Over the years, I’ve written extensively about cleaning optical components. The first thing to understand is that mirrors have to get pretty dirty before the performance of the telescope starts to noticeably degrade. It feels good to have a pristine, “like-new” looking mirror in your telescope but from what I can see from your photos, your mirror wasn’t in a serious need to be cleaned. My telescopes sit outside virtually every night in Chile where it is pretty dusty and they get pretty filthy between my annual maintenance visits. I see virtually no degradation in imaging performance—even when the mirrors are coated in a layer of grime. Star halos may be slightly more pronounced due to more scattered light but even that effect is barely noticeable.
The good news is that the silicon-monoxide overcoat used on most aluminum mirrors is pretty durable so, if you are careful, cleaning shouldn’t scratch the mirror. On my systems in Chile, the dirt will be so thick that the first cleaning step is to soak the mirror with cleaning fluid and to lay Kleenex tissue (Kim Wipes also work well) on the surface. Lifting the wet tissue from the surface without any wiping motion lifts the loose stuff from the surface. The the mirror is then soaked and the surface dabbed with clean tissue. I keep a trash bag nearby and change the tissue with every dab. I might spend 15 minutes soaking and dabbing until the tissues are no longer lifting any material from the mirror. At this point the mirror looks worse than when I started.
The next step is to use a folded tissue soaked in cleaning fluid in a gentle rolling motion to very lightly wipe the surface. The idea is to avoid wiping the surface with any dirt imbedded in the tissue. Again, I use a LOT of tissue to gently do a rolling wipe over the entire surface. At the end of this step, the mirror should be clean and free of debris and the trash bag full of a lot of dirty tissue.
The last step is to polish out all of the streaks and haze that remain. Again, using only new, clean tissue,I use a very fine spray of cleaning fluid and lightly polish the surface in small areas to a perfectly clean finish. When I’m done, the mirror will look like new.
Finally, what’s the best cleaning fluid? The OP reports using Zeiss lens wipes and reported they worked, but in my view, they are more suitable to eyeglasses than cleaning larger components. When I spent some time working at Celestron, I learned that they typically use acetone to clean their mirrors and that can work well, but I’m no longer in favor of that idea. First, acetone isn’t good to use inside and it is VERY flammable. Second, it will immediately dissolve paint and any plastic that it comes in contact with. Third, while it is a very good solvent for grease and oil, it mostly just serves to dissolve oils, spread it around and then quickly evaporate to leave a worse problem than what you started with. And finally, acetone dissolves paper produces like tissue. It’s bad for your hands, bad for cleaning, and bad for most wipes. So, why does Celestron keep doing this? Acetone is ultimately a terrible choice for cleaning most components.
I’ve found that the best cleaning solution is to mix distilled water 5:1 with reagent grade isopropyl alcohol (that you can order through Amazon). I mix it in a new plastic spray bottle from Home Depot. These bottles have a continuously variable spray pattern and that makes it very easy to control how much fluid you distribute on the surface. Using chemically pure alcohol and distilled water eliminates the possibility of leaving any residual film on the surface. Some folks like to add 1-2 drops of dishwashing liquid to the mixture simply to reduce the surface tension of the solution. I don’t think that’s necessary and it adds yet another thing that can create a film so I don’t recommend that approach.
NOTE: NEVER use rubbing alcohol to clean optics! Rubbing alcohol contains only about 70% alcohol along with oils, scents and other stuff that’s not good for your glass. The other choice that often generates controversy is the idea of using a commercial window cleaner such as Windex to clean optical surfaces. Many window cleaners contain ammonia and other ingredients designed to remove calcification. Ammonia attacks many optical coatings and it is not a good thing to use on precision optical components. Windex can also leave a film or haze on the surface—depending on how it dries and how it is polished. My advice is to NEVER use Windex on any optical components. There is nothing more effective or cheaper for most optical cleaning tasks than water and isopropyl alcohol.
John
