TheSkySearchers

I tried imaging M-45, the Pleiades, last night, but the haloes on the bright stars were out of control. Time to clean the mirror, methinks. Once every twelve years is probably not too often, whether it needed it or not.

Anticipating this, I attended a mirror cleaning workshop at this year's star party. It wasn't hard at all. Here's a before and after pair:

There's another clear night forecast later this week, so I'll re-run the M-45 series and maybe post a before and after pair of them.

What a difference!

I don't even clean my glasses more than 1-2 times per week - others are compulsive about it. Somehow I got used to it...

Was recently party to the cleaning of a 30 inch mirror (30 inch Obsession at Morning Calm Observatory)! Cleaning was simple. Removal and replacement of the 110 lbs of glass was the hard part!!

Dave

Nice clean-up, Kathy. It did look due for it to me.

I'll be interested to see the before-and-after M45 imaging results if you go that route. I've cleaned my mirror once in the 10 years I've had the scope. It was scary to approach, but the actual cleaning was pretty straightforward.

Bob

Yeah, quite honestly it is best to clean them at least once a year. More if you are out a lot or the mirror is in a truss-style. That one definitely needed it though Kathy! In fact my 17.5 is in need a cleaning as we speak! It doesn't take much "stuff" on there to impact the views (or images).

For those that are a little afraid to clean their mirrors out of fear of damaging them, I have always used the following method and never had any issues. Just approach it slowly and methodically and you will be fine.

SparWeb wrote: ↑Tue Nov 01, 2022 2:59 am What a difference!

I don't even clean my glasses more than 1-2 times per week - others are compulsive about it. Somehow I got used to it...

I had to laugh out loud as I read your comment. My wife and I just had this discussion. I too only clean my glasses about twice a week...unless one of the dogs jumps up in my lap and decides to slobber on them! She is constantly cleaning her glasses, probably 5-10 times daily. I joke that she's going to wipe off any coatings on her lenses!

Unitron48 wrote: ↑Tue Nov 01, 2022 11:44 am Was recently party to the cleaning of a 30 inch mirror (30 inch Obsession at Morning Calm Observatory)! Cleaning was simple. Removal and replacement of the 110 lbs of glass was the hard part!!

Dave

30inch Mirror.jpg

That's a beast!

Here is a before-and-after pair, showing the results.

These are stacked masters. The dirty stack consisted of 24 subs at 300s. The clean stack was 6 subs at 300s. (Fewer subs because I ran the series later at night to avoid most of the moonlight and ran out of time before dawn.)

I did a linear fit to equalize the dirty image to the clean one. I then used an STF stretch on the clean image, and applied the same histogram to the dirty image.

Dirty mirror:

Clean mirror:

Interesting result. TBH I wasn't expecting such a noticeable difference, but clearly the clean mirror produces a better result, even with less time on target. It might be time for me to peer down the OTA again!

Bob

bobharmony wrote: ↑Fri Nov 04, 2022 1:52 pm Interesting result. TBH I wasn't expecting such a noticeable difference, but clearly the clean mirror produces a better result, even with less time on target. It might be time for me to peer down the OTA again!

Bob

I guess 12 years of accumulated crud will do that!

Larry 1969 wrote: ↑Fri Nov 04, 2022 10:48 pm I find myself in need of a good mirror cleaning as well. Do you have any advice?

It's not hard. You will need some distilled water. You can buy it in the supermarket here. Use a clean wash basin. (I used a new kitty litter box.) You will need some makeup-removing pads, and some rubbing alcohol.

Start by blowing loose dust off with a bulb blower. Then rinse under a running tap. Avoid contact with any object: just the water. In the basin, cover with tap water and add a few drops of dish soap.

With the surface of the mirror submerged. lightly drag a makeup pad over the surface of the mirror. If the pad has a soft and a coarse side, use the soft side. Use no pressure at all. Let the weight of the pad do the work. Make one wipe from centre to edge. Then throw away the pad and use a new one for the next wipe. Continue, using a new pad for each wipe until the entire mirror has been done. Pour off the soapy water.

Rinse under the tap to remove all the soap. Then rinse with water that has a few drops of rubbing alcohol added. Finally rinse with distilled water. (I didn't have any alcohol, so I skipped that step and did an extra rinse with distilled water.)

Stand the mirror on its edge to let the water drain off. If there are still significant drops beaded on the mirror after a couple of minutes, use the corner of a paper tower to wick them away. Touch the paper to the water without touching the glass. Then let it stand until dry.

There are plenty of videos on the net describing how to do it. What I described is how it was taught to me at the summer star party.

So you left the mirror in the mirror cell? That's the part I was worried about.

Larry

Larry 1969 wrote: ↑Mon Nov 14, 2022 10:47 pm So you left the mirror in the mirror cell? That's the part I was worried about.

Larry

Oh, gosh, no! I opened up the mirror clips (two screws each) and lifted the mirror out of the cell. You don't want to have water damage on the steel bits like screws and springs. I returned it to the cell before I took the 'after' picture.

Tightening the mirror clips, you have to be careful. Do not use an electric screwdriver! You have to tighten the screws by hand so that you can feel when the clip makes contact with the surface. Stop immediately. It is just contact: there is no force on the mirror at all. Some people say there should be no contact. I am not sure I agree, but certainly you want no more than just contact.

I was always taught the clips are tensioned just enough that a very thin sheet of tissue paper can still slide between the mirror and clip. Any tighter and you will pinch the optics. That's just how I was taught, may not be correct.

AstroBee wrote: ↑Mon Nov 14, 2022 11:09 pm I was always taught the clips are tensioned just enough that a very thin sheet of tissue paper can still slide between the mirror and clip. Any tighter and you will pinch the optics. That's just how I was taught, may not be correct.

I've read about "pinched optics" and never really understood it. Are they saying that you actually distort the glass? That's hard to believe...

Larry

AstroBee wrote: ↑Mon Nov 14, 2022 11:09 pm I was always taught the clips are tensioned just enough that a very thin sheet of tissue paper can still slide between the mirror and clip. Any tighter and you will pinch the optics. That's just how I was taught, may not be correct.

That’s my thinking too.

I always use a playing card or business card to space them.

Lady Fraktor wrote: ↑Tue Nov 15, 2022 4:59 am I always use a playing card or business card to space them.

That gives extra margin against differences in thermal expansion causing too tight contact, I think.

Here you go FWIW.

https://www.astronomyclub.xyz/spherical ... ptics.html

JayTee wrote: ↑Tue Nov 15, 2022 6:32 am Here you go FWIW.

https://www.astronomyclub.xyz/spherical ... ptics.html

Yep. That's good FWIW.

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I liked the guy breaking down the coating to something that I could understand...
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In a way... from what he said... it's like cleaning the plastic on a CD...
Your not cleaning the reflective part... your cleaning it's clear coat...
( By the way... Mothers Aluminum polish fixes CD's... Polishes that plastic for the laser to do it's job...DVD's too ) Headlights etc.
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If it didn't have the clear coat , it would Oxidize and DULL fast.
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My Grandson was here last weekend , we were going over some of the telescopes...
He was getting "Hands on" with the 10" DOB....In the day , warned about the Sun...IF IT WAS OUT...
Then there was some Mirror safety... and colmination....
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Whoa , Colmination was off , I had him mess with the three thumb screws a little...
But then I looked at the mirror surface....hmmm, I gotta clean it anyway.
So we played with the give and take of colminating...
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One thing I will add to this video preparation...
For one finger typers like me...Yes... I don't work in a office.
My Hands aren't silky smooth... In fact , I bet SOMETIMES... My skin could CUT yours...
My point it... my hands aren't always extremely bad... But for something THIS delicate.
I need to think of that , Sandpaper is a good start before getting things wet to soften the skin.
the presoaking of your hands are gonna depend on there condition AT THE MOMENT.
My hands would need more prep in Winter rather than Summer...
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He talked about rinsing with distilled water.... RO water should be next best... we have a little facet for that.
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Thanks for the discussion on Mirror mounting also.... I'm sure I have it too snug ? I really don't remember.
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Something I will add.... Isn't Glass "FLUID"...? Just Very Very slow...
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Anybody know about Glass ""Sagging" over time...even if it's OLD Recipe glass... it's glass.
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Gotta Fly...
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PS I'm noticing there is a "Window" .... I can't use hand moisturizing lotion...
So after a Hot shower and a little pumas stone , my hands are in pretty good condition to wash the mirror.
I feel them drying fast...
So when I clean mine , I should have it out and in a safe place.
I think my hands need a little more prep...and sandpaper.