Cleaning mirrors
When you clean a mirror, take special care not to damage the fine optical surface. The mirror’s thin coating of aluminum is extremely soft, especially when compared to abrasive dirt, and you can gouge it easily.
Cleaning a telescope’s primary or secondary mirror typically requires you to remove it and the cell that holds it in place from the telescope. Consult your owner’s manual for specific instructions.
With the mirror lying on a table, use compressed air to begin the cleaning. Don’t use a brush for this step, to avoid any possibility of damage.
Next, inspect the mirror’s coating for pinholes and scratches. A good coating can last 10 years or longer if the mirror has been well cared for. To check it, hold the mirror, reflective side toward you, in front of a light. It’s not unusual to see a faint bluish image of the light through the mirror if the source is bright, but its image should appear the same across the entire mirror. If not, there may be thin, uneven spots in the coating.
Any scratches or pinholes in the coating will become immediately obvious, as well. You can live with a few, but if scratches or pinholes abound, or if you detect an uneven coating, you’ll want to send the mirror out for recoating.
If the coating is acceptable, bring the mirror to a sink. Be sure to clean the sink first and lay a folded towel in it as a cushion just in case the mirror slips. Gently run lukewarm tap water across the reflective surface. This should lift off any stubborn dirt particles that refused to dislodge themselves under the compressed air.
Next, fill the sink with enough tepid tap water to immerse the mirror and add to it a few drops of gentle liquid dish soap. Carefully lower the mirror into the soapy water and let it sit for a minute or two.
With a big, clean wad of surgical cotton, sweep across the mirror’s surface ever so gently with the backward rolling motion I described earlier, being careful not to bear down. Roll the cotton a half-turn backward, discard it, and use a new piece. If stains remain after this step, let the mirror soak in the water for five to 10 minutes and repeat the sweeping with more new cotton.
With the surface cleaned, drain the sink. Run tepid tap water on the mirror and its holder for a while to rinse away all soap. Then turn off the tap and pour room-temperature distilled water across the surface for a final rinse.
Finally, rest the mirror on a towel and let it dry. I usually rest it against a pillow on my bed. Tilt the mirror at a fairly steep angle (greater than 45°), its edge resting on the soft towel to let any remaining water droplets roll off without leaving spots. When it’s dry, insert it into the telescope, collimate the optics, and you’re done!
More tips
Other telescope parts also require occasional attention. For instance, some focusers tend to bind if you don’t lubricate them occasionally. To prevent this from happening, use a little Teflon lubricant on the focuser’s small pinion gear or roller. Loosen the screws (typically two) that connect the plate to the side of the focuser’s housing. Squirt a tiny bit of lubricant on the pinion teeth, tighten the cover plate, and wipe off any drips, as required.
If a metal telescope mount starts to bind, lubricate the axes’ bearing points. Some manufacturers recommend this be done at specific intervals, while others make no mention of it at all. If the latter is true, then do it once a year.
The Formica and Teflon materials in most Dobsonian mounts require little in the way of maintenance. But if your Dob doesn’t move freely, take the mount apart and apply a little furniture polish or car wax to the contact surfaces. Buff, reassemble the mounting, and try it. You should notice the difference immediately. If not, consider replacing the pads with furniture slides, available at most hardware stores.
Some drives also need an occasional check to keep them happy. Carefully remove the protective housing and put a little light grease between the two meshing gears. While the drive is open, put a drop or two of thin oil on the motor’s shaft, as well. Then reassemble the drive, turn it on, and listen for any noises.
Most clock drives hum as they slowly turn. If yours seems unusually loud or if grinding noises are coming from it, turn it off immediately and contact the manufacturer for recommendations.
The bottom line
Even after lots of use, caring for your telescope doesn’t take much effort. If you show it even a little love by storing it correctly and performing periodic maintenance, it will happily show you the wonders of the universe for years to come.