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Old April 1st, 2007, 11:36 PM   #1
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Lenses Gone Yellow/brown

I recently finally got hold of a Nikkor f1.4 35mm and with reluctance sourced it from ebay. Ebay did not rob me blind, sell my identity to the entire universe and the entire transaction, despite my paranoia turned out just fine.

From the pics I knew the lens would have some discolouration and it did. For video it is not a big issue because manual white-balance takes care of it. We all meticulously white-balance across all lens changes don't we???

The problem with discolouration is that it removes light and lowers the performance of the lens.

There are evidently two causes for a changing warmish discolouration in older lenses.

One is breakdown of the bond between cemented elements. In older lenses this bonding material was known as Canada Balsam. It is basically tree gum and has served the optical industry very well. This I can deal with if I have to.

Another is a discolouration of optical glass due to radioactivity. Earlier fornulations of low dispersion glasses contain thorium which is essentially the nuclear reactor that couldn't or once would have been. This glass turns brown over time.

In stages of its breakdown over multimillenia, thorium emits radiation. Apparently, a year's constant human exposure to the lens would sum up to one transatlantic jet flight's worth. Best practice would be not to shove the caseful of old lenses under the bed you sleep on at night.

Ramble over - also posted on the internet where I read this stuff, was a suggested solution to restore discoloured lenses containing thorium glass. Apparently, it is as simple as exposing the glass to about a week's worth of strong sunlight.

When doing this. the recommendation is to wrap the lens barrel in cooking foil. I guess this is to reduce heating of the metal and maybe some stresses being set up.

So for the next week, the discoloured Auto-Tamron and Nikon have gone up on the roof wrapped in alfoil inside a clear oven bag to keep the dust and rain out.

I shall advise how it works out.

Last edited by Bob Hart; April 1st, 2007 at 11:39 PM. Reason: errors
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Old April 2nd, 2007, 12:40 AM   #2
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Bob, very interesting. Any idea how the sunlight works it's magic? I'm assuming UV light?

I didn't know that about radioactive lenses. I'm going to start making my millions with a patented follow focus made of lead.
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Old April 2nd, 2007, 01:11 AM   #3
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Interesting indeed Bob!


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Originally Posted by Ben Winter View Post
I'm going to start making my millions with a patented follow focus made of lead.
RoHS compliant I hope...


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Old April 2nd, 2007, 03:02 AM   #4
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I don't get it. People spend thosands of dollars on their camera and adapter setups with lens support, rails, external monitors, storage, and whatnot and then go and buy a 50 dollar POS lens from ebay that's irradiated with more gamma rays than the Incredible Hulk. Thanks for the tip, Charles.
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Old April 2nd, 2007, 08:39 AM   #5
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I don't get it. People spend thosands of dollars on their camera and adapter setups with lens support, rails, external monitors, storage, and whatnot and then go and buy a 50 dollar POS lens from ebay that's irradiated with more gamma rays than the Incredible Hulk. Thanks for the tip, Charles.
It's true, that has upset me as well. But the fact is we're all penny pinchers, and it's just not cost-effective to buy several hundred dollar lenses when the adapter+camera only resolves about a fourth of the lines of resolution a good lens is capable of anyway.
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Old April 2nd, 2007, 04:53 PM   #6
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put lenses on the roof so the sun's UV can break down the radiation?

april fool's was yesterday ;)
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Old April 2nd, 2007, 05:41 PM   #7
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The UV light apparently does something to the stain already created by the radioactivity. The radioactivity remains for the lifetime of the thorium which is longer than the lens, our civilization and indeed our species will. The article also suggested several artificial UV sources.

It may all be unmitigated passings of the bull, however the article was written by someone who knows his physics and astronomy and the article was found via a link from a discussion forum. One week up on the roof or several under a high intensity UV lamp will see the truth of the matter.

At worst the cemented doublets will separate or the magpies will peck holes in the over bag and let the rain in. Otherwise, it will cost me absolutely nothing. the roof is chose because leaving on the windowsill at groundlevel means tree shade and possible theft.

The lens is a bit more than the suggested $50. It seems too may adaptor builders and Mini35 owners are inflating the market for the f1.4 stuff.

Last edited by Bob Hart; April 2nd, 2007 at 05:46 PM. Reason: spell error.
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Old April 5th, 2007, 05:25 AM   #8
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The lenses came down off the roof today because it has been trying to rain. There's been overcast for part days over last three days and only about one day's worth of sunlight. There does not seem to have been any effect so far but it is not a fair test.

Will try again when better weather comes along.
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Old April 5th, 2007, 09:49 AM   #9
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Bob,
I'm wondering if the plastic covering you're using might block UV light.
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Old April 5th, 2007, 11:29 AM   #10
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Ben.

That same thought crossed my own mind.

Once the sun comes out again, I may smother the lenses with sealastic to seal out any rain or moisture and put them up on the roof again in their naked glory.

There seemed to have been some effect on the Tamron. I had it facing the light. On the Nikon f1.4 35mm the widest optic is at the back of the lens so I aimed this at the sun. The offending element might be at the other end.

Apparently the other non-thorium elements can also filter out some UV along with the thickness of the discloured element itself at centre.

If I could put them in the lamphouse of old carbon-arc projectors I once operated it would be fixed in a heartbeat. Trouble is, they are now 1500km away and may well have been pensioned off by now in favour of cold lamps.

I would have liked to have got a newer lens but I have been getting outbid - too many people wanting 35mm f1.4

At worst, white balance should help but all the others are clear and it is a chore often forgotten.

Last edited by Bob Hart; April 5th, 2007 at 11:32 AM. Reason: forgot something
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Old April 6th, 2007, 11:46 AM   #11
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I stuck the 35mm on front of the adaptor today and for the same whitebalance, the image seems a little cooler. The blue sky colour seems natural.

This is hardly scientific as the lighting conditions nearly two weeks removed from my last setting of the whitebalance could be responsible. But it seems something might be going on after all.

Something I noticed again though the lens today. Climate change is beginning to bite despite that barrier of denial, business and some politicians have been putting up. There is a tree kill going on in the valley the likes I have never seen here before.

People with no linkage to the land simply haven't got a clue.
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Old April 6th, 2007, 11:42 PM   #12
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I got a really inexpensive AI 35mm f1.4 in mint condition about a year ago. It's a huge lens; considerably bigger even than the 28mm 2.0. Perfectly clear glass, too.

And it SUCKS at f1.4. Worse than the old ones, even: no contrast, blurry, vignetting like crazy. At f2.0 it's fine, though. 35mm is just about my favorite focal length, but it seems these lenses all have problems.

The 28mm f2.0 is amazing, though, except for the wonky bokeh toward the edges.
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Old April 7th, 2007, 10:44 AM   #13
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Lenses and sunlight

When I was working as a stills photographer, our lead assist used to cure internal fungus and discoloration by exactly the method described. We had quite a bit of that kind of lens problem, since we were in Hong Kong (high humidity, high spore count) and other points east.

Half a day in the sunlight, lenses not covered with anything, repeat the dosage if problem not solved. But usually it only took one or two times to cure all the lenses we had. (Mainly Nikons and Leitz lenses, three photographers, around 12 lenses apiece).

Still have a couple of those old lenses around (mainly only the high speeds), use them on my digital Nikons (actually Kodak DCSs, but I still have my battered old F3HP just in case) and, of course, on the 35mm system for my camcorder. And, more than 25 years later, I'll still sun them if they need it.
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