Please Tell Me What's on my Lens...

[Richard K.]

I bought a Euryscop about a month ago and it has this wispy, smokey green-black discoloration in between the 2 rear elements and a little on the front too. It looks almost metallic upon reflection (its, not mine!) Is this fungus, separation, botulism, pestilence :eek: , oil slick or what? Will it worsen? Appreciate your insight! Thank you...


http://i300.photobucket.com/albums/nn15/RichardK47/Lens1-1.jpg

http://i300.photobucket.com/albums/nn15/RichardK47/Lens2.jpg

[John Schneider]

I have something similar on a Protar V 8" C-set cell. Looking at it under a low-power inspection microscope didn't tell me anything, other than it isn't fungus. Just to make sure I zapped it with shortwave UV for several days, with no change. I suspect it's a deterioration of the balsam, but why it turns this color is beyond me.

[Steven Tribe]

Having done about 10 balsam jobs now - mostly on RR's like yours, I would humbly suggest this is balsam breakdown. The green colour is always present in canada balsam and this can become more apparent when the layer is disturbed. The metallic sheen is due to the Newton ring effect - like oil on water. The balsam migrates onto the edge of the lenses and even further.

[Richard K.]

Thank you John and Steven. Will this progress further, do you think?

[Steven Tribe]

Not unless you live another 100 or so years! If it is optically usable now - then it will OK for a long time. Some of my re-balsam activities are more aesthetic more than optical demands.