If your telescope is used and stored properly and if your observatory is not in the middle of a
woodland (where resin droplets are inevitable) it should be really unusual to go beyond the "camel
brush and compressed air" level. Remember, even if the color of the lens coating changes a bit,
has a local "flourish" or a small scratch, this has no detectable effect on telescope performance.
8.3) Clean the mirrors
Before you start…:
Are you sure your mirrors really
needs cleaning? It is not easy to give a general rule,
but a mirror has to look really "horrible" before you
notice
any
performance degradation. The mirror at
right, for example, is a reasonable candidate for
cleaning with air, but not for a "bath". As a very
general rule, a mirror requires cleaning every 100-300
hours of use, but this number is strongly dependent
on conditions.
Anyway, do not expect the performance of the optics
to change significantly just becasue of cleaning!
We suggest to clean your mirrors ONLY WITH COMPRESSED, FILTERED AIR, LEAVING
THEM IN PLACE IN THE TELESCOPE STRUCTURE. A compressor with a good filter is a
safe, good and fast solution for "regular" dirt and dust. You can use cans of compressed
air (with no liquid propellant). Only if you think your mirror needs a stronger action read
further – and proceed AT YOUR OWN RISK. Damages due to improper cleaning are not
covered by warranty
To
wash
your mirrors have handy the following equipment:
Distilled (de-ionized) water (buy a couple of 2-liter bottle)
Air blower (can with no liquid propellant or an air compressor with
filter).
Kitchen transparent film and paper tape.
Latex gloves and a mask (to avoid spitting on the mirrors)
Sterile cotton . You can buy it in a pharmacy. You need sterile cotton
since it’s more likely to be grit free (there are no "microscopic sand
grain" in it).
A solution of 100:1 diluted mild dish detergent in distilled water, if
needed (see procedure)
A water atomizer (see photo at right) with distilled water, if needed
(see procedure). Buy a model that permits also water "jets", not only
atomization.
A lot of paper towels (the roll you usually have in the kitchen is ok). You will use them to
dry the excess water from the mechanical part of the cell – not form the mirror itself.
To work on the primary mirror, you will need to disassemble the cell from the structure of the
telescope. Simply unscrew all the screws that keep the cell in place. Before to do so:
"Lock" very hardly the telescope mount. When you remove the primary mirror, the
telescope is totally unbalanced! In equatorial type mounts, point the scope to the pole. In
alt-az mounts, point to the zenith. This position will limit the stress on the mount when you
remove the primary mirror cell.
38
