View Single Post
Old 19th January 2013
Zuiko's Avatar
Zuiko Zuiko is offline
Join Date: Nov 2007
Location: Dunmow, Essex
Posts: 22,052
Thanks: 1,981
Thanked 3,146 Times in 2,455 Posts
Likes: 3,380
Liked 4,453 Times in 2,114 Posts
Re: Fungus in cemented lens groups

Originally Posted by donmcmahan View Post
this is a very stale thread, don't know if there is any point weighing in at this late date but here goes. are you sure it is fungus? more likely it is the cement breaking down. I was an optical instrument repairman in the US Navy for 20 years. I have personally re-cemented hundreds, perhaps thousands of lenses. If the cemented group is put together with thermo-setting plastic, forget it, if it is cemented with Canada Balsam it is easily done by someone who knows what they are doing and has the equipment. Don't ask me where you might find someone, I have the skills but not the equipment.
Thanks for that explaination, Don. I had a 250mm lens for a Kowa 66 with the cement breaking down in the front group, around the edges. At wider apertures it caused noticable softness, but that disappeared upon stopping down to f16 and beyond. In all the years I had it the problem didn't appear to get much worse, so it seems that degradation of the cement can be a slow process. Is there anything in particular (such as the way the lens is stored) that causes the cement to break down, or is it just a natural consequence of age?

"A hundredth of a second here, a hundredth of a second there even if you put them end to end, they still only add up to one, two, perhaps three seconds, snatched from eternity." ~ Robert Doisneau
Reply With Quote