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Re: 8" EQ's - Celestron Vs. Apogee (also Orion)

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Posted by Adam E. on February 26, 2000 20:24:15 UTC

: : I'm looking @ a Celestron G-8n (f/10)for $699.00 vs. an Apogee 8" Newt.(f/4)with motor drive and hand controller for $100.00 less. Why? Being new to all this, I would assume it has something to with the focal ratio, or is the Apogee just poor quality? Could someone explain to me in simple terms what focal length is, and it's importance when comparing scopes? : : Thanks!

: : About the Celestron Gn8 and the Apogee-- The Celestron is on a heavier mount, which is a Chinese-made knock off of the Vixen Great Polaris (and probably not as good IMHO). The Apogee is on a much lighter mount.

: The Celestron 8" F5 tube has a glass element at the focuser (I think) which is supposed to serve as a coma corrector/field flattener. I also suspect that it does a bit more (later).

: The Apogee tube appears to be the same unit sold under many other names, all for about the same price. It is made in Taiwan. How good is it? I dunno. Consider that the Vixen 8" F4 optical tube, which is very well made, sells for roughly $1000--without the mount!

: Which brings me back to the Celestron. You get the tube and mount for less than $700. Remember that coma corrector/field flattener? I suspect it also corrects for a spherical mirror. A spherical mirror is MUCH cheaper to make than a paraboloidal mirror, and if this is the case, you should consider that there are limits to what the corrector can do in addition to its other duties. Celestron may clarify this.

: I hope this is not too late to be of help.

: I have been in the market for an 8" reflector myself. Here's what I have learned about the G-8N and a different alternative, the Orion Skyview 8" EQ. The primary mirrors in both are parabolic, and the corrective optics are in the tube in front of the elliptical mirror (it sounds like it is just one lens). The G-8N uses 4 vanes, the Orion uses three. A user of a G-8N told me that the crosses in the Airy circles were irritating, though I suppose this is a matter of taste.

: The Orion has a shorter tube and is still faster (f/5 vs. f/4), not a great thing for planets, I suppose. An Orion salesperson told me that the EQ mount for the Orion scope was at its limit (not a good sign), but that the Celestron G-8 (a SC) is not overmatched for its mount, the CG-5. This is the same mount used for the G-8N, and as the tube weighs about the same as the G-8, my guess is that the CG-5 mount is quite a bit sturdier than the Orion version.

: Based on what I have learned, the best options in a reflector with an EQ mount are 4.5-6" models that avoid corrective optics (e.g., Celestron 150HD or Orion Skyview 6), or (better) a 8-10" Dobsonian. For a little more than the cost of the Celestron G-8N, you can get a Meade LDX500, a CS on an EQ mount, which would get you superior optics for planets at the cost of field-of-view.

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