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LBN 576 - The Garlic Nebula

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Posts Made By: Alan French

August 27, 2003 12:03 PM Forum: Equipment Talk

cleaning question...

Posted By Alan French
Generally mirror cleaning -

Put mirror in sink on thick towel. Pour diluted detergent onto mirror and let sit. Rinse thoroughly with tap water. Rinse with distilled water. Rinse with isopropyl alcohol. If there are remaining spots, try rinsing them off with acetone. The stuff from a hardware store is fine, but, if you worry, got it from a pharmacy. If you stand your mirror on edge, most of the water will slid off a clean mirror. Remaining spots can be removed with the edges of small pieces of paper towel.

If you slug spot does not come off, use spit on it. Saliva can remove stuff untouched by other solvents. After that, follow the above procedure.

I often find I can skip the alchohol and acetone.

If you use soft corron balls, old undershirts, or such to gently rub the mirror, even under water, you are almost certain to get fine scratches. All it takes is on piece of grit on the mirror. If such cleaning is required, I give optics one pass with a Kleenex that was wet with a mild detergent solution.

September 20, 2003 01:03 PM Forum: Equipment Talk

10" plus SCT for Planets?

Posted By Alan French
Gregg,

A 10" or larger SCT should certainly do better than a 6" f/8 achromat, expecially under southern Florida skies (lucky you). You might give some thought to a 10" or larger quality Newt too, on a equatorial mount or equatorial platform if at all possible.

Actually, I'd rummage around and see if you can find some local amateurs with similar scopes you can look through. IMHO, no one should buy a telescope without seeing an example under the sky first.

Clear skies, Alan

September 20, 2003 01:05 PM Forum: Telescope Making

Double scopes

Posted By Alan French
Robert,

That's not supersized. A binocular 20" Newt Dob, that's supersized, and has been done nicely. I had the chance to use one many years ago at Texas Star Party.

Clear skies, Alan

September 22, 2003 11:55 PM Forum: Equipment Talk

Building a mount - Engineering Questions?

Posted By Alan French
The article by Russell W. Porter of long ago in Amateur Telescope Making (Book I) is well worth digging up. Don't, however, pay attention to the idea that a solid mount has to be massive.

September 23, 2003 01:48 AM Forum: Telescope Making

scratch on primary mirror

Posted By Alan French
No, a small scratch will not effect the mirror's performance. Even a few small scratches would not be an issue.

September 26, 2003 10:08 PM Forum: Refractors

Collimating a refractor?

Posted By Alan French
A Cheshire works very well. I set the scope out on a bright sunny day. Cover the lens and place the Cheshire directly in the focuser with the angled reflector aimed toward the bright blue sky. All the reflections you see when you look through the Cheshire should be concentric. Because most modern quality refractors are well corrected for coma and astigmatism over a fairly wide field, further tweeking in not needed.

September 29, 2003 10:19 PM Forum: Refractors

Re: AP 130 vs TV 102--not a sure bet!

Posted By Alan French
David,

If you are talking about relatively large exit pupils, I would agree. However, you also get into problems with very small exit pupils, but in this case the larger scope is helpful. Most older folks start seeing floaters and other junk when the exit pupil gets down to 1mm or less. At equivalent powers, a larger scope gives a larger exit pupil, and this can be a real benefit for us older folks. Of course, the difference between a 5.1" and a 4" scope is not very great in either situation.

Clear skies, Alan

October 4, 2003 11:07 PM Forum: Equipment Talk

gregorian/cassegrain

Posted By Alan French
I suspect your are talking about two different Cass scopes. A traditional Cass has a convex secondary, which is mounted inside the focal plane of the primary mirror. A Gregrian has a concave secondary, which is mounted outside the focal plane of the primary. A Gregorian secondary is somewhat easier to make, at the expense of a longer tube. A Gregorian gives an erect image.

October 11, 2003 11:51 PM Forum: TeleVue

TV 40mm Wide Field

Posted By Alan French
It was discontinued some time ago. It has a 41.2mm field stop.

Clear skies, Alan

October 12, 2003 02:46 AM Forum: Equipment Talk

Center spotting primary

Posted By Alan French
I use a router table to make an 1/8" plexiglass circle exactly the same diameter as the mirror face. I make a 1/4" hole in the center of the rough cut disk to turn it true. I slide the shank end of a 1/4" bit - perhaps with a little tape around it to make a snug fit - so about 1/8" protrudes. Then I place a fiber or hard rubber washer on the protruding shank and dab a little bit of rubber cement on it. The disk is then carefully centered on the mirror, and a little pressure flexes it and pushes to washer against the mirror. While holding it, I pull out the drill. If you need a bit more clearance in the center for your mirror put a few bottons of double sided foam tape around the edges (leave the paper on the side toward the mirror!).

The plexiglass also makes a nice cover for storing or shipping the mirror.

Clear skies, Alan

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