Glass cleaning is a common topic among amateur astronomers. Big
pieces of _very_ expensive coated glass and mirrors.
The general consensus among both users and manufacturers is that
commercial glass cleaner is okay for oculars (eyepieces), but not
for objective lenses. BTW, the electronics people all say to NOT
use Windex because it is corrosive to many metals, but to use
Glass Plus instead.
For coated objective lenses (and mirrors) Isopropyl Alcohol 99%
for the initial cleaning, and then Acetone C.P. to finish.
Use _only_ 1000ure cotton ... Johnson & Johnson balls or surgical
pads are fine ... just be certain that they are 1000ure cotton.
Never use a lens brush because after a few uses they themselves
become contaminated. First use an air bulb (a drugstore ear bulb
is much less expensive that a camera store bulb) to blow away the
loose stuff. Don't use your breath or canned air ... to many
contaminates! Dampen a cotton ball or pad with the alcohol and
_very_ lightly brush from the center outwards. Change to a new
ball or pad after four or less strokes (they're pretty inexpensive).
Many optic scratches are caused by grit that has been picked-up
by the cleaning pad. If it takes more than a second or two for
the alcohol to evaporate, then you're getting the pad too damp.
After the first pass with alcohol, then repeat using the acetone.
Notice how much more quickly it evaporates, and how much cleaner
it leaves your glass.
Most important rule: Do NOT clean your glass every time you see
the slightest speck of dirt! However, if you get soft drink,
bird poop, or any other corrosive materials on the glass, do not
delay the cleaning.
Hints:
(1) Do some practice cleaning on a bathroom mirror first.
(2) If you have a seldom used, low value lens, clean it next.
(3) Take a couple of test frames with the freshly cleaned lens
and then leave it out (without lens cap) to collect some dust.
(4) As your "test lens" gathers dust take an occasional test
frame ... see just how much dust affects your pictures.
Have fun,
-Nick
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