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Re: Scopes

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Posted by Robert May on July 10, 1999 04:35:37 UTC

I don't know if you have been lurking on the Sci.astro.amateur Newsgroup but they have repeatedly gone through discussions on refractor vs. reflector arguments. Before you get into refractors and thier own set of problems, May I suggest that you investigate the longer focal length newtonians. Most telescopes of the reflector designs don't work to thier capabilities because the scopes are not baffled to keep light out like refractors often are. You look into the tube of a refractor in the daytime and almost all the light you see is the light that is coming directly from the lens. When you look into the typical reflector, you see light coming in from all over the place. This light is why the contrast isn't as nice as with a refractor. As far as the quality of scope is concerned optically, I would prefer the reflector as there is no color abberations (which are unfortunatly a result of refraction through glass) to bother you usage of a camera. I don't know how many Celestrons or Meades you have seen but the quality of the run of the mill 8 or 10" is all over the place. You could be looking through an instrument that couldn't pass a 1 wave error test and may not be well collimated to boot. Before you settle down to a particular instrument, may I suggest that you go search the web (I don't remember where I saw it) for the procedures on baffling a telescope. I have seen 2 different websites out there that have treated the subject and I wish sometimes that I had bookmarked one of them. If I was to build an observatory, I would want the biggest apeture in it and a decently long focal length so I could use some decent eye relief EPs with it. I own the 200" refractor (focal length) and it makes for nice large views of about 40 arcmin. of diameter. The lens (4.25") is a singlet so I have plenty of chromatic errors with it. Because of a bit of baffling, it has nice high contrast views and I could tell the difference between before and after putting in the baffle - the background turned darker. The reason for apeture is that there's a lot of scopes out there that can show a mag 12 sky (about what you'll get with a 6" scope) and there's a lot more out there that can be seen with a 30" or larger scope. In other words, really make sure that you want a refractor before you go buy one. They're expensive in the bigger sizes and they don't work as well as a smaller refractor due to the color problems that afflict refractors.

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