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12-13-2019, 02:01 PM   #16
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QuoteOriginally posted by steamloco76 Quote
ll you have to do is set the 10 Watt HouLight UV Black Light Flood Lamp on a flat surface with the light lens facing straight up.
For point of reference, the thorium-darkened glass is generally in the rear element group and exposure through that end might be even quicker.


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12-13-2019, 02:45 PM   #17
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QuoteOriginally posted by stevebrot Quote
For point of reference, the thorium-darkened glass is generally in the rear element group and exposure through that end might be even quicker.


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I did the first Super Takumar 50/1.4 base down first. It cleared about seventy percent but there was a dark area in the center. Doing it face down for another 10 hours cleared that up. The second lens I started face down, then went rear down. Same results and amount of time. So I think it’s a maybe/maybe not proposition.
12-13-2019, 02:59 PM   #18
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I went the free route and set my SMC Takumar 50/1.4 in a window that receives direct sunlight for several hours per day. Over the course of 2 months all of the yellowing disappeared.
12-13-2019, 03:04 PM   #19
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QuoteOriginally posted by steamloco76 Quote
I did the first Super Takumar 50/1.4 base down first. It cleared about seventy percent but there was a dark area in the center. Doing it face down for another 10 hours cleared that up. The second lens I started face down, then went rear down. Same results and amount of time. So I think itís a maybe/maybe not proposition.
Thanks...that is good to know. I have not used a UV lamp, just the IKEA desk lamp.


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12-13-2019, 03:26 PM   #20
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QuoteOriginally posted by Apet-Sure Quote
Wearing UV blocking sunglasses might be a prudent precaution if working around this light for any amount of time, though normally you would turn it on and walk away. Avoid cataracts later in life.
Even the deep blue is hazardous and can result in issues with the retina in later life (or after overexposure) so strongly yellow tinted glasses are a must when working with these types of light sources. A proper yellow tint will block all UV and blue wavelengths.
12-13-2019, 05:25 PM   #21
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QuoteOriginally posted by Bob 256 Quote
Even the deep blue is hazardous and can result in issues with the retina in later life (or after overexposure) so strongly yellow tinted glasses are a must when working with these types of light sources. A proper yellow tint will block all UV and blue wavelengths.
The idea behind using the particular light I did was to make setup quick and pretty foolproof while limiting heat exposure to the lens. There should be no reason for anyone to look at or be exposed to the direct UV light for more than a couple of minutes with any direct view being just a few seconds. Now, if you want to sit there and watch the glow, definitely wear the proper ANSI rated safety glasses.

Any easy way to keep all the UV away, cover the setup with a large cardboard box. Light canít get out and there is still enough air volume so the light probably wouldnít overheat.
12-14-2019, 09:02 AM - 2 Likes   #22
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QuoteOriginally posted by steamloco76 Quote
The idea behind using the particular light I did was to make setup quick and pretty foolproof while limiting heat exposure to the lens. There should be no reason for anyone to look at or be exposed to the direct UV light for more than a couple of minutes with any direct view being just a few seconds. Now, if you want to sit there and watch the glow, definitely wear the proper ANSI rated safety glasses.

Any easy way to keep all the UV away, cover the setup with a large cardboard box. Light canít get out and there is still enough air volume so the light probably wouldnít overheat.
Understand you're doing the right thing (your precautions in place) and that incidental short exposures aren't going to blind anyone (the fixture you mention is in the long-wave UV range similar to a blacklight poster lamp), but there are always those out there who will "sit and watch the glow" so too many warning are never enough. Looking directly at that 10W source is another matter since it's imaged on your retina and you'd be surprised how intense it actually is. Since most of the light output isn't visible, staring at it can happen, so that warning is mostly for the few who like to "look at the glow"
12-16-2019, 01:59 PM   #23
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that looks cool.. may even work to expose cyanotypes

12-18-2019, 01:34 PM   #24
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QuoteOriginally posted by steamloco76 Quote
I know there are other threads regarding using UV light to remove the yellow/amber/brownish tint which many 1950's-1970's Thorium glass containing lens develop. I'm adding this one because I found a super easy to use UV blacklight flood lamp which operates at a cool enough temperature to allow the lens to sit right on the flood light glass! I've done two fairly severely yellowed Takumar 50mm F1.4 lenses and the results have been OUTSTANDING.

Lens #1 was a late 1960's vintage Super-Takumar 50mm f1.4 with splotchy dark yellow elements. After about ten hours on the lamp face down and another ten face up, the lens is as clear as the day it left Japan. Lens #2 was a Super-Multi-Coated Takumar 50mm f1.4 from around 1971. It was evenly yellowed. I did the same treatment to it with equally excellent results. Photos of its treatment and the lamp are attached.

The BEST part? The UV flood lamp is only $16.99 US on AMAZON. It is a 10 Watt output version. They also sell 20 Watt and higher versions, however those lights generate more heat and would require the lens to be moved away from the lamp to keep the lubricant from overheating.

All you have to do is set the 10 Watt HouLight UV Black Light Flood Lamp on a flat surface with the light lens facing straight up. Plug the light into a 3 prong 110-115V receptacle. Take your Thorium yellowed lens, open the aperture fully and set it face down, centered over the LEDs in the UV lamp. I put mine on a rubber collapsable lens hood to be sure the lens elects didn't contact the lamp glass. After 8-10 hours, turn the lens over so the rear element is now toward the UV lamp and let it go another 8-10 hours. Check the lens by looking at something white under good lighting. If there is no more yellow cast (coatings are a bit yellow, so allow for that) you are DONE. If there is still some yellow, give it more time on the lamp. Easy. The HouLight is rated for 5000 hours of use, so you can do your friends lenses Too.
I have looked into this before but this is one of the more detailed explanation and examples I have seen, thank you for the information. I just got an old Takumar with some fungus that I would like to kill off before it gets worse. I've just been exposing it to sunlight, but a more systematic way sounds better. Since I am getting more into these older lenses, it might be handy to have it around for yellowing too.
12-18-2019, 03:38 PM - 1 Like   #25
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QuoteOriginally posted by Snapppy Quote
I have looked into this before but this is one of the more detailed explanation and examples I have seen, thank you for the information. I just got an old Takumar with some fungus that I would like to kill off before it gets worse. I've just been exposing it to sunlight, but a more systematic way sounds better. Since I am getting more into these older lenses, it might be handy to have it around for yellowing too.
The HouLight I purchased is very well made for the $17 cost. Housing is metal, with cooling heat sink fins. The cord is a heavy three prong plug type. Itís also pretty small so storage isnít an issue. Another user has cured UV activated glue with theirs, which is why I figured it put out enough UV to remove the yellow.
12-20-2019, 08:32 PM - 1 Like   #26
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QuoteOriginally posted by jlstrawman Quote
I went the free route and set my SMC Takumar 50/1.4 in a window that receives direct sunlight for several hours per day. Over the course of 2 months all of the yellowing disappeared.
Being ignorant, not aware of the issues of elements coming unglued, I put my 35mm lens on our patio { it was summertime} and the color cleared up within a few days without damaging the lens.
12-21-2019, 05:25 PM - 1 Like   #27
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I received my light from Amazon earlier in the week:








and can also say that it works - I have a Super Takumar 35/2 that was quite yellowed (so much so, I did not care to use it), but after two days' of sitting on the HouLight, the lens is considerably brighter and less yellow...
12-26-2019, 04:29 PM   #28
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Very interesting and some good info - thanks.
12-26-2019, 10:19 PM   #29
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QuoteOriginally posted by gaweidert Quote
As long as the radioactivity is not impaired I am okay with using this method.
If radioactivity could be removed with an UV light, it would be a major discovery and a net solution for nuclear wastes.

Besides, as far as I know, lens maker used thorium for its high refractive index. The fact that Thorium is radioactive is an unfortunate side effect, and has no net value when it comes to lenses.
12-27-2019, 06:55 AM   #30
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QuoteOriginally posted by Bertrand3000 Quote
If radioactivity could be removed with an UV light, it would be a major discovery and a net solution for nuclear wastes.

Besides, as far as I know, lens maker used thorium for its high refractive index. The fact that Thorium is radioactive is an unfortunate side effect, and has no net value when it comes to lenses.
Thorium works great until it turns the lens yellow. There is a lot of glass out there that is radioactive and it is not just lenses. A friend of mine has a set of old hurricane lamps that are radioactive. Thorium was not just used in lenses.

Last edited by gaweidert; 12-27-2019 at 07:46 AM.
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