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Posts Made By: Ed Jones

March 22, 2005 01:18 PM Forum: Equipment Talk

Curved Spiders

Posted By Ed Jones
For what it's worth diffraction analysis in Zemax doesn't show any improvement in the diffraction disk using curved spiders.

Ed Jones

May 23, 2005 12:33 AM Forum: Telescope Making

Tile Tools for mirror grinding

Posted By Ed Jones
Robert, If you have already roughed out the curve you can use zinc pennies instead of tile on your plaster back. They make a great scratch free lap and are probably cheaper to boot. Ed Jones

May 25, 2005 12:56 PM Forum: Telescope Making

Star test aberration

Posted By Ed Jones
Michael,
Changing the mirror BFL from design does introduce spherical but it depends on how much you're off by. If you are 2 inches off then you will see .046 waves of spherical, not likely what you are seeing. A miss of 4 inches will give you .092 waves which could. Are you overcorrected or undercorrected?

Ed Jones

June 15, 2005 12:31 PM Forum: Equipment Talk

One For Roland Christen

Posted By Ed Jones
If you think your scope will hold its alignment looking down you could try autocollimation against an oil flat.

Ed Jones

July 19, 2005 09:52 PM Forum: Telescope Making

cylindrical mirrors

Posted By Ed Jones
Jess,
I've made a number of glass spherical cylindrical lenses in the 6 to 7 inch size with fairly long radii. I think the idea is with all respect Sheer Lunacy. If you think parabolizing is hard try multiplying that difficulty by 10 to the second or third power.

Ed Jones

August 20, 2005 06:34 PM Forum: Telescope Making

Testing optical flats redux

Posted By Ed Jones
You could use the Raleigh water test with a colored dye in the water but you need a colimating lens for this test. See July 1990 Sky & Tel.

Ed Jones

June 6, 2006 11:39 PM Forum: Solar System Observing

Projection Solar Viewing

Posted By Ed Jones
Here's the simplest and best solar projector bar none. It mount on a camera tripod and projects a 8.5 inch solar image.

Ed Jones

February 1, 2007 12:49 AM Forum: Telescope Making

Hershel's Telescope Making

Posted By Ed Jones
One thing that has always puzzled me is that Herschel did most of his observing with a 18.7 inch of 20 ft focal length. That is only f/12.8. I don't know at what angle the mirror was tilted (I don't think he actually observed on axis with his head in the way). If the tilt was about 1.4 degrees giving 2.3 inches clearance with the incoming light the resultant image is quite horrible if it was a figure of revolution.(pic) So how was he able to see so much planetary detail and split close doubles that other observers couldn't with such an image? Did he polish an off axis parabola?

Ed Jones

February 26, 2007 05:48 PM Forum: Reflectors

Off-Axis Reflector Astigmatism

Posted By Ed Jones
If you have a simple laser collimator you can check that the laser hits the center of the mirror (I'm assuming that the eyepiece focuser is square to the mirror and not the original parabola). If that's OK then ajustment of the primary should find a position where the image is perfect. That position should be where the beam exits at a distance equal to the distance of the center of the mirror to the center of the original parabola. If there is no position where the image is perfect then the mirror might have been warped when it was perforated.

Ed Jones

March 6, 2007 06:20 PM Forum: Reflectors

Off-Axis Reflector Astigmatism

Posted By Ed Jones
The way I read their instructions is that the focuser is aimed at the center of the primary mirror center dot. Hence a laser should hit the center dot of the primary but it won't return to the focuser.

Ed Jones

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