Cleaning your reflecting telescope's primary mirror (YouTube video) - Forums

Topic starter

Oct 8, 2023

I have produced a video detailing the process of washing the primary mirror of my 8" RC. If you have another type of reflecting telescope, the nitty-gritty of removing and reinstalling the mirror will be different, but you might find the washing part of the video useful anyway. You will find the video here: https://youtu.be/ztDfTDpuI38

Cheers and CS
Flemming

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GregLatiak

Oct 8, 2023

When I was looking for information on the proper cleaning of my RC 6" and 127mm Mak, I discovered a publication by SPIE - the society of PhotoOptical Instrumentation Engineers on the proper care of optics by Robert Schalack. ISBN 978-0-8194-9457-3. Was very helpful in guiding my cleaning of the mirror and lens surfaces in these telescopes. I would have liked to have a video on how to take the scopes apart and reassemble after cleaning – but at that time very little visual guidance was extant. The book was purchased as a PDF and converted into Kindle format. Was quite technical – I found it helpful.

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Stephan Linhart

Oct 9, 2023

Thanks for making this Video. I am sure it will help others.

I want to highlight two potential issues.

One is taking out the secondary mirror on a RC telescope. Since it is aspherical, positioning of it is extremely crucial and very hard to re achieve once out.

I you have to take it out, mark the position of the Mirror. When re-assembling align this marking and put the three collimating grub screws exactly in the small dents they caused when fastening.

A friend of mine did not do that and we spent 3 full days to fix it.

The second is drying the mirror.
Maybe it is just me, but I wouldn’t dare to put the mirror face down on a towel.

What works well for me is just blowing the remaining waterdrops over the edge away with a blower similar to yours.

There are no remains visible on my mirrors doing it this way.

Best regards,

Stephan

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Flemming Kristensen

Topic starter

Oct 9, 2023

Hello Stephan.

Thank you for your comments, it's always good to share in the experience of others, and I'm by no means thinking that mine is the only way.

Putting everyting back exactly as it was is sound advice, and maybe I should have pointed this out in the video. I have marked the secondary holder with a black permanent marker (yes it is visible) back when I installed the heater, and now of course, I know along which vane I want to route the wires from the secondary holder to the edge of the tube, so I orient it more or less by feel.

With regards to the drying of the primary, that should always be a matter of personal preference. I don't think the surface of amateur telescope mirrors are that fragile though, after all they receive a hard coating from the factory, but I make sure never to wipe them dry. By placing it face down on a soft surface (the dishcloth is resting on a soft bath towel) I make sure that I dont accidentally introduce any rubbing motion, so I'm comfortable with that. Using only the blower is, of course, ideal if you can pull it off but I failed to get that right on a previous occasion where I also made the mistake of using tap water.

Best regards,
Flemming

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Mike Hamende

Oct 9, 2023 · Edited: Oct 9, 2023

I like to see how others clean their mirrors. When I first needed to clean a mirror after a few dewing events causing haze in my images I found a lot of dos and dont's, no procedure was the same. A lot of people would say "Never clean your mirrors!"

The method I've been using is fairly simple especially if the mirror is small enough to be held confidently during the process.

I first use a blower to remove large particles and fibers. Then I'll take the mirror to the sink and rinse the mirror under tepid water for a few minutes. If there are stubborn spots I'll use cotton balls wetted with a mild dish soap solution to wipe from the center out while rotating the cotton ball into the stroke to constantly expose new fibers to the mirror and prevent dragging grit across the mirror. Use a new cotton ball after each wipe. Alternatively, I've simply washed my hands very well and used finger tips to gently "scrub" the mirror with a mild solution of dish soap, rinsing often. Finally I'll rinse the mirror with distilled water. If you hold the mirror at a steep angle and pour the water smoothly from top to bottom you can get most of the water to roll off of the mirror in sheets. Any remaining drops I dab with Kim wipes.

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