[glend (Glen)]

After spending last week at the Lake Chaffey dark site (with the heat and winds) my primary mirror was looking fairly dusty and needed cleaning. I've cleaned 12" mirrors out of the scope before but that's not as easy with a 16" mirror (especially as the GSO ones are Sikaflexed into the carrier ring in three spots (something I think is a good idea simply because it prevents mirror shift in the carrier, and prevents people stuffing up the placement and clamps and pinching the mirror on reinstall). The Sikaflex doesn't prevent cleaning, you just need to accept that the mirror will have to either be cleaned in the carrier out of the bottom tube section, or cleaned in situ.

It seemed to me that there is less chance of damage if it is simply cleaned where it is.

My approach was:

1. Prop the bottom tube section up with a strong timber under the rear steel ring to give the mirror a good tilt.
2. Get a powerful hair dryer (with cold air only) and blow off as much of the debris and dust as possible - without touching the surface obviously.
3. Place a shallow flexible baking tray (the BBQ ones are ideal) under the rear of the scope tube where the water will drain out.
4. Spray (using a clean garden or Preval aero sprayer) tap (or distilled) water over the mirror surface. I prefer to start with spraying as the pressure helps work things loose on the surface.
5. Pour distilled water over the tilted surface as a final rinse. Repeat this once more.
6. Pay attention to how much is going into the drain trays and make sure you switch them over if they become near full. Some may find duct taping a small tarp or sheet of plastic useful to avoid water going into the base (depends on your base design obviously).
7. Allow to drain, most of the water will drain out of carrier ring, and settle in the bottom of the tube where it joins the rim, and then drain into the container due to the gap between the tube and rim.
8. Once mostly drained, use a dish towel to absorb as much of the remaining water from the rear of the mirror and carrier as possible (there won't be much if you were careful when pouring the water of the surface. Wipe around the inside of the bottom of the tube (behind the mirror carrier) and clean up any remaining at the bottom of the tube. On the GSOs you can get an absorbant towel into the gap around the bottom rim and this helps get as much as possible. Don't touch the mirror surface with the towel.
9. Remove the prop and let the tube return to normal vertical position and then re-prop - this should encourage any remaining held dropslets to run off and collect at the bottom tube corner - repeat the towel process described in #8 above.
10. Allow the mirror and tube to air dry. There should have been no water on the tube above the mirror surface. You can spot grab any pesky drops on the mirror surface by touching the top of the drop with a paper towel to wick it up but this may not be needed.

Don't blow dry the mirror as this will just stir up dust in the air and it may resettle on the surface of the mirror. Better to let it dry naturally.

Photos are attached.

This probably is not a solution for some people, especially those that swear you should never clean a mirror, or those that think rust is going to destroy their scope while they sleep (as long as you dry it out properly that will not be a problem as all the parts are painted or plated). Also note that I did not touch the mirror surface with anything except water.

PS: Don't worry about your mirror fan, it is protected from the water by the way it is mounted behind the mirror on the carrier, and it should not get wet unless your using a garden hose.