Posts Made By: Thomas Dey

Cool! About 15 years ago we had a swarm of 5000-10000 set up a hive in our chimney, completely clogging it for about 3 feet down. I went up on a cool, rainy night and killed them with 2 cans of hornet spray. It's of course the single Queen that causes the monolithic swarm. All they are doing is seeking a new place to establish a new hive. Thanx for sharing the story.

Here is something similar that is newer and has lots more stuff with it. http://www.astromart.com/classifieds/details.asp?classified_id=924322 Value is always debatable. I would personally offer no more than half. For better or worse, older mid-sized dobs seem to sell cheap. Nearly all the worth is in the quality of the optics. And that can best be determined by using it. Many older commercial dobs are disappointing in that regard. Tom

That looks nice and I especially like that one picture pretty much shows Everything regarding how you designed and built it. This is 1st time I've seen this project; couple questions: It's a classical Cass? Does a spider or stalk hold the flat folding mirror? What's the F# and lowest mag you can use? Do the PM and SM need baffles? How is the performance? Nice job! Thanks for sharing. PS I’m on a writers’ site as well and believe many/most hobby sites seem to have had their glory days like ten years ago. Maybe Twitter, Facebook, etc. have inexorably changed the favorite ways that people communicate?! … sigh … Tom Dey

OHhhh... I just had a Gestalt here... That is LITERALLY optics stripped from a C-14? Tom

Hi Ed, I used to do coatings for a big commercial place. A baffle would generally need to be removed for at least three reasons: tooling, shadowing and contamination: most tooling precludes "sticking out" things, the baffle would likely shadow the mirror from the coating source and most anything other than glass or metal can contaminate the vacuum chamber. There is a (typically dark red) RTV "potting" material that is used to attach things to optics. It is used because (properly applied) it will not stress optics, is vacuum-compatible and long-lasting (mil-spec cert for satellites, etc.) The RTV "Adhesive Sealant" that you can find in the hardware store works well. The kind that smells like acetic acid is the good stuff e.g. GE. That's not the same as the potting, which is pumped or gravity-fed in, but is more convenient for home use.

No...but: I did testing all my career and can at least ID the best test configuration for biggish mirrors. If at all possible, the best (most meaningful) test is pointing upward in autocollimation off a downward-pointing precision calibrated optical flat. This is usually called a "test tower." It is of course wonderful for testing complete telescopes (OTAs) but also great for plain vanilla paraboloidal mirrors. For that, a perforated plano with the parab focus in the hole is ideal. That way the interferometer sees the parab twice, in all its magnificence. Nother good (necessary) practice is that the cavity be properly calibrated and backed out, so what you get in the report is your mirror only, without any artifact of the test itself. Ummm... and of course the mirror on its whiffle tree support and well-thermalized to ambient. Under those circumstances, a characterization accurate to 0.005 wave surface vis RMS is likely. I would be a bit skeptical of "Ronchi Only" fringe patterns. Those fringes can look decent because they are most often (even necessarily) highly desensitized. That because the nature of Ronchi is that it shears the wavefront to get fringes. So the fringes are mapping lateral wavefront slope, NOT the raw wavefront itself. You can immediately tell how desensitized it is because the image of the mirror looks sheared like two circles laterally displaced. that displacement relative to the circle diam is also the desensitization. If e.g. 10%, then the fringes you see will look 10X "better" than if regular laser interferometry had been done. This is probably "too much info" sorry for that. Oh yeah, I actually had a 24-inch test tower in my barn years ago! Tom

Hi Nancy, I donated a very expensive scope to a school about 40 years (?) ago. My Tax Lady told me to get a professional appraisal. There was one locally who specialized in industrial equipment and he researched it. He also needed to look at the stuff. I got audited but was fine.

Hi Rod, thanx for the link, interesting and rather encouraging. "The lights may be just as bright, but not as white." So they're cetainly not even approaching IDA's standards, but at least headed in the right direction and some level of awareness. Now if only municipalities, EPA, etc. would seriously address Light Pollution in all it's negative effects. I especially like (even love) LPS (low-pressure sodium) street lights. If ALL outdoor lighting were minimalist LPS cut-off... Ref U.S. Patents #4161014 and #4161015... sigh Tom

Very cool... It looks especially good with averted vision! Tom

Hi Frank, that's a bummer. My left (dominant) is acting up with an IMMENSE opaque floater. 90% of the time it blocks most all of my central vision. They may be able to extract it doing a "vitrectomy" which has risks. Most all scopes are one-eyed, so the impact on the hobby shouldn't be debilitating. I sometimes worry over things like, "What if I'm driving and get a mote in my one good eye?" And I have mostly binos...

I've enjoyed Dobs from tiny to gargantuan. There is no right answer. I do remember thoroughly enjoying my home made 6-inch for a couple of years and was then comfortable, experienced and ready to go bigger. You could of course forgo the goto and even the encoders to get used to finding things "the old fashioned way" which does have value. Having a decent low power eyepiece and then USING it a lot will be the best value of all.