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Posts Made By: Doug Scobel

June 15, 2005 04:45 PM Forum: Telescope Making

I need a 10" f/6 scope built

Posted By Doug Scobel
Hey Floyd, please forgive me if you've already addressed this, but why don't you get a copy of Kriege and Berry's book and make it yourself?

Alternatively, if your target is the Mars opposition this fall, then why not throw together a Sonotube-based scope, which you should be able to knock off in a month or two, and worry about the "real thing" later?

Just a suggestion.

Doug

June 28, 2005 12:50 PM Forum: Telescope Making

just started pushing the glass

Posted By Doug Scobel
Marcin, are you working center-over-center or tangentially? This is the pattern one would expect to see if you're working tangentially. If you are, now is probably the time to begin working center-over-center. Use 1/3 - 1/2 diameter strokes until the curve reaches the edge and the sagitta is correct. When that happens, go to 1/3 strokes for a few wets to get the surfaces into decent contact before going to fine grinding. Longer strokes will likely give you a slightly hyperboloidal mirror and oblate spheroidal tool, so you want to get the two disks into reasonable contact before moving to a finer grit size. Once the surfaces are in decent contact (it won't be perfect with #80 grit), use the reflection test as others have described to determine the focal length and get it close before going to #120. Doesn't have to be exact, but it's more and more difficult to adjust the focal length as you go to finer and finer grits.

Keep us posted.

Doug

July 5, 2005 01:19 PM Forum: Solar System Observing

Solar Fireworks on July 4

Posted By Doug Scobel
Eastern limb

July 6, 2005 04:17 PM Forum: Deep Sky Observing

Most Disgusting Objects...

Posted By Doug Scobel
How about IC 405, AKA the Flaming Star Nebula. More like Flaming Idiot Nebula. Without pristine skies it's virtually invisible. I think Patrick Moore included it in his Caldwell list just to make sure no one ever completes it. What kind of masochist is he anyway? >sad

Thanks for the therapy session - I feel better now.

Doug

July 11, 2005 03:10 PM Forum: Solar System Observing

Recent Tempel Observations?

Posted By Doug Scobel
Jim, Tempel1 is an extremely difficult target right now, because it is so diffuse. I was just able to see it on the edge of visibility in my 13” from mag 6.0 skies Friday. Could not see it Saturday night in the same scope but only mag 5.8 skies.

Keep in mind that for extended objects integrated magnitude is meaningless, but surface brightness and sky darkness is everything.

Doug

July 19, 2005 08:00 PM Forum: Telescope Making

mirror re-coating

Posted By Doug Scobel
Spectrum, by all means.

Doug

July 20, 2005 06:43 PM Forum: After Dark

Re: Green Laser Pointers

Posted By Doug Scobel
Thanks for relating your experience, Jerry.

Despite their utility and usefulness as a tool, their use constitutes light pollution. Just what we need more of. sad

Doug

August 3, 2005 12:51 PM Forum: Solar System Observing

Sunspots 2005-08-02

Posted By Doug Scobel
Close-up of AR 792.

August 5, 2005 08:43 PM Forum: Equipment Talk

Pinholes in Coatings?

Posted By Doug Scobel
David,

I'm afraid your photo doesn't tell us a whole lot, since we can't tell how much of the surface you're showing us. How wide is the portion of the mirror in the photo, half an inch? Two inches?

Despite what others are saying, all coatings do not necessarily have pinholes. Pinholes I believe are the result of not pulling a high enough vacuum in the coating chamber. My 8" mirror done two years ago by Spectrum has no pinholes.

The best way to look for pinholes is to hold the mirror up with a strong light source behind it. Pinholes will be obvious. IMHO if your secondary mirror has more than say half a dozen pinholes then it doesn't have a very good coating.

Doug

August 10, 2005 09:21 PM Forum: Solar System Observing

Crescent moon 2005-07-08

Posted By Doug Scobel
Here's my best shot of the conjunction. Alas, Mercury is hidden in the clouds somewhere. I guess two out of three ain't bad.

Doug

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