Cleaning My Primary Mirror

Cleaning your primary optics is something they say you should only do as a last resort. I admit I haven't really noticed a degradation of optical performance, but my primary mirror has become quite dirty lately. Even though I'm good about keeping the dust covers on, dust gets in (likely some gets in when I'm imaging), and even though I rarely have dew issues here in desert Utah, I do get frost in the winter, which tends to concentrate the dirt. On top of that, I even had some dead bugs and airborne seeds down on the primary I couldn't just shake out, so a while back I decided to do some cleaning. It isn't hard to remove the primary mirror cell on the AstroTech 8" Imaging Newtonian; you just remove 6 screws around the base of the optical tube and slide out the mirror cell. It fits snugly in the tube so it takes a little prying to get it out. Here's the dirty mirror on the mounting cell after I removed it:

I've cleaned this mirror once before, after I left the telescope out the same night my sprinklers came on. That time I was extremely worried about scratching the mirror or removing coatings, so I used only distilled water applied with a spray bottle and some isopropanol to help in drying it out. I do think you need to avoid scratching your mirror, but I was a lot less cautious this time. I rinsed the mirror with tap water, applied a few drops of dish soap to the water-filled "dish" formed by the concave surface of the mirror, and after carefully washing my hands, rubbed the surface with my fingers. This took off the dust deposits nicely, with no apparent damage to the surface. I then thoroughly rinsed off the soap with tap and distilled water, and finished off with isopropanol to assist in drying, as before. Here's the resulting cleaned mirror:

I ran into a little difficulty getting the mirror cell back into the optical tube. As I noted above, the fit is pretty snug so it took some prying to get the cell back into place, with the screw holes in the cell aligned with the holes in the mounting tube. After a little effort, I got that done without dropping anything. I used a laser collimator to line up all my optics, and was ready to get back to imaging. To be honest, I have not noticed a difference in my images after going through the cleaning procedure. I imagine it would be manifest in higher image contrast, but with the galaxies I've been trying to image recently I think the darkness of the background sky is a much more important factor.