0
Я, с вашего позволения, сначала приведу оригинальные письма, а потом попытаюсь перевести. Не уверен в достоверности перевода
Saturday, February 4, 2006 lmd91343 wrote:
I am so happy!
I just removed my FD BL 35mm f2 concave chrome nose and SMC Tak 50mm
f1.4 from my window sill. They are both WATER CLEAR!
I put them in my south facing single pane window in May and removed them today! Hooray! Hooray!
They both had thorium tints making them look like tea.
I wrapped them in aluminum foil, covering the front element on my Tak and the back element on the Canon. The thorium doped element is near the back on the Tak and near the front on the Canon. I tilted them at a 30* angle due south. Tak bottom up, Canon top up.
The aluminum foil kept the lenses cool, reflecting all light except what came in through the exposed element. The light was then reflected on the inside of the covered end back through the affected element. Each photon made a double pass. The helical lubricant did not melt. The diaphragms are oil free and snappy. I checked the temp of the lenses several times a day the first month in the window, and again when the weather turned hot. They never got warm to the touch.
I now have rehabilitated the sharpest lens from each line! I guess I can retire my FDn 35/2.0 now!
Hooray! Hooray!
-Lance
P.S. I had two failed bleaching attempts
1) 24/7 UV light placed over lens with fan to remove the heat for one month - no change
2) same window for 3 months with 98% shade cloth over window - no change DUH!
Monday, February 6, 2006 Sergey Ilyin wrote:
Sorry, it looks like you describe 'well known method' but I am a novice here. Can you briefly say -- what is the idea?
You put this lenses to the bright sunlight for weeks? monthes? years? and the "yellow lenses" became clear?
And, if so -- where do you live? How bright is your "bright sunlight"?
Monday, February 6, 2006 lmd91343 wrote:
Sergey,
Thorium doped elements are radioactive. As the small amount of thorium sand, mixed in the glass matrix degrades to its eventual daughter products, the glass turns brown. Over time the element will get darker and darker. Some of the Kodak Ektar lenses from 60 years ago are very brown. Our 35/2 lenses will suffer the same fate.
The brown color can be "bleached" by exposing the affected element to UV radiation. This does not reset the thorium and its daughter products back to their original composition. A bleached lens will start to turn brown again at the same rate as before the bleaching. Every 10 years the lens will need to be bleached to keep it water clear.
The easy and cheap way to bleach the lens is to expose it to sunlight. I wrap the lens in aluminum foil to keep it cool by reflecting all of the sunlight. The back element of the lens is also covered with the foil. Only the front element is exposed. It
looks as if the lens was set in a silver cup. I then placed the lens in my south facing window, tilted to match the angle of the sun. Wait three months and VOILA!
I am sure that I could have pulled the lens from the window earlier. I put the lenses there and forgot about them!
I read of a fellow who moved his lens from window to window around his house all day and bleached his lens in two weeks!
The first few days, I constantly checked the temperature of the lenses. I was afraid of them getting too hot and the lubricant melting and oiling the blades. The lenses only warmed slightly over room temperature.
I live in Los Angeles, CA, 33* north. My house A/C is set for 80*. I have single pane windows.
-Lance
Вот. Насколько я понял -- оборачиваем корпус объектива фольгой, чтобы он не перегрелся и не потекло масло. После чего три месяца облучаем "желтый" элемент солнечным ультрафиолетом.
Но -- товарищ живет в Калифорнии. У него с ультрафиолетом нет проблем.
