Double Trouble -or- Mellow Yellow

Double Trouble -or- Mellow Yellow

You may remember that I just got a nice copy of the 8 element version of Super-Takumar 50mm f/1.4, and I explained that there was a later version with 7 elements and other versions too- this excellent video details all the different ones…

Well, as you can see above I did a bit of shopping on eBay and got myself copies of both the 7 element and the later Super-Multi-Coated versions that just arrived over the last few days. Now, don’t get upset- they were both really cheap (as they are the less rare and supposedly worse performing siblings of the 8 element I got previously) so I grabbed them to see for myself what the differences are.

Now, one of the reasons they were so cheap is that both of these lenses are radioactive! (but don’t worry, not dangerously so). They used Thorium in the glass to supposedly improve the refractive index and performance, and one downside of this practice is that over time (and these lenses are around 50 years old) the thorium causes the lenses to turn yellow, which has happened to some extent both of the ones I bought.

This yellowing can be seen as giving pictures a nice, warm feeling, but with a modern camera with auto white-balance all that really happens is that you lose a stop or so of light, so I decided to try a nice trick I found… UV light, if powerful enough, can reverse the yellowing (due to science I don’t fully understand). Now you can either leave the lens out in the sun (tough at this time of year, and not really recommended as too much heat can melt the adhesives used in their construction), or you can get a UV lamp of the correct wavelength and use that. And as it turns out, after a bunch of research, I’ve found that a cheap LED desklamp from Ikea (this one) puts out the right wavelength in a nice, concentrated, cool way 🙂

So, here is one of the lenses in my office getting its spa treatment. I left it under the lamp for 24 hours (on a metal lid to reflect some of the light back) and then flipped it so the light was coming from the other end and left it for another 24, and this is the result:

I think it probably needs a little longer, but you can see definite improvement! In the pic at the top of this post one is untreated and one is partially-treated; once I have both of them as clear as I can get I’m really looking forward to doing a full comparison against the original 🙂

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