Posts Made By: Alex McConahay

Larry,

I don't know that scope in particular, but our club, the Riverside Astronomical Society has a lot of pretty crafty people in it, and if you met up with us some weekend at a Star Party, we could probably help. See rivastro.org.

Alex

Steve,

Many amateurs leave their telescopes in unheated (and uncooled) garages. However, If I were in Chicago (and I have been many times--sometimes it is humid there), I might rethink covering in tight plastic. And watch out bringing it in from the very cold outside to the moderately cold garage. If you got condensation, and then completely air-sealed the scope, you could trap a bunch of moisture inside that tube. Who knows what may take up residence on your optics?

Alex

Stuart,

Your local auto upholstery supply store (there is one in the nearest big town) will have waterproof pasteboard, and various plastic materials that will do the job. There is a vinyl/foam combination material that holds its shape, but can be form fitted. Sorry, I do not know what it is called, but you will find it if you spend a few minutes wandering through the store.

Alex

Dan,

I agree with your main point--Galileo was not in real trouble for believing, or even writing that the earth went around the sun. He got in trouble for making the pope a simpleton in his book. THe pope's view was represented as "Simplicio," the simpleton characer.

Galileo was in many ways like the bright, young, energetic new kid at work that has a bunch of good ideas, but calls the boss an idiot for not accepting them and making him a hero. THe boss gotta do something, even if the ideas are good. So he fires the young idea boy.

Galileo went on for a long time believing and teaching the heliocentric theory. He only got arrested after he called the pope a simpleton.

Alex

For anybody truly interested in this topic, one of our members has done a lot of research and will be presenting his experience and advice at the Riverside Astronomical Society meeting at La Sierra University, Riverside, California, this Saturday night, December 14, 7:30 p.m. See Rivastro.org for details.

Alex

Dave,

It looks like nobody has answered your question.

A field stop is a circular disk, with a circular hole in the middle. It sits on the field end of an eyepiece (towards the objective, and away from the eye). Light from the objective comes through the circular hole. All other light from the field end of the scope is stopped. Basically, it marks the outer edge of where light is allowed to come through the piece of glass.

On most eyepieces, you can see the field stop by looking from the field end of the eyepeice. It is the blackened disk. ON some eyepieces, however, the "field stop" is actually buried on the far side of some of the glass.

And yes, different eyepeices have different locations for the fieldstop.

Imagine a lens that is very sharp in the middle, but progressively less sharp as you move to the edge. (All lenses, no matter who makes them and whose name is on them, have this problem.) At some point, you find the sharpness at the edge is just unacceptable. That (or better yet, just before that) is where the designer puts the "Field stop" to keep any rays from further out getting into the view.

If you have a 60 degree eyepiece, you may be able to increase its apparent field of view by taking out the field stop--but this would result in an unacceptable edge. THis is a technique employed by some manufacturers. That is why you can take a 55 mm plossl, remove or enlarge the field stop, and sell it as a "Wide Angle 68 degree.) It does in fact have a wider field of view, but the extra 13 degrees (or so) are pretty ugly.

Alex

Steve,

Get yourself at least one goto scope on a driven mount. A big ETX will do, although there are others. Optical quality is not critical. Put a one power viewer on it and use it as your "Finder Scope."

Get yourself as many six inch Dobs as you can find, maybe eight inchers if you have good skies. Make sure they have matching one power finders. Your students can use the goto scope to "find" the object, and then match their own one-power finders to wherever the goto is pointing. Much easier than using a star chart alone.

Alex

David,

I use a 22 Pan with a shorty Barlow and a Powermate, both 1.25. You gotta remember that the 22Pan and similarly mounted Televue eyepieces are really 1.25 eyepieces. THe 2 inch part of the 1.25/2 barrel is for convenience and has no real optical effect (except shifting where the eyepiece focuses, depending on focuser).

Alex

Mark,

Actually, it is not as if the dovetail rail just touches at one or two tangent points. I think you will find those dovetails attached to radius blocks, or something that has the same inside radius as the outside of the OTA. This spreads the work over a larger area. It is true, however, that you just have four #10 (I believe) screws just holding the whole thing together. The weak point in the arrangement, however, is where the dovetail meets the mount, in my opinion.

Actually, I don't think you have anything to worry about. The arrangement has worked for many SCT's.

Alex

If you really want to show off, point out that some parts of Australia are 18 hours off, some more and some less than 18, and parts are even a half hour off of that?

Alex