[Dangermouse]

The small Ikea LED desk lights do work. They also have other uses, unlike a plain UV bulb (unless you have fish or reptiles). I've heard of people using them for macro photography as they produce a crisp white light and won't pose a fire risk if you drape a tissue over them as a diffusor.

I left mine on for about a week, with an old CD underneath to reflect the light back into the lens. It's not absolutely perfect but it's a lot less yellow than it was.

[vonBaloney]

The small Ikea LED desk lights do work. They also have other uses, unlike a plain UV bulb (unless you have fish or reptiles). I've heard of people using them for macro photography as they produce a crisp white light and won't pose a fire risk if you drape a tissue over them as a diffusor.

I left mine on for about a week, with an old CD underneath to reflect the light back into the lens. It's not absolutely perfect but it's a lot less yellow than it was.

Some of the lenses have a natural warm tone (it seems) that will never go away, at least with a UV treatment. Others become cool. (Looking through the glass I mean, not image tint.) Sharpness is noticeably improved when you de-yellow a heavily yellowed lens -- definitely worth doing.

[Dangermouse]

The best comment I've seen on the Takumar glow was along the following lines:

"We don't mind so much when Aunty Flo has a warm glow in family portraits. We'd complain if she was blue or green!"

I've tried it since the treatment, the remaining yellow tone seems have negligable impact on the images.

[RockvilleBob]

You could also create a camera profile with a Macbeth Color chart.

[monochrome]

The atomic structure of the lens glass is altered by radiation from trace amounts of radioactive thorium in one rare-earth glass element, creating the yellowish-brown color; and this change is reversed by exposure to ultraviolet light.

Huh. I thought I read the Canadian Balsam glue between the rear couplet is what changes color (which is why you expose the rear to the UV light).

FWIW, I used the windowsill method to clear a yellowed S-M-C Tak 50/1.4. It took about 2 weeks and the lens is absolutely gin clear now.

[csa]

Great information posted here. I find the title very misleading: "Removing yellow tint from Pentax lenses".

Should be titled "Removing yellow tint from Takumar lenses"!!

Of course since I don't have any Tak's, I wouldn't have read this thread, if the title hadn't been misleading, I was wondering which Pentax's had the yellow tint!

[pathdoc]

Given that they and their immediate successors are all made by Asahi Optical Co, they are honorary Pentax lenses.