Greetings friends. I recently acquired a telescope. It is nothing spectacular, but I believe it will prove to at least be as useful as my binocs, and perhaps will make a decent steppingstone until I get my 10" dob.

At any rate, this is a simple Tasco Galaxsee Newtonian reflector on an Equitorial mount (hey, it was free). Now here is the issue. The person that previously had this, set it up, took it out once, decided they could not see anything and then brought it back in and set it in a corner for a significant period of time, with no eye piece in it and with no lense cap on it. So needless to say, the optics are rather dusty.

So I ask, before I completely take it aprt, what is the best practice for a thorough cleaning of the primary and secondary Mirrors on a newtonian reflector? Yes, I am googling this as well, but I figiured I would stop here and ask as well.

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Eagle Eye Observatory

I would suggest that you first get some "canned air" and see how much dust you can blow off the mirrors. That may be all you need to do.

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T. Anderson

ok that will be a good start. I suspect, with the dust build up on it, it will take more though.

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Eagle Eye Observatory

The dust will have little or no effect on the image. Don't worry about it beyond blowing of the worst. Paranoid people have been known to gently wash mirrors upside down with very gentle water - but it's not worth it and besides you'll never get the mirror out of that telescope (or if you do you'll never get it back and recollimated). Note, I'll take a filthy corroded collimated telescope over a clean telescope with badly aligned optics

When you lose more than 30% of the aluminium surface - that's the time for action.

aluminium? Are you from the Snowden portion of the eastern Ozarks?

Meanwhile dust absorbs light thus reducing the reflectivity of the surface it's on. This hinders light-gathering power. It also scatters light (check out light beams in a smoke-filled room) and thus affects resolution. Clean optics are accurate optics. Dawes Limit doesn't apply to mirrors covered with dust.

Somewhere way back Phil recommended certain techniques for cleaning first-surface mirrors. I sort of remember distilled water and a mild alkaline agent being primary ingredients.

Re a Tasco I doubt there was much attention paid to collimation in the first place.

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Maksutov,

Granted dust will reduce and scatter - but so what if you lose 10% of the light, 0.1-0.2 mags is not worth getting worked up about. The owner of a beginner level instrument should not be encouraged to start taking it apart. The Dawes limit is not a useful concept for a backyard telescope - theoretically a 130 mm mirror could split 0.9", now find one that does.

On the subject of aluminium - IUPAC recognises Humphrey Davy's third attempt to name the element with recognition that the ACS has differed since 1925. Personally why "alumium" never caught on I'll never know... (H Davy's first name for the stuff)

That's an interesting transformation. Now, having built reflectors from scratch since 1961, I can see the difference, both in brightness and resolution, in the image of a clean optics scope versus a dirty one. Why not? It's a good way to learn about the pluses and minuses of scope construction. As well as the basics re telescope optics. The "beginner" might realize "Hey, I could do a better job myself!" and get into telescope making, a fine pursuit that has led many into a career in astronomy. Got one right here. Made it myself.In the US it's aluminum. Quite elementary.

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Couldn't find the BA's post re cleaning, but there's this from the AAAA.

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Agreed that the ACS (American Chemical Society) decided that it was aluminum in 1925 and this is the common use in the US. However the rest of the world uses the IUPAC recommended spelling - aluminium. Although I did attend Missouri-Rolla, I still belong to the rest of the world.

PS - With the growth of US Spanish, are the Americans going to start using aluminio? or will the ACS invent alumino?

ok so lets put some of this stuff to rest. First, Yes, I am a beginner. In that I have been using binoculars for seveal years, waiting on a scope purchase so that I can be sure I do not comprimise what I want. Second, I have no issue with taking something apart to see how it works if I am relatively sure I can get it back together. I have looked at this scope and it isn't going to take a rocket surgeon to work on it. Third, I want it clean. Whether or not it matters is irrelevant. I want it clean and asked for the best practices in cleaning the optics.

Thanks for the link, I will check it out.

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The More I learn, The More Ignorant I Become

Eagle Eye Observatory

Here's how I cleaned my mirror from my 10" Orion dob:

1) Remove mirror from mirror cell
2) GENTLY run a slow trickle of water to float off any lose particles (may actually want to skip this step)
3) Put a gallon or so of distilled water (enough so that the mirror will be submerged) in a CLEAN sink with a drop or two of soap
4) Place mirror on folded towel in sink, let soak for 1/2 hour to loosen debris
5) LIGHTLY drag a cotton ball (real cotton, not the polyester ones) ONE PASS across the surface of the mirror while it sits in the water. The weight of the wet cotton ball is enough pressure on the mirror.
6) Repeat step 5 until you have cleaned the surface of the mirror. Use one cotton ball per pass on the mirror, use another one to make another pass next to the first pass (like mowing a lawn) and go across the mirror, not around it.
7) Lift mirror out of water, use either tap or distilled water to GENTLY rinse mirror. If your mirror is clean, the water will sheet right off when you tilt the mirror. If any small droplets remain, use the corner of tissue paper to gently soak them up.

FWIW, the one time I cleaned my mirror, I thought it was just dusty, but there was in fact a light film on the mirror as well, the above method took care of that nicely.

Thanks redshifter, I will do that tonight.

On another note, there should be an "Optics Care" sticky at the top of this forum

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Eagle Eye Observatory

Well I first used canned air and that got a lot of the stuff off, however there was a cloudy film over it. I removed the entire cradle that contains the primary from the tube assembly.

Next, I took a pencil and numbered the rubber mounts holding the mirror in place and placed matching numbers on the side of the glass next to the mounts.

I then removed the mirror and placed it in a clean bowk of distilled water and let it soak for about 10 minutes.

After it soaked, while it was still submerged, I ran single passes with a ball of cotton. I did 3 series of passes in different directions.

I placed the mirror back in the assembly, then placed the assembly back in the tube, matching all holes with the numbers I had marked


Now I took it outside for (my) First Light. we have a lot of trees and there are scattered clouds out, so the moon was about all I could see. I did manage to see a couple of stars and one has a spikey, rainbow type halow around it, so I imagine I need to collimating it. I shall probably attemt that tomorrow night.

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Eagle Eye Observatory

3 series of passes is probably overkill. Anytime you're messing with a mirror, you're running the risk of scratching it, so be careful. You shouldn't clean your mirror more than once a year max.

Also, make sure you don't tighten down the mirror cell clips too much, they should be just barely clamping down on the mirror.

the reason I made several passes was because it looked like there was some type of film on the mirror. the first pass didn't clean it well. I am assuming there weere either smokers in the house or a grease fire at some point. The first and second passes left streaks in the film, third pass got it clean.

At any rate, thanks for the top on the clips, I did tighten them down a bit so I will go loosen them up.

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Eagle Eye Observatory

Lens dust brush is a nice accessory. They remove about 98% of the crud. Just be sure and clean it regularly. An occasional windex type spray won't hurt so long as you let it dry and, again, use your soft brush. It will break the bond between air borne contaminants and the lensing surface letting you brush them away. Try to resist the urge to polish your optics with your shirt. Wiping of any kind is very risky. This is how most optical surfaces get scratched.

I wouldn't recommend windex (or any other generic 'glass cleaner') on astronomical optics. For eyepeices or any other coated or multicoated glass surface, only use cleaner specifically designed for multicoated optics, unless you're cleaning a mirror, then use the method described above. IIRC commercial, over the counter glass cleaners can easily damage the coatings on eyepeices, binocs, etc.

Yeah I won't even use windex on my tinted motorcycle helmet face sheild. It can leave definite discolorations on the reflective surface.

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The More I learn, The More Ignorant I Become

Eagle Eye Observatory