by Richard Ozer
Just in time! I finally finished my daughter's 6" dob... she did the mirror grinding; I did the polishing and figuring; she picked out the color; and I did the woodwork. It's a midget twin of my 10"... and there's alot to be said for a scope that weighs next to nothing.
Unlike my 10" aluminum scope, the tube for the 6" is made from phenolic (often used in model rocketry). Phenolic is a great material for telescope construction; far superior to sonotube in my opinion. It's very light, easily machined, and has very low moisture absorbtion. We coated it with a metallic navajo-blue paint, which came out interesting... I didn't like it at first because it reflected the light in an odd way, creating a blotchy effect in direct sun. But after a while it grew on me... and it actually looks kind of neat. The wood is 3/4" birch and stained dark (also a departure from my preference of either light or non-existant stains) with a coating of spar varithane. I have to admit that I rushed the finishing; it could have been done much better but that would have required an additional day or two.
The secondary is from Protostar and the focuser, cell, and spider are from University Optics. The UO parts are inexpensive, but prove the old saying that you get what you pay for. I like their solid rack and pinion focuser (perfect for an 11 year old), but am less impressed with their spiders and cells.
The optics tested out quite nice and the visual results are excellent. I'm pretty sure that the mirror is better than my 10" (which means it's time to get started on the 14" project). The goal was to get it done before SSP so that we could each have a scope.... so you can guess what I was doing over the July 4th weekend.
I did a quick check tonight that stars came to a proper focus, midway through the focuser's travel (without the barrel sticking into the tube), and that they appeared as pinpoints. The diffraction rings looked good, and I was able to catch a very dim view of the ring nebula from my driveway in Oakland.... It'll sure be fun to check it out later this week under much darker skies....