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03-13-2013, 05:55 PM   #1
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Yellow Takumar and UV Wavelength?

Hi
I have recently purchased a Super Takumar 50 1.4 which looks to be the 6 blade, 7 element version.
The lens does seem to have some yellowing, as is expected and reported for this lens.
I am aware that UV light is the answer to clear the yellowing, but have a question on that.

I have access to a UV lamp from a science lab, which can be set to either of two different wavelengths...Short Wave 254nm or Long Wave 365nm.

Does anyone have any thoughts or experience on which wavelength would be the most effective at clearing the lens?

Thanks in advance for any input.
Cheers
Dean

03-13-2013, 06:17 PM   #2
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Short Wave is more likely to clear it up (medical germicidal setting). Of course the plain old Sun with direct light is your best bet.
03-13-2013, 06:33 PM   #3
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You're in the UV capital of the world, but would you believe it, it's acutally cloudy and raining in Perth today. Having said that, the BOM is still saying UV index is 10 today.
03-13-2013, 07:27 PM   #4
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Thanks Docrmw and calsan.

As pointed out, rainy and overcast today...surprising in Perth at this time of year! Of course, it doesn't seem to make any difference to UV level...everyday of the year seems to be listed as "Extreme", right?

The lens is under the lamp today, I'll set it to Short Wave on your advice and see how we go...then back to the window sill I guess.

Cheers
Dean

03-13-2013, 07:37 PM   #5
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I would be careful about using the sun as the heat can cause the wonderful grease that makes Takumars smooth as silk to liquify, and then you've got all sorts of problems. The UV lamp is the best bet and I think the shorter wavelength should be more efficient. Though I've never tried to de-yellow my Tak, I've seen folks put a piece of aluminum foil over the front element, shiny side facing into the lens to maximize internal reflections during the procedure, then bombard it from the rear.
03-13-2013, 07:52 PM   #6
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Thanks maxfield_photo
Hmmm...good point on the temperature, black metal lens in hot Australian sun...I can see how that could be a problem too.
Well, I'll see if there is some improvement under the lamp with Short Wave today and decide where to from there.
I'll also post a quick update on how the process goes...though I haven't photo journaled before/after shots etc.
Cheers
Dean
03-13-2013, 08:11 PM   #7
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I cleared up one Takumar in the window in a week and a half. For the second one I wanted an option with less chance of something getting knocked on the floor so 8 hours under a stamp collector's black light bulb with a small fan set up to cool it did a much better job. I expect that your fancy scientific lamp will clear the lens up in hours .
03-13-2013, 08:38 PM   #8
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I was looking for answer for same question.
My suggestion is to try long wavelength UV, for two reasons: 1. short wavelength UV, e.g, UVC, can hardly arrive the surface of earth; the vast majority of UV reaches us is UVA and UVB, longer wavelength UV. Since sun light can clean it out, I believe UVA or/and UVB can do the job. 2. regular glass can absorb UVC very strongly, while longer wavelength UV can pass. So if you put the lens under (pure) UVC, the chances are: you kill all the germ outside and still see yellowing.
Good luck!

03-13-2013, 10:30 PM   #9
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Thanks for all the input.
My physics isn't great, so my thoughts are those of a layman...

grahame, what you have said makes a great deal of sense...however, the fact that a windowsill does not receive much (if any) UVC doesn't mean that UVC won't do the job, just that we know UVA and UVB will do the job. Perhaps the different absorption characteristic of UVC will make it more effective?

Steinback, I hope you're right and that the lens cleans up after a day!

Once I have a chance to inspect the lens this evening I'll post the result. Be interesting to see the result...yellow and germ free or nice clear lens. If no good I'll run it with the Long Wave tomorrow and see.

Cheers
Dean
03-14-2013, 12:47 AM   #10
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I expect little effect at 254nm, maybe more effect at 365.
I know that a blacklight (about 400nm) does work much better than a low pressure mercury lamp.
03-14-2013, 02:47 AM   #11
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Thanks glasbak.
So, day 1, looks a little better to my eye...but still a pretty noticeable yellow hue.
Back to the lab!
We'll hit it with the Long Wave for a day and see how that goes. On the plus side I'm sure it is "disease free".
Cheers everyone.
Dean
03-15-2013, 04:27 AM   #12
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Just a quick update.
After a day under the Long Wave it is very close to clear...I think the Long Wave is the ticket.
I did take a few around the house and yard shots after Day 1, to test the lens, and other than the yellow needing to be toned down the first impressions very good...looking forward to using this lens!
Cheers
Dean
04-09-2013, 07:19 PM   #13
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Sorry if this topic is already dead ^^;;

When I heard about the "cure" for yellowing lenses, I was curious if a UV lamp could be used instead, and thanks to Dean's experimenting, it does seem to be much more efficient than the sun.

Scientific-use UV lamps are usually high intensity and fairly accurate around a certain wavelength. I wonder if anyone has tried this with an everyday long wave UV lamp or flashlight (much cheaper).
04-09-2013, 10:02 PM   #14
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For what its worth. I cleared mine up by leaving the lens cap off and pointing it at the window when not in use.

It took a year (well it was a about a year later when i remembered about the de-yellowing and it was clear :P but I wasn't really worried to begin with :P
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