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Posted by Daniel Johnson on November 14, 2003 04:51:39 UTC

Although I own an ETX-90 myself, I seldom use it, since I own several larger scopes. I do use it to show a few things to groups of school children, or when I want to go on a trip and can't take my larger scopes. Aperture makes a difference, though the difference between the smalles Orion Dobsonian scope (4.25 inches, about 108mm) and the ETX-90 is not much. The ETX can also be used for daytime viewing, giving upright images, rather than the oddly tilted or upside-down images of a Dobsonian. For astronomical objects, such a tilt of the image is irrelevant, since there is no true "up" direction in space.
On the other hand, if you can possibly afford the 6-inch Dobsonian, the step up in aperture (150mm) gives striking improvements compared with the ETX-90. When I first entered astronomy about 30 years ago, a 6-inch scope was more or less the standard scope that serious amateurs first purchased, once they tired of the "Christmas trash" department store scopes. Nowadays, improved production techniques make it possible for many amateurs to buy much larger scopes, but 6 inches is still a very, very nice beginning scope.
I don't have strong feelings one way or the other regarding the ETX-90 and the Orion 4.25-inch Dob; both are decent, but they'll leave you hungry for more aperture. (Then again, my 10 and 12.5-inch scopes leave me hungry for more. This is a disease, and the cure is always another scope...). Either of these two scopes is much better than department-store scopes of similar price, even though you get computerized gizmos with some of the department-store scopes. There is no free lunch. The price of the computer has to be taken out of something else, so that means lower-quality optics. If you want both the computer and the good optics, it costs more. The 6-inch Orion Dob can have a computer added later if you want. The smaller Dob and the cheapest ETX cannot, but I lived for decades with no computerized scope, and life was good anyway.

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