RE: [Utah-astronomy] Celestron's New CGE Series
Isn't that about the cost of a 6-inch Astrophysics refractor? If I had the money, that's what I'd rather have. On the other hand, $6K would finance a nice climbing trip to the Himalayas... -----Original Message----- From: Joe Bauman [mailto:bau@desnews.com] Sent: Wednesday, March 05, 2003 9:28 AM To: utah-astronomy@mailman.xmission.com Subject: Re: [Utah-astronomy] Celestron's New CGE Series Great, I forgot my drooling bib! Now what'll I do! Let's have a discussion on this, everyone. If you had $6,100 (its cost including shipping to SLC) to do the best you could with astrophotography, what telescope would you invest in? The only drawback I see is that it's f/11. But what do you think? A URL that gets you right there is: http://www.optcorp.com/cart/ProductDetail.asp?PR_ProductID=1950 Best wishes, Joe Joe Bauman science & military reporter Deseret News bau@desnews.com (801) 237-2169 _______________________________________________ Utah-Astronomy mailing list Utah-Astronomy@mailman.xmission.com http://mailman.xmission.com/cgi-bin/mailman/listinfo/utah-astronomy
-----Original Message----- From: Joe Bauman [mailto:bau@desnews.com] Let's have a discussion on this, everyone. If you had $6,100 (its cost including shipping to SLC) to do the best you could with astrophotography, what telescope would you invest in? The only drawback I see is that it's f/11. But what do you think?
I'd invest the entire sum in the mount, tracking hardware, & imager, then build a lensless Schmidt camera for imaging. But even $6,100 falls far-short of the sum needed if you want a high-end CCD included in the package, and/or seperate autoguider. The computer's a given, right? If we assume that we'll stick with 35mm emulsion-based photography, already have the camera & adapters, and just want to spend the money on a scope-mount package, then there are dozens of commercial offerings that are all about on the same level. Just avoid a fork mount if you're really serious about imaging with a portable telescope. Go with the largest aperture you can fit in the budget and still fulfill your imaging criteria. C. __________________________________________________ Do you Yahoo!? Yahoo! Tax Center - forms, calculators, tips, more http://taxes.yahoo.com/
Chuck, Very interesting. Tell us more about then building a lensless Schmidt camera for imaging -- how hard that is, what it would cost, etc. Also for those of us who aren't sure, is that like a reflector with the chip or film in place of the eyepiece? Thanks, Joe Joe Bauman science & military reporter Deseret News bau@desnews.com (801) 237-2169
Joe, a lensless Schmidt is basically just a mirror of fast f-ratio, with a diaphragm located at the radius of curvature and a film holder or imager at the prime focus. Coulter Optical sold a kit for many years, of a 5" lensless Schmidt. There was a construction article in S&T about 25 years ago. Very simple, the author used balsa sticks to support his carboard diaphragm. His B&W photos of deep-sky objects taken with it were some of the best taken by an amateur at the time. The imager can be either a film holder for conventional photography, or a CCD. It occupies the same location as the secondary mirror in a SCT. Production SCT's place the corrector at the approximate focus of the primary mirror. For best performance, the corrector should be placed at the radius (2x focus) but this would result in a telescope that's twice as long, reducing much of the appeal of the design from the consumer's point of view. A lensless Schmidt avoids the corrector completely. The penalty is that the mirror must be appreciably larger than the diaphragm- Coulter used an 8" mirror for a 5" clear aperture camera. But the resulting imagery is excellent. Biggest drawback of a Schmidt camera of either type is the location of the image plane. It's inside the optical tube, so films must be replaced after each exposure. A CCD would eliminate that problem. Celestron's "Fastar" system is basically a SCT that converts into a Schmidt camera by replacing the secondary mirror with a CCD. You could build a lensless Schmidt for only the cost of a mirror blank, grinding/polishing supplies, and aluminizing cost. Everything else can be scrounged at little to no cost. The fast curve could be tricky to figure, but very possible. C. --- Joe Bauman <bau@desnews.com> wrote:
Chuck, Very interesting. Tell us more about then building a lensless Schmidt camera for imaging -- how hard that is, what it would cost, etc. Also for those of us who aren't sure, is that like a reflector with the chip or film in place of the eyepiece? Thanks, Joe
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participants (3)
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Chuck Hards -
Joe Bauman -
Kim Hyatt