouldn't think that would matter.
I am leery about leaving it unattended in a window. I am really paranoid about somebody (like a certain feline) breaking it indoors. That would be bad. I bought that IKEA lamp and left it on for two days and didn't really see a change. I decided that this lamp was actually pretty nice and I didn't want to fry it out. I am probably going to just take it outside and leave it in the sun on nice days. Also one guy on YT says he likes the warmer effect the lens has on his photos with the lens untreated. Maybe it's worth exploring that.
Incidentally, I have a connection where the lens got tested (I don't want to say where) with equipment not available to the public. The guys who tested it went above and beyond what I asked, I think they found it really interesting. The lens is giving off alpha at levels consistent with what you read on the web. It's also emitting small amounts of beta and gamma. Really small but above background.
No measurable radiation could be detected from the front of the lens. All the readings were tested from the exposed real element 1/4" away.
They also figured out that in addition to thorium, the glass has traces of radium and potassium. If I remember right the radium was emitting beta and the potassium, gamma.
Quote from KankRat on December 6, 2023, 6:55 pmQuote from James Warner on December 6, 2023, 12:36 pmI have never done this with a lamp. You can buy lights that are just UV (usually for plants and stuff) and that would probably be faster. I don't know how long it would take with a normal lamp. I haven't owned a yellow takumar in a while, but last time I did I set it in a window sill to get some sunshine. This kinda depends what your house setup is like whether that would work or not.
I see no reason why going through the rear would cause any issues. Maybe if the coating is on the front element, it would be more efficient going from the front? It's passing through anyway, so I wouldn't think that would matter.
I am leery about leaving it unattended in a window. I am really paranoid about somebody (like a certain feline) breaking it indoors. That would be bad. I bought that IKEA lamp and left it on for two days and didn't really see a change. I decided that this lamp was actually pretty nice and I didn't want to fry it out. I am probably going to just take it outside and leave it in the sun on nice days. Also one guy on YT says he likes the warmer effect the lens has on his photos with the lens untreated. Maybe it's worth exploring that.
Incidentally, I have a connection where the lens got tested (I don't want to say where) with equipment not available to the public. The guys who tested it went above and beyond what I asked, I think they found it really interesting. The lens is giving off alpha at levels consistent with what you read on the web. It's also emitting small amounts of beta and gamma. Really small but above background.
No measurable radiation could be detected from the front of the lens. All the readings were tested from the exposed real element 1/4" away.
They also figured out that in addition to thorium, the glass has traces of radium and potassium. If I remember right the radium was emitting beta and the potassium, gamma.
That is really interesting and cool you were able to have some people test it!
I will add that I shot several Takumar's without treating their yellowness and it was fine. None of mine were ever that bad anyway, but the slight tint never seemed to bother anything. It's either like a Tiffen 812 warming filter effect going on, or you can just counteract it in post. I know technically it would be filtering certain wavelengths of light, but it just never seemed like a big deal and you wouldn't be able to tell in the final images.
Overtime with enough sun exposure it should theoretically reduce it significantly.
Quote from James Warner on December 7, 2023, 2:44 pmQuote from KankRat on December 6, 2023, 6:55 pmQuote from James Warner on December 6, 2023, 12:36 pmI have never done this with a lamp. You can buy lights that are just UV (usually for plants and stuff) and that would probably be faster. I don't know how long it would take with a normal lamp. I haven't owned a yellow takumar in a while, but last time I did I set it in a window sill to get some sunshine. This kinda depends what your house setup is like whether that would work or not.
I see no reason why going through the rear would cause any issues. Maybe if the coating is on the front element, it would be more efficient going from the front? It's passing through anyway, so I wouldn't think that would matter.
I am leery about leaving it unattended in a window. I am really paranoid about somebody (like a certain feline) breaking it indoors. That would be bad. I bought that IKEA lamp and left it on for two days and didn't really see a change. I decided that this lamp was actually pretty nice and I didn't want to fry it out. I am probably going to just take it outside and leave it in the sun on nice days. Also one guy on YT says he likes the warmer effect the lens has on his photos with the lens untreated. Maybe it's worth exploring that.
Incidentally, I have a connection where the lens got tested (I don't want to say where) with equipment not available to the public. The guys who tested it went above and beyond what I asked, I think they found it really interesting. The lens is giving off alpha at levels consistent with what you read on the web. It's also emitting small amounts of beta and gamma. Really small but above background.
No measurable radiation could be detected from the front of the lens. All the readings were tested from the exposed real element 1/4" away.
They also figured out that in addition to thorium, the glass has traces of radium and potassium. If I remember right the radium was emitting beta and the potassium, gamma.
That is really interesting and cool you were able to have some people test it!
I will add that I shot several Takumar's without treating their yellowness and it was fine. None of mine were ever that bad anyway, but the slight tint never seemed to bother anything. It's either like a Tiffen 812 warming filter effect going on, or you can just counteract it in post. I know technically it would be filtering certain wavelengths of light, but it just never seemed like a big deal and you wouldn't be able to tell in the final images.
Overtime with enough sun exposure it should theoretically reduce it significantly.
This lens is more amber/brown than yellow. Probably holding significant light back.
Quote from KankRat on December 1, 2023, 1:15 pmRear element of a Super-Multi-Coated Takumar (1971) 6x7 105mm f2.4 is turned a yellow amber color.
The rear element is radioactive, for sure. This is what caused the discoloring. Based on researching the interweb it sounds like most lenses that are hot, it was the rear element that is thoriated. On this lens there is no radiation admitted anywhere but thru the rear of the lens. It's pretty much all alpha.
You can get the discoloration to go away for a while by exposing to UV light. Some say any LED light will do (an IKEA desk lamp is popular). What I don't get is if the rear element is the bad one, why do they project the light through the front of the lens? It looks as if a lot of lenses of that era have a yellowish reflection of the front element. are they confusing this with discoloration of the glass?
Would something bad happen if I projected thru the rear element?
Has anyone done this- cleared up the discoloring?
Every vintage lens has characteristics, even on Takumar with Thorium Glass. So, I never think to discolored warm tone of radioactive glass.
I have compare Takumar 55mm F1.8, and satisfied with Auto Takumar 55mm F1.8. It has bolder yellow coating than others.
This is entirely too much character for my taste.
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