I just picked up an old ('50s era?) reflector telescope. Really solid cast iron alt/azimuth mount, no dents in the tube, used to be a high school telescope. The mirror looks a bit clouded, I expect to have to replace it. Still should be able to see something through it… What I can see in daylight is a dark circle with a light crescent at the top.
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I don’t know how to set it up, align it, etc. Can anyone here point me to a reference or two? Alignment procedures, that sort of thing?
Thanks
Since the mirror is a first-surface mirror, that is, the reflective material (usually alumimum) is subject to exposure from the elements. You can try breathing some life back into it with a soft polishing cloth. However, ultimately, assuming the glass itself isn’t too badly scratched, you’ll want to have the old alumiminum coating stripped off, and a new one vacuum-deposited. This will be a lot cheaper than an entire new mirror, and it will also ensure that you’ll retain the original optical properties, especially focal length.
As for alignment, the procedure is called collimation, and you can find some good information about it here. Good collimation is critical to the perfomance of a Newtonian reflector.
Yeah, nice disjointed sentence there. :smack:
Eight minutes. Thanks, Q.E.D!
Alright… Anyone got a lead on re-aluminizing the mirrors?
You can try [http://www.majestic-coatings.com/]Majestic Coatings. They do aluminum coated, silicon monoxide protected primaries up to 24" diameter, starting at $75.
Oops. Fixed link.
Do you have a photo you can show us? If you don’t have a server to put it on, the message board on Cloudy Nights allows image uploads and also has a lot more astrnomy people than here.
Don’t try to polish the mirror. Just get it recoated. But first we should figure out if it’s worth spending that money on.
No picture (yet), and I can’t find any identifying labels with the exception of an “Edmund Scientific” label. But I can give a fairly detailed description: The secondary mirror is mounted on a single steel rod rather than a “spider”. Said steel rod is slightly bent, BTW. I expect I’ll have to replace at least the steel components of the secondary mirror. Overall length about 4 feet, diameter is 5 inches. The mount is made of cast iron and steel, very rugged. Upon measuring, I note that the primary mirror end of the tube is slightly out of round. This and the bent rod at the other end no doubt account for my problems.
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As to being worth spending the money on, I got it essentially free. I’d like to hope that it would cost less to rebuild this one than to buy a comparable new one in addition to which I rather like older stuff. And I don’t have to worry about voiding the warranty…
The telescope you describe sounds like a 3" one I had in the early 60s. Got it from my grandfather, who I think used it himself (but not sure).
Edmund sold a 3" scope (that would be the diameter of the big mirror), also I think a 4.5" scope. Your tube diameter sounds in between these two sizes to me, but memory is foggy. Is the mount made of metal castings with black wrinkle finish paint, and 3 legs that each have two wooden struts of about 3/4" square stained a sort of a dark cherry wood color?
The simple Newtonian scope does a beautiful job of collecting light and forming a nice image out of it. I think Newtonian telescopes represent some sort of elegant high point in the history of technology.
Wrinkle finish light barf green paint on the legs, which are held on with a singe wingnut each. Rotation scales have white markings on a black plastic disc. Each disc has 2 indicators which look like galvanised nails. No wood whatsoever.
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Guess I’m going to have to take a few pictures…
Yes, please do. And don’t listen to scr4. 
He’d be giving excellent advice if it was a new and expensive mirror, but since you want to get an idea of the 'scope’s performance before sinking any significant amount of money into it, you ought to try (gently) to polish the mirror a little. You might damage the finish some, especially if it’s uncoated Al, but that’s moot at this point, anyhow. You won’t damage the underlying glass one bit, as long as you use something like canned air dust spray to blow off any potentially abrasive particles first. When you’ve got something resembling a reflective surface to work with, do the collimation procedure as outlined in my earlier link, then use the 'scope to look at some bright stars. If it seems to produce a good image (You may need to clean the eyepiece, too), you can then consider whether to further restore it.
Wrong. In better light and after a bit of a wipe off, it’s actually grey. Just in case that makes a difference.
OK, I took the mirror out today for a closer look. It’s 4.1/4" and covered in a filthy thick layer of dust. Looks really nasty. Air has not removed the majority of the rather sticky dust; guess I’l have to try something else. The good news is that it doesn’t look too bad under the dust. Any suggestions? Soapy water? Ammonia? Alcohol?
By the way, now that I’ve done a bit of research rather than just trust the guy I got it from, I can tell you that it’s got an equatorial mount, not alt/azimuth.
Not sure what to advise you on the mirror but I might try soapy water and a camel hair brush with a very gentle touch to loosen the dust then rinse well with DI or distilled water to air dry without spots. I can’t guarantee it won’t scratch the front surface but it probably as gentle as you can get.
The equatoral mount is good news. It will seem clumsy at first but once you align it to true north you need to only move the mount in right ascension to track objects as the earth rotates.
Sticky dust usually means oils or tars, (possibly cigarette smoke buildup, or polymers from the painted barrel of the scope?). An alcohol (ethanol) soak is pretty good for that. If that doesn’t work, I’d be tempted to try one of those orange oil cleaners. I’ve never done that on a mirror, but it should be fairly gentle.
An hour in soapy water (use cheap dishwashing liquid without hand-saving glycerin, or a “pure” soap) is likely to help a lot. The idea is to get as much of the crud loosened up and gone as possible, before resorting to brushes.
Ammonia is a BAD choice. It’s too basic, and could well damage the coating.
I’ll give it a go in soapy water in the morning, possibly followed up w/ alcohol to clean any soap residue. Thanks to all for the advice.
Just cleaned it off w/ soapy water, rinsed in distilled water. I hope the drops and runs dry clean. No scratches that I can see; now that it’s clean it’s amazingly perfect. I put it in the kitchen floor below the overhead light, and it’s dazzling like sunlight 5’ above the floor.
Now I just have to figure out how to collimate that thing and set up the mount.
Thanks to all for the replies!
For those out there who care, I took this scope out tonight and looked at the moon. Unbe-freakin’leivable! Even my kids are impressed. Thank you all for you help!
And now, one more thing. Anyone know a good trick for someone as ridiculously underequipped as me to set up the equatorial mount accurately?