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01-15-2016, 02:48 PM   #16
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QuoteOriginally posted by npc Quote
Search around for the old discussion about the 8 element variant. I don't remember the details anymore, but the "typical" 8 element version lens body had a certain set of differences compared to the regular 7 element lens body. However, some people had copies that are 8 element - but the lens body was more like the 7 element version. I guess these are refered as "hybrid".

The rear element on this one looks like the the 8 element version, but the glass itself looks yellowed and as far as I remember the 8 element versions were not radioactive so I can't tell for sure.


I have both lenses the 8 element and the 7 element. The 7 element is one of the earliest versions of this lens before it went SMC. It is also radioactive. Functionally it is very hard to tell the lenses apart. I thought I had an 8 element when I first purchased it and the seller also listed it as an 8, until I did a little bit more research. Still it is a very good lens almost cinematic in its rendering, that's why I kept it...

01-22-2016, 06:20 PM   #17
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So, the lens arrived today and I started deyellowing proces with two UV currency checker lamps. I have removed the rear elements and left them exposing to UV.
In the meantime I am going to go to a physics institute in my city and let them measure the radioactivity first hand, I have recently cotacted them via e-mail and the guy from atomic department said that I am at no risk even if I ate the lens. But if I want to, I can come over and they will test the rate and energy of radioactivity for me. Since I am curious about nuclear physics ayway, I will arrange a meeting.


I will post the deyellowing results later. I made "control" images of white background with my sigma 17-50 at f5.6 at 50mm, and I have to bring up exposure for about +0.85 on ST to match the exposure of Sigma. WB is off about -2100K from 5300.
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01-26-2016, 01:17 PM   #18
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So, after 4 straight days of deyellowing this is the result. I added a small multiple LED UV torch on top of the element just to boost the process. It is much much better now and it has been like this since day 2 but it is still a bit yellow, a tiny ammount which I can't get rid of. Do I need a more powerful setup or is this it, maximum deyellowing it can be achieved?
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01-26-2016, 01:45 PM   #19
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QuoteOriginally posted by zvon Quote
So, after 4 straight days of deyellowing this is the result. I added a small multiple LED UV torch on top of the element just to boost the process. It is much much better now and it has been like this since day 2 but it is still a bit yellow, a tiny ammount which I can't get rid of. Do I need a more powerful setup or is this it, maximum deyellowing it can be achieved?
Your "after" looks a lot like the best I was able to achieve with my ST 55/1.8 and Auto-Rikenon 55/1.4 using the famous IKEA JANSJÖ desk lamp.* You may be able to bleach it down further, though I suspect there are limits.


Steve


* Yes, the JANSJÖ does work. Why is up to speculation...

01-26-2016, 01:48 PM   #20
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I got gin-clear on mine using simple sunlight, but it took three weeks.
01-26-2016, 03:12 PM   #21
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QuoteOriginally posted by stevebrot Quote
Your "after" looks a lot like the best I was able to achieve with my ST 55/1.8 and Auto-Rikenon 55/1.4 using the famous IKEA JANSJÖ desk lamp.* You may be able to bleach it down further, though I suspect there are limits.


Steve


* Yes, the JANSJÖ does work. Why is up to speculation...

Maybe someone should make a spectrum analisys of that particular light. Usually cheap noname LEDs have a dirty spectrum, so possibly it emits some UV as well as visible light. Hell, maybe the deyellowing proces is not because of pure UV, maybe something else within those light sources is making the bleaching go faster, slower or making it happen at all.

Anyways..
I think that the problem I have is because I use UV neon tubes of money detectors, only small portion of the light goes through glass. But the light from LED torch which fits perfectly over the element is practicaly 100% shining through the element so I think that most of the bleaching came from that particualr torch rather than money detectors
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01-27-2016, 12:53 PM - 1 Like   #22
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QuoteOriginally posted by zvon Quote
Hell, maybe the deyellowing proces is not because of pure UV, maybe something else within those light sources is making the bleaching go faster, slower or making it happen at all.
I think you are probably on to something there. I did a little research on radiation-induced color in quartz and glass a few weeks ago and it may be that the heat or IR from the sun/lamp may be doing the actual work.

Google: "radiation glass color centers"


Steve
01-27-2016, 05:11 PM   #23
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QuoteOriginally posted by stevebrot Quote
I think you are probably on to something there. I did a little research on radiation-induced color in quartz and glass a few weeks ago and it may be that the heat or IR from the sun/lamp may be doing the actual work.

Google: "radiation glass color centers"


Steve



I will google that. Very interesting topic.

I have also thought about to try IR for deyellowing, I allready have a large IR bulb for some reason which I can try. But than again, internet is writing about how UV and UV alone is bleaching these lenses, and if you take a brief look at many LED spectrums of "warm white" or "cool white" LED lights (probably JANSJÖ is one of them), you can see that IR radiation from those LEDs is not great, I would say practically non existing. Also is the case with true UV portion of spectrum but the crossing between UV and B is much steeper than it is from IR-NIR and R.

This topic would definitely make a great and interesting obscure scientific paper, finding out why that IKEA light bleaches the lens and why is UV better for bleaching and if it is the UV that bleaches the lens. Sun is probably the best way to bleach the lens because of the broadest wavelenghts you can own but it is slow and dependant on weather, especially in this winter months.

Also, it would be cool to find out why the yellowing is happening at the first place (and I don't mean scientific by quoting other peoples posts from various other forums), some people say that the glue in the glass is just aging and UV bleaches it, some people say that the glass and/or glue is changing structure as it is reacting with radiation from thorium and other elements in thorium decay chain which are responsible for beta and gamma going through the rear element.

And a brief look at this thing : Radiation induced color centers in silica glasses of different OH content says that some glass does react with gamma, although I have no idea what this paper is really about, it just makes me think. Fact is that older the lens, the greater is the yellowing. My lens has a serial number 2066114 and was much more yellow than I saw on images of 3000000+ serial number lenses. And I found some paper saying that the older the thorium glass element is, more gamma and beta it emits, but that output gets stable over time, it doesn't go up forever. So if you have a brand new thorium glass element made in the factory, it would probably be outputing pure alpha radiation, and over time as many daughter decay element isotopes begin to appear in glass, some more stable than the other, which emit gamma and beta they could potentially induce the yellowing of the glass via those gamma decaying isotopes. Until someone makes a valid scientific research we can just keep bleaching the lens using sun, blacklights, JANSJÖ's, and UV LEDs. But I am very interested in the physics and chemistry behind that whole process, it just tickles my inner scientist to question that.


Last edited by zvon; 01-27-2016 at 06:18 PM.
01-27-2016, 07:30 PM   #24
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QuoteOriginally posted by zvon Quote
Also, it would be cool to find out why the yellowing is happening at the first place (and I don't mean scientific by quoting other peoples posts from various other forums), some people say that the glue in the glass is just aging and UV bleaches it, some people say that the glass and/or glue is changing structure as it is reacting with radiation from thorium and other elements in thorium decay chain which are responsible for beta and gamma going through the rear element.
I used to think it was glue, but there was work by a forum member a few years back showing that the non-glued elements were stained. Apparently activation of so-called "color centers" happens with when the radiation interacts with additives in the glass. The color depends on the additive. The same thing may happen with natural crystal (amethyst is a good example).

As for the radiation, you are correct in that it is the long-lived daughter isotopes that cause the gamma and beta emissions.


Steve
01-28-2016, 07:07 AM - 1 Like   #25
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QuoteOriginally posted by stevebrot Quote
I used to think it was glue, but there was work by a forum member a few years back showing that the non-glued elements were stained.
That could be me, and my experiences with radioactive lenses

To get more relevant hits, google on glass browning, i.s.o. yellowing.
01-28-2016, 10:28 AM   #26
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QuoteOriginally posted by glasbak Quote
That could be me, and my experiences with radioactive lenses

To get more relevant hits, google on glass browning, i.s.o. yellowing.

excellent, exactly the data I was looking for. Thank you very much for posting that
01-28-2016, 01:05 PM   #27
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QuoteOriginally posted by glasbak Quote
That could be me, and my experiences with radioactive lenses

To get more relevant hits, google on glass browning, i.s.o. yellowing.
Thanks for jumping in! I like your observation regarding the spotty occurrence of radioactivity in the 55/1.8. I have two of those lenses (ser. 832885 and 3637518) and only the newer lens had yellowing.


Steve
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