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Posts Made By: Alan French

December 21, 2003 08:49 PM Forum: Equipment Talk

D&G

Posted By Alan French
D&G has a very good reputation. Give careful thought to how you are going to mount such a beast. Such a large and long ota is hard to mount well.

Clear skies, Alan

January 1, 2004 01:57 PM Forum: Telescope Making

Can an apo triplet be made from an achro doublet?

Posted By Alan French
Since a triplet requires careful selection of three glasses that, when combined, give very little secondary color, and have the proper radii to reduce other aberrations to unobtrusive levels, I suspect adding a third element to an achromat is pretty much out of the question.

You can add a corrector well removed from the main objective. The Chromacor has been mentioned, and is probably the best and easiest choice if you want to improve an existing achromat. Roland Christen detailed a sub-aperture "Tri-spaced" corrector many years ago in Sky & Telescope.

Clear skies, Alan

January 6, 2004 12:08 AM Forum: Telescope Making

Reflector focal length measurement

Posted By Alan French
You need to have it so the eyepiece's field stop, which defines the outside of the eyepieces focal plane, can be made to coincide with the focal plane of the mirror.

January 8, 2004 11:37 PM Forum: Equipment Talk

Wavefront error of an average C8??

Posted By Alan French
If this data was available, you should be concerned with the RMS wavefront error. PTV doesn't say very much about the overall quality of the mirror.

January 10, 2004 10:07 PM Forum: Equipment Talk

Oh Boy! Clear skies!

Posted By Alan French
It was -15 F here last night, and the only reason my wife didn't go out was because of the early moonrise. It never got above -1 F today, and is now -4 and windy. I have her 10" f/6 outside cooling down, and she will be out tonight for sure. Me, I'm staying in, although I suspect I will see how Saturn is when she is done with her deep sky "hit list" for tonight.

Clear skies, Alan

January 11, 2004 04:46 PM Forum: Equipment Talk

How many cheap scopes before......?

Posted By Alan French
My first scope was a Gilbert 40x reflector, which was a Christmas present. My second was a 60mm Unitron refractor, which, while not "cheap," was too small in aperture to hold much interest for the planetary views I desired. My third was a homemade 8" f/8 Newt, which kept me happy for many years. For an 8", the views left little to be desired.

Clear skies, Alan

March 6, 2004 02:16 AM Forum: Equipment Talk

Crazy Eyepiece Prices

Posted By Alan French
For a quality eyepiece....

Top quality glass, free of microbubbles.
Coatings matched to each glass type.
More thorough and time consuming polishing process.
Closer tolerances, and insistance on better surface quality.
Greater care to insure clean surfaces during assembly (not easy nor cheap to do).

Some possibilities that could explain the prices. As usual, no one forces anyone to buy these nor to consider them "good values," but the market seems to be there.

Clear skies, Alan

March 9, 2004 03:06 AM Forum: Equipment Talk

Tell me what you think?

Posted By Alan French
It seems quite fair, but I fail to understand why the buyer didn't try to clean the eyepiece. Eyepieces get stuff on them, and need to be cleaned from time to time. Even a quick squirt with a blower bulb might do the trick.

March 11, 2004 03:41 AM Forum: Refractors

Symmetry in Star Testing

Posted By Alan French
See
http://aberrator.astronomy.net/scopetest/html/news.html

I don't see a lot of symmetry in the white light images of the APOs, and notice a lot of comments about how they test in green light.

Clear skies, Alan

March 27, 2004 04:17 AM Forum: Equipment Talk

Small aperature refractors? I don't get it?

Posted By Alan French
Different folks have different perspectives, interests, and needs. I like lunar and planetary viewing, and for planetary viewing I'd be unhappy to be restricted to anything under 8". I do own a 90mm APO, though. It is quick to set up, provides wide field views that are not available through any 8" telescope, doubles as a birding/nature scope, and does a surprising job on some deep sky objects under dark skies. It's just a lot of fun to use, and to push to its limits.

There are a lot of things other folks do that I don't understand, but they are not me, and I am not going to worry about what drives them.

Clear skies, Alan

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