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250mm lens repair article
With the iris assembly still out it gave a good opportunity to clean
the old lubricant residues and dust particles off the rear lens element.
This proved to be the most difficult operation of the whole job as lens
cleaning fluids just caused smears and smudges.
I believe that there was a very thin coating of oil covering the whole
glass area which contaminated the clearing fluid every time it was
applied causing it not to evaporate properly.
So each time I put the cleaner on it it just got worse and worse. -
Bummer...
In the end a bottle of Vodka was the answer !
No , I didn't drink it .... I used it for cleaning.
Gently applied with a large cotton face wipe it cut through the mess on
the glass quite well and after 2 or 3 applications the glass was
perfectly clear once again.
In fact , it is surprisingly clear !!
The Vodka cuts through grease so well I used it all over the lens body
as well , see how clean the detent grooves are with only one wipe.
The Vodka was 60% alcohol and the rest is mostly water (how can people
drink this stuff ?!?!) so it should be fairly mild and not damage
lens coatings , but saying that I would not soak a lens in it for any
length of time.
Perfect for metal parts , but caution is advised around lens
glass areas.
Iris body now re-fitted back into the main lens body.
This is the middle element and man its huge !
Surely it must weigh 800 grams by itself and it contributes to much of
the assembled lenses weight.
Sadly the designers didn't make a nice focus mechanism that works well
having so much weight hanging off the front , so the Arsat 250mm is a
little stiff to focus unless the front of the lens is supported.
Unlike the rear element this one cleaned up VERY easily with normal
fluids , and again , it is now amazingly clear.
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