Sunday, August 8, 2010

Telescope repair

Well, repair isn't quite the right word. But I got the damn thing to work a let better now.

I wasn't working with my big 8-inch reflector; it's in perfect shape. But it's big and heavy, and a pain to bring outside. I can't take it out for five minutes to look at Jupiter; if I'm bringing it out, I'll be out for an hour or two.

No, I was working with my other 'scope. It's a small (60mm) and not terribly good-quality scope, a gift from my dad's coworker who no longer wanted it. It's not bad; the main lens is good quality and achromatic (uses two types of glass to minimize false-color images) and the tripod is good and sturdy. The long-focal-ratio design means that the economy-quality eyepieces work decently well. But, it had some problems.

First, the focuser. It's made of plastic, and a number of the rack-and-pinion teeth had broken off. It barely worked. I disassembled the whole thing, and took the back of a knive and cleaned out the teeth. Removed lots of gunk, broken teeth and bad grease. Reassembled, tightened, not perfect but waaay better.

Next, the bearings. It was originally intended to be a go-to telescope, with a neato little electronic controller. Well, I'm too much of a purist to drop a benjamin or two on something I can do myself, so I don't have the fancy controllers, and I took off the motors attached to the scope a while ago. The problem is, the left-right and up-down motions just kept getting worse. Either too loose, or too-tight and jerky. No good. I couldn't track stuff that way.

So, I took it apart. I mean everything. The entire altitude bearing. End knob, tension washer, washer, gear, washer. Then I saw the problem. The motor assembly (which includes a worm gear that turns the gear than moves the scope) was attached by three tiny screws. One of them was not tightened. Tightened it up, reassembled, all systems go. Loosen the knob to move quickly; tighten and turn a handle attached to the worm gear to close in on or track objects.

Azimuth (left/right) movement had a similar problem. I took it apart, to discover it was MISSING a screw. Somehow, it had been assembled msising an important little part. I found a matching screw in my junk box, and that fixed it right up. The motions are all rock solid now.

Finally came the finderscope. It's a pretty cheap scope; the lens is plastic. Terrible optical quality; looking at bright stars or the moon results in colored reflections. But the more pertinent problem was that it was misaligned with the main telescope. So I aimed it at a mailbox down the street that wasn't in line with a house* and centered it in the main scope. Adjust finderscope, check main scope, repeat. Ten minutes of tedious work, and I got it perfectly dead centered. Aligned the crosshairs on the top of the post, and it's right in the eyepiece at 175x magnification.

For a comparison with similar fields of view, what I was doing was akin to looking through a mailing tube, and then switching to one of the tiny hollow coffee stirrers. It was actually pretty impressive.

Now, off to observe!

* This was the result of me going up to my mother and asking "On a scale of one to serial killer, how creepy would it be to take my telescope out and watch the mailbox down the street?"

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