Pentax lenses, Thorium problem?

radiocemetery said:
Pretty spiffy set up John. What temp (K) is the compact flourescent that you used? I have a 50 1.4 that would benefit from this treatment, it is noticeably yellowish brown when looking through the lens against a white background. BTW I have two 50 1.8's that do not show this yellowing. They are Auto-Takumars and the 50 1.4 is a Super Takumar. Happy New Year.

Steve
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I don't know the Kelvin, but they are Chinese BLBs. I decided to try this after the hassle of sunlight. I have one more to go. I hope it is as quick as this one.
 
I didn't know compact black light flourescents were available. I will have to look around. I like your approach not only for the speed, but for the fact that there wouldn't be as much heating of the lens itself compared to parking it in a sunny window. Thanks.
 
radiocemetery - actually, the lens doesn't get "hot." Wrapped in foil, shiny side out, the black is protected from direct sunlight.
 
I have a Super-Takumar 50mm 1.4 lens coming sometime (hopefully) early next week...
I want to test it first before deciding if I want to clear it...
I work in the Printing Industry and some presses use UV Lamps to cure the inks and special clear coating used for glossy printing...These lamps produce close to 100% pure UV light...I'm guessing it shouldn't take too long to clear using the light from these lamps...
I can't place the lens where it will get direct light from the lamps but it can get light that leaks out through the openings in the Lamp Unit...plus leaving it in one of these units will just set the lens on fire...:D:cool::eek:
 
Yes, some people reported success with UV lamps after a few hours; the hardware-store type though
But since you are in CA, it should not take long to get the lens cleared out... it took me 2 weeks in the NC sun



nikon_sam said:
I have a Super-Takumar 50mm 1.4 lens coming sometime (hopefully) early next week...
I want to test it first before deciding if I want to clear it...
I work in the Printing Industry and some presses use UV Lamps to cure the inks and special clear coating used for glossy printing...These lamps produce close to 100% pure UV light...I'm guessing it shouldn't take too long to clear using the light from these lamps...
I can't place the lens where it will get direct light from the lamps but it can get light that leaks out through the openings in the Lamp Unit...plus leaving it in one of these units will just set the lens on fire...:D:cool::eek:
Click to expand...
 
The Leica lens I looked at had a yellow /brownish color. It seems not to effect sharpness but will color cast color film. Shame it was a absolutely mint coll Summicron in screw mount.

Lots of people tout the UV light cure so it must work at least temporarily. The problem with the cure is it takes too long and if unsucessful, the warrantee is gone. Maybe you can get a extension for the problem alone.
 
Sam - when your lens arrives, put a white sheet of paper next a window in daylight, hold the lens in your hand pointed at the paper and look through it. You'll be able to tell straightaway whether or not it has an amber tint. My Super Takumar 50/1.4 was seriously tinted, but as at that time I was shooting only black and white it didn't matter (doesn't affect lens sharpness). Later, when I decided to shoot color, I simply put it outside on a table, propped at a 45 degree angle, screw-mount end facing the sun and wrapped in foil with just the rear lens element uncovered. Note: remove front lens cap before wrapping in foil.

Clearing the tint took about 10 days.
 
or try 82A filter..

or try 82A filter..

I've got a similarly amber tinted Minolta MC W-Rokkor X SI 28mm / 2.5 lens and have found that an 82A filter restores proper color balance.... for those who need a quicker fix and/or may not want to leave the lens outdoors etc. for several days..
 
nikon_sam said:
I work in the Printing Industry and some presses use UV Lamps to cure the inks and special clear coating used for glossy printing...These lamps produce close to 100% pure UV light...I'm guessing it shouldn't take too long to clear using the light from these lamps...
I can't place the lens where it will get direct light from the lamps but it can get light that leaks out through the openings in the Lamp Unit...plus leaving it in one of these units will just set the lens on fire...:D:cool::eek:
Click to expand...

NO NO NO!

I work in the printing industry too. The UV curing unit in the presses emits UVB light, which can cause direct DNA damage (Cancer) if handled incorrectly. Whatever you do don't mess with the UV lamps in the presses.

Your best bet is to use the desktop curing test unit in your Ink Kitchen, this is the machine with the conveyer belt. However I expect you'll need quite a few pass to de-yellow your lens.
 
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