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11-15-2012, 12:26 AM   #16
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I have a 105mm f2.4 for Pentax 6x7 that exhibits yellowing. Right now I've had it under a UVA reptile light for 3 days, but it is still noticeably yellow. The serial is 4241097.

Do i need a better UV light? Or is my lens coated with something?

11-15-2012, 11:59 AM   #17
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QuoteOriginally posted by Mgarber Quote
I have a 105mm f2.4 for Pentax 6x7 that exhibits yellowing. Right now I've had it under a UVA reptile light for 3 days, but it is still noticeably yellow. The serial is 4241097.

Do i need a better UV light? Or is my lens coated with something?
Do you know which element is causing the yellowing? Maybe you can target that element. If it's at the rear, put the UV light at the back.

I tried this with another lens, taking it apart and putting each element in sunlight, but in a window that was probably UV coated. I gave up after the dog managed to knock everything onto the floor.
11-15-2012, 06:06 PM   #18
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QuoteOriginally posted by Just1MoreDave Quote
Do you know which element is causing the yellowing? Maybe you can target that element. If it's at the rear, put the UV light at the back.
As far as I can tell, the tint appears to be concentrated in the back element. The front of the lens says Super-Takumar / 6x7
11-15-2012, 06:12 PM   #19
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Jam the light as close as you can to the glass. Put tin foil underneath so it reflects back up from the bottom. Flip it over every day so you work both sides. You should see difference after a few days, but not necessarily perfect. Some of them never become totally clear -- that may just be a property of the glass. I have never been able to get any Super-Tak to look as neutrally clear white as a later SMC-M lens for instance no matter how much treatment, but they all end up the same as each other (the super-taks) so I guess that is just the way they are. And some other lenses are noticeably cool looking through.

11-15-2012, 06:24 PM   #20
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QuoteOriginally posted by vonBaloney Quote
I have never been able to get any Super-Tak to look as neutrally clear white as a later SMC-M lens
I have a later SMC Pentax 67 1:4 45mm that I can compare to. It is definitely on the cool, or clear side. I'll look for a fluorescent black light, that might work better.
11-15-2012, 06:29 PM   #21
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QuoteOriginally posted by Mgarber Quote
I have a later SMC Pentax 67 1:4 45mm that I can compare to. It is definitely on the cool, or clear side. I'll look for a fluorescent black light, that might work better.
LED lights actually work pretty good.
11-16-2012, 10:29 AM   #22
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Big news! I wasn't losing light due to yellowing, although some is present. I've discovered that my shutter is slightly too fast. I did extensive tests, and made an animation to time the shutter. The results can be seen here (using my 5D as control) more MSG!

The Pentax 6x7 shutter is slightly too fast. Now, the question is how to fix it.
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