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Re: LX90 Or LX200

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Posted by Daniel Johnson on February 6, 2003 04:46:27 UTC

First, about the microfocuser: For visual observations it’s not necessary. For photography it is a great plus—this includes digital photography through the eyepiece of planets, though you can get by without it for such digital snapshots.
Second, about your concerns that you won’t be good at astrophotography and will give it up: there are many levels of the hobby, some ridiculously easy, and some challenging. The ridiculously easy: Use your scope (on a polar wedge) as the platform for piggybacking an ordinary camera with ordinary lenses. On my office wall I have photos of the Milky Way in Sagittarius taken through ordinary 50mm focal length lenses, not through the scope itself, and my customers stare at them in wonder. You don’t even have to guide if your polar alignment is halfway good. Even for 135mm lenses, if your piggyback attachment to the main scope is solid, little guiding is necessary. When you start this way, the gratification of easy success will give you the fortitude to continue to harder methods, and your non-astronomy friends will think you’re a genius.
Those harder methods include photographing at f/6.3 (with the focal reducer) through the scope itself (hardest, VERY hard at first), or through a short-focus piggybacked on the scope (less hard but still a challenge for a typical 80mm aperture f/6 scope. I’ve been pleased with my Megrez 80mm by William Optics for this. It is a medium-quality refractor. One does have to use the “minus violet” 2-inch filter to eliminate violet halos around bright stars with this and most non-apochromatic refractors). Using the refractor allows photography of larger objects such as the Andromeda Galaxy which simply won’t fit into the photographic frame of an 8-inch scope.
The LX-90 is a good buy for purely visual work, and it can be made to serve for photography, according to the Sky & Telescope review. But it is simply not MADE for photography the way the LX200 is, and it will always require lots of visual guiding. Autoguiders are not an option with the LX90, I understand. I love my 10-inch LX200.
As for the extras for photography: for digital snapshots, you need a digital camera and something like the Digi-T system from Scopetronix.com . For film, you need the 35mm camera, dovetail rails for the top and for the bottom of the scope, rings to hold your guide scope to the top rail, the guide scope (or refractor to be used for photography), an illuminated reticle guiding eyepiece, counterweights for the bottom rail, and the wedge. You can’t do astrophotography (except for snapshots) in altazimuth mode on the LX90, and the “field derotator” option for the LX200 is inferior to a wedge.
Finally, how clear is the space station? Usually not more than a moving blur, though in moments of brief clarity amateurs have taken s few sharp photos of it. The current technology in professional observatories called “adaptive optics” was in fact developed by the Department of Defense to allow sharp pictures to be made of enemy satellites, since the atmosphere usually blurred such photos. The observatory in effect changes the shape of its mirror (or a smaller mirror in the light path) many times per second to counteract atmospheric blur. You won’t have that option.
Hope this helps.
--Dan Johnson

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