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Posts Made By: Alan French

May 4, 2004 01:47 AM Forum: Equipment Talk

Protostar 3 vane versus curved spider

Posted By Alan French
Dave,

My first serious telescope was an 8" f/8, and it gave me some fabulous views of the Moon and planets (and deep sky) over the years. It had a traditional 4 vane spider with thicker vanes than Protostar uses. I suspect you would do just fine with either choice. I note that a friend of mine, who has been doing this as long as I have but has probably tried more Newtonian variations, opted for a curved spider in his latest creation.

Clear skies, Alan

May 8, 2004 02:14 AM Forum: Telescope Making

Optimum 8" f 8 Newt?

Posted By Alan French
A nice, smooth mirror puts you 80 percent there. Keep the secondary down to 20 percent or so, make sure it cools down well, put it on an equatorial platform or mount, and you'll be all set. Oh, you could move to the Florida Keys too - that would help quite a bit .

Clear skies, Alan

May 20, 2004 01:44 AM Forum: Telescope Making

Mirror Scratches

Posted By Alan French
Sam,

They will not change how the mirror performs. Chances are if you do go back, you will wind up with a few scratches or sleeks on the mirror anyway, and it could be a never ending battle. Worry more about getting a very smooth, well corrected figure.

And can you say "dust?"

Clear skies, Alan

June 1, 2004 10:41 PM Forum: Telescope Making

Ricks article on Coma

Posted By Alan French
Coma is an inherent property of a paraboloidal mirror. If the optics are properly lined up, coma is symmetrical about the center of the field. If things are not properly lined up, it is asymmetrical. If they are not too far off, somewhere in the field is the coma free region of the mirror.

In many cases, astigmatism in the eyepiece overwhelms the coma, and often it is this that amateur notices. Once the optics are misaligned, the center of the eyepiece and region of best performance no longer matches the coma free region of the field, so things may not look very good anywhere in the field. It depends on how badly the telescope's optics are misaligned and how wide a field the eyepiece covers without significant aberration.

Clear skies, Alan

June 14, 2004 11:11 PM Forum: Telescope Making

Refractor Problems...what have I done?

Posted By Alan French
Here is a 6" f/8 Fraunhofer achromat. The 6" f/8 refractor seems quite popular, so I thought it might be of some interest.

Clear skies, Alan

July 10, 2004 11:25 PM Forum: Equipment Talk

zero-power finders

Posted By Alan French
The Telrad has a larger wondow than the Rigel, but the Rigel has a smaller footprint. I've got both, but would tend toward the Rigel for future projects.

A minor point - it is a one power or unit power finder. A true zero power finder would show the entire sky .

Clear skies, Alan

July 12, 2004 10:00 PM Forum: Equipment Talk

Best Laser collimation tool recomendations

Posted By Alan French
Be sure to look up the collimation articles by Nils Olof Carlin in Sky & Telescope, expecially the one on using a barlowed laser.

Clear skies, Alan

July 15, 2004 01:59 AM Forum: Telescope Making

Truss tube center of gravity.

Posted By Alan French
I wrote an equation in Mathcad 5.0 equating the two ends in terms of the unknown balance point. It involved weighing and measuring everything, but FIND nicely returned a value that turned out to be darn close to the actual balance point. The main question I wanted to answer before cutting the tube to length and splitting it into two pieces was whether it would work on an existing mount.

July 23, 2004 12:26 PM Forum: Astro-Physics

What to choose?

Posted By Alan French
The Traveler, I think, is the clear choice. The case is legal airline carryon size, and it gives both fine low power, wide field views, and probably the best lunar and planetary views you can get with a 105mm scope.

Clear skies, Alan

August 21, 2004 01:08 AM Forum: Equipment Talk

Looking for lowest profile 2" to 1.25" adapter

Posted By Alan French
Astrosystems has an adapter that lets you lower a 1.25" eyepiece 0.5 inches below the top of the drawtube.

http://www.astrosystems.biz/focm1.htm

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