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Forum: Pentax SLR Lens Discussion 01-28-2016, 10:28 AM  
What did I buy? super takumar 50mm 1.4
Posted By zvon
Replies: 26
Views: 3,486
excellent, exactly the data I was looking for. Thank you very much for posting that :)
Forum: Pentax SLR Lens Discussion 01-27-2016, 05:11 PM  
What did I buy? super takumar 50mm 1.4
Posted By zvon
Replies: 26
Views: 3,486
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.
Forum: Pentax SLR Lens Discussion 01-26-2016, 03:12 PM  
What did I buy? super takumar 50mm 1.4
Posted By zvon
Replies: 26
Views: 3,486
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
Forum: Pentax SLR Lens Discussion 01-26-2016, 01:17 PM  
What did I buy? super takumar 50mm 1.4
Posted By zvon
Replies: 26
Views: 3,486
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?
Forum: Pentax SLR Lens Discussion 01-22-2016, 06:20 PM  
What did I buy? super takumar 50mm 1.4
Posted By zvon
Replies: 26
Views: 3,486
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.
Forum: Pentax SLR Lens Discussion 01-15-2016, 03:15 AM  
What did I buy? super takumar 50mm 1.4
Posted By zvon
Replies: 26
Views: 3,486
So basically 8 element is praised by collectors, but from IQ standpoind 7 and 8 are practically the same? Only minor optical differences that are astronomically unsignificant. And of course radioactivity and yellowing from thorium dioxide that can be cured with UV.



I am aware that people try to emphasize the items that they are selling, but this eBay listing has the nicest looking lens and others were a bit more expensive (when I count in the shipping) and a bit more worn. And if I won't like it or use it as much as I think, old lenses have been proven from my expirience to be some sort of neutral investment. Like I was just lending them from people, I always managed to sell them for the same price or a little bit higher than I originally bought them for. For example I owned above mentioned Pentax-A that I paid locally around $60 and two years later I sold the lens for $65, same thing happened with Tair 300s, bought it for $55 from a guy that was getting married and he sold me the entire metal box that was incomplete, Zenit was broken but Tair 300s and Helios 44m-4 were fine. About a year ago I sold the Tair for that same exact ammount. I have given Helios away to a friend because I allready have the first edition one.
Forum: Pentax SLR Lens Discussion 01-14-2016, 05:33 PM  
What did I buy? super takumar 50mm 1.4
Posted By zvon
Replies: 26
Views: 3,486
I understand. I guess, sort of. I haven't done much research because I didn't think it can get that complicated. I wanted a manual lens since I stupidly sold my Pentax-A 50mm 1.7 few years ago and I saw how great ST 50mm 1.4 can be. Usually when buying old manual lenses I like to buy ones that are not used much, those that were in someones uncle cabinet in the attic for years. And this listing shows the lens that are in that kind of condition. So why is this "hybrid" (call it that for sake of identification) or 7-element ST worse than 8-element?



So you have an 8-element with serial 2293854 and soon-to-be-mine 7-element has 2066114. How could they produce a 7-element with 2066114 and then later go back to 8-element? Or am I saying something that doesn't matter? I really don't know how to read these specific serial numbers.

---------- Post added 01-15-16 at 02:01 AM ----------

Sorry for that, I messed up. I thought that lens on the left is 8-element.
Forum: Pentax SLR Lens Discussion 01-14-2016, 04:21 PM  
What did I buy? super takumar 50mm 1.4
Posted By zvon
Replies: 26
Views: 3,486
I just bought this lens from ebay:

Asahi Pentax Super Takumar 50mm f/1.4 HYBRID Rarity Tested TOP condition M42! | eBay

It is noted that it is a hybrid and I have been searching for proof around the internet but I can't find the definite one.

So, can somebody tell me, do these 50mm 1.4 hybrid super takumars exist? Are they 7 or 8 elements? and are they radioactive? (not that I mind that, I can find somebody with a geiger counter and test it for myself)
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