Which UV wavelength for de-yellowing rare earth glass lenses?

[coors]

Hi,
Can anyone share their experience concerning de-yellowing old lenses that use Lanthium, etc. rare earth glass and have yellowed from the low-radiactive emmisions, over time. I have one of the 50-LED, 385nm with Woods filter flashlights. Will this do anything useful or should I use sunlight or some other kind of UV light? Any help you can offer would be great!

 

[Aquanaut]

Lanthanum is dissolved within the glass to change its optical properties. The only thing I can recommend is to use a blue filter to attenuate the yellow transmission of the glass.

 

[Aquanaut]

I found a reference using UV to help remove the yellow:

http://www.rangefinderforum.com/forums/showthread.php?threadid=81759

 

[fyrstormer]

How strange. I wonder what sort of ionizing-radiation damage could be reversed using more ionizing radiation?

 

[coors]

Thanks, for the link! I have read this thread before. Was hoping to find an expert here at CPF that knows all about this issue and the remedy. I do have a bit of a problem with putting a $500+ lens in direct sunlight, even if it's covered in foil, as the lens elements themselves will heat up considerably, potentially causing the helical grease to breakdown, causing problems with the helical and possibly causing oil to migrate to the lens's iris mechanism. Am also concerned about both the heat and UV rays effect on the various cements/epoxies used for cementing the various element groups together...balsam in particular. I've considered buying a 254nm light (dangerous to all living organisms), but I'm not certain that this is the optimal wavelength for this kind of thing. Still searching.

 

[fyrstormer]

What about getting a filter that only allows UV light to pass through, and putting that on top of the lense assembly while it sits outside?

 

[coors]

Thanks, for the suggestion! That might work well. I have a "woods-filter" that is the lens of a 50 LED array, 385nm UV flashlight. I'd guess that it has about a 60mm diameter, so it might just work for me.

 

[coors]

Does anyone have any idea as to whether the compact fluorescent bulb, in the pic at the link provided by Aquanaut ( http://www.rangefinderforum.com/forums/showthread.php?threadid=81759 ), is visible spectrum or UV? I tend to think that it's even warm white, but how could 10 hrs of radiation from a warm white compact fluorescent bulb de-yellow a "hot" lens?