Re: ATM Cleaning eyepiece

["Andrew Schott" <aschott@digital.net>]

Damaged coatings and blotches are always a disappointment when dealing with
antique optics.  Cleaning/restoring can be difficult if not impossible.  I
don't have much experience with telescope eyepieces yet, most of my stuff is
still pretty new, but I have had my share of headaches with camera optics
and their degradation in the humid environment of Florida.

Without knowing the exact composition of the coatings or the lenses the only
safe thorough cleaning method is to take the lens assembly apart and wash
each element in soapy water.  The soap must be free of ammonia or alcohol.
You should avoid antibacterial hand soaps and dishwashing liquids as they
contain disinfectants derived from various solvents and lotions that can
etch, damage or remove coatings while leaving stubborn residue.  I've always
used a commercial brand of concentrated detergent available from Fisher
Scientific but there may be substitutes around in the supermarket world.
It's hard to find anything "off-the-shelf" that doesn't have Aloe or perfume
or lanolin in it anymore.  Check in auto parts shops or pharmacies for
unadulterated detergents.

My fundamental technique involves first removing the lens, rinsing it under
running water to wash off any major abrasive particles then applying several
sprays of the soap to both sides of the lens and using wet fingertips to
swab the soap around.  I hold the lens by it's edges with one hand and pinch
the surface between the thumb and fingers of the other and using random
circular motions - and quite a bit of pressure - I work the soap into the
entire surface.  Nothing can beat the human fingertip for it's qualities of
being able to debond oils and organic film,  maintain surface contact and to
scour away tough deposits while leaving the delicate surface intact.
Everything must be kept sloppy wet and slimy with soap while the surface is
worked over with the fingertip pads or else your own skin oils will bond to
the glass.  Do not allow the soap to dry on the lens even a little bit as
this will make a very hard to clean streak in the coating.  It helps to use
warm water but it isn't required.  Once the surface has been thoroughly
massaged and you can't feel any sticky or rough spots anymore, rinse.  Rinse
your hands and the lens by allowing water to cascade over the surface
without touching it.  Alternate hands so you can be sure to get all the soap
off your skin while holding the lens in the stream.  Pure detergent will
leave the lens immediately and the water will "bead" up in large drops as
the lens is now clean and will no longer wet.  Water won't stick to clean
glass so if it jumps up into big beads when you rinse you'll know you got it
clean the first time.  Dry your hands somewhat and grab a lint free wipe
like a Kimwipe or one of the more contaminant free paper towels.  Slowly
wipe the lens from one edge to the other allowing the towel time to absorb
the water without streaking.  Do not polish or buff as this only tends to
smear any remaining contaminants around.  If anything does streak or show up
as a smear it means you need to repeat the washing process.  If this fails
to remove the streaks, you may need to resort to other means of cleaning.
Acetone on cotton swabs is about as far as I go attempting to remove stuff
stuck on the lens.

Blisters, chips and mottling of the coatings is something that won't be
repaired by cleaning.  Typically, these defects won't occlude transmitted
images but will usually effect image contrast.  Lenses that have grown
opaque from contaminated coatings are usually beyond economical repair as
stripping and recoating would be costly.  Especially if the original type of
coating process was unknown.  I've tried stripping the coatings myself and
using the lens uncoated but the resultant loss of contrast and interelement
reflections caused as much problems as the ruined coatings.

----- Original Message -----
From: "Malcolm Macdonald" <toliman@wave.co.nz>
To: <atm@shore.net>
Sent: Wednesday, April 04, 2001 6:27 AM
Subject: ATM Cleaning eyepiece


>
>
>
> I resurrected a little 4.5" catadioptic scope that has been in the shed
for
> years, to see the sun spots. Unfortunately there were more spots on the
> eyepiece than on the sun.
<poit>