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Old 22-02-2009, 08:49 PM
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avandonk
avandonk

avandonk is offline
 
Join Date: Aug 2005
Location: Melbourne
Posts: 4,786
It depends on what is contaminating your optical surfaces. Isopropyl Alcohol is great for only one good reason, it's rate of evaporation is such that there is no condensation of nasties from the atmosphere as is produced by ethyl or methyl. The rate of the evaporating isopropyl is such that it's evaporating cloud shields the surface from condensation due to evaporative cooling.

To remove non polar nasties analytical quality petroleum ether is good. A very dilute non ionic detergent such as Teepol is also good. These should be very gently cycled until all residue is removed.

The anti reflection coatings on your optics are porous at a molecular level to the contaminants that really take hold. Only the best methods of coating can minimise this porousity. RF ion bombardment coating helps.

Unless you know what you are doing do not do it. Get advice.

Sometimes even a tiny bit of caustic in a cleaning solution is better than repeated attempts that cause physical (abrasive) damage to the AR coatings. The AR coating is unaffected by weak caustic solutions. It is the bond between the glass and the AR coating that is damaged as any caustic solution will dissolve glass at the molecular level at the glass AR coating surface interface! This of course will vary by how much Sodium is in the glass. Yes sodium silicate is soluble in even a mild caustic solution. Remember those 'tree gardens'.

After all that, I bet Mike is glad he has already done it! He used a tried and true method.

I have found one of the stickyest contaminants is a vapour or micro drops? That comes from gum trees.

I have had all sorts of contaminants on my 300mm lens including a very big deposit left by a magpie just after dawn. There is no point having good optics if you dont use them. The cunning design of the canon 300mm lens is that the front element is a flat and is 'relatively' cheap to replace. It does the same job as a UV filter.

Sorry for the rave. I have had too many cough medicines .

Bert
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