A triumphant telescope-making turnabout

Two weeks ago, I found the zen in telescope making. I learned to appreciate the journey more than the destination, because I was clearly getting farther from the destination throughout that night. But this past Friday was an utter triumph. Forget the zen of telescope making; bring on the ecstasy of telescope making!

This past Friday saw me doing really short strokes for about an hour trying to fix the turned-down edge, but with little success. At this point, we collectively said “Screw it.” The turned-down edge only takes up a small fraction of an inch on a mirror that is 8″ in diameter. It’s not a big loss. After I’m completely done with figuring, I’ll simply bevel off that edge, so that all of the remaining mirror surface is correctly figured.

Once I gave up on the somewhat unrealistic goal of a perfectly figured mirror from edge-to-edge (it’s very hard to do; many ATMers simply don’t bother), I met with success after success. I switched to a wide W-shaped parabolizing stroke, doing five minute sessions interspersed with frequent Ronchi tests. I made sure not to apply too much pressure. After each five minute session, the lines in the Ronchi test were slightly more outwardly curved, thus indicating I was getting closer to a perfect paraboloid. And along the way, the abnormal hole in the center of my mirror vanished. I had the same nice curve across the entire surface of the mirror.

By the end of Friday’s session, I was so close to the correct paraboloid shape that a Ronchi test wasn’t cutting it anymore. So at the start of the workshop tomorrow, we’ll do a Foucault test, and then I’ll know where to go from there. Optimistically, I could be done with figuring by the end of the workshop tomorrow. Then, the final step with the mirror will be aluminizing it; after that, the only things left to do are — everything else! But the primary mirror is by far the hardest part, and takes more time than the rest of the scope total.

I’m so excited. All of my hard work is about ready to pay off. With any luck, I’ll be looking up at the heavens before the end of the year.

2 Responses to “A triumphant telescope-making turnabout”

  1. john Says:

    I wouldn’t aluminize it until the whole telescope is built, and you’ve test fit everything together, double/triple checked the focuser in and out distance, etc etc. THEN aluminize it, and you can mount it in the cell as soon as its comes back, greatly reducing the risk of scratching it.

  2. Cyde Weys Says:

    John: Well, the workshop I go to has their own vacuum chamber for aluminization. Immediately after the mirror is aluminized, I can simply stow it in the workshop until I get the rest of the scope built. So I don’t really see how there’s a risk of scratching it.