Lewis,
You're probably thinking glass is glass, right, so clean it like you would a window pane. Wrong. Your everyday experience is based on borosilicate crown glass, which is quite tough stuff.
i hate to break the bad news, but here's why you don't mess with fluorite objectives. You can see why Bintel don't want to touch them, either. Be very careful with ED glass too - while it is more robust than fluorite, many of the following comments do also apply to it to some extent. This applies to both the ED refractors as well as ED EYEPIECES such as the Vixen LV, LVW and quite a few from other manufacturers. IN SHORT - resist the temptation to take these apart as you will do more harm than good.
Quote:
Originally Posted by LewisM
Between the 2 objectives, there is a foggy layer ... I tried water and a little Sunlight dishsoap,but not much better. Seems like a fine machine oil
|
That "foggy layer" is a fluorite lens that is now completely ruined thanks to the well-intentioned but uninformed efforts of a first person, and now yourself.
#1. Fluorite is hydroscopic. In its anhydrous crystalline form, clear. But it will adsorb water if you try to clean it with liquids containing water, and the surface turns cloudy. Basically you can't fix this.
#2. Fluorite has a high thermal coefficient of expansion, and is soft and brittle. If you use "air in a can" or worse, solvents that cool rapidly (acetone comes to mind) and cause sudden cooling you will probably cause two things to happen. Firstly the antireflection layer will lose adhesion as its coefficient of expansion is different, and weeks later it will start to peel off in small flakes.
The second consequence can be the formation of micro-cracks in the fluorite that will eventually propagate and become a visible crack.
#3. Fluorite is soft, very soft. Ordinary cleaning materials you may think are safe on glass will easily abrade it - not polish it - producing the grey cloudy surface you see now. This includes tissues and cloth.
#4. Since it is much softer than an antireflection coating, once a pinhole forms in the coating, the more you "clean" it the worse it gets as you are abrading the fluorite underneath into a pit that expands.
#5. In refractor objectives fluorite was often the second element on the assumption that the front element would be the only one exposed to the outside night air, and dew; the inner element would be protected safely inside the tube and lens cell. Sometimes the second element had 1 or more UNCOATED surface, so washing this is basically a catastrophe. Similarly with ED eyepieces, the ED elements are inside, not the eyelens or field lens. They aren't intended to be dismantled and washed.
This is also one of the reasons why ES eyepieces are nitrogen-purged and sealed - they are waterproof.
Basically you now have a paperweight.
Got any photos?
