JimBuchanan wrote:
The way to avoid the equitorial mount, and use a simple tripod, is to take a 10 or 20 or 100 for that matter frame series at limited shutter speeds versus one long exposure. Then feed the files into a "stacking" program, which produces a composite with much greater signal to noise ratio. Yahoo groups has a DSLR astro group with all the answers.
The relative short focal ratios of camera lenses, say up to 90mm, compared to a refractor, and certainly the long focal length cassegrains, allow the avoidance of an equatorial mount and all its complications. If one is interested in star fields, where constellations are recognizable, 28mm thru 90mm lenses would be adequate and the above procedure takes advantage of the high sensitivity digital sensors, where the frames can be added or stacked to produce a higher signal to noise ratio image of short shutter speed frames. The earth moves, but at a short exposure of less than 60 seconds with a relative wide angle field of view, you will not see star trails.
I think the Leica APO 90mm would really perform well in this application. Whether it gave the field one is looking for is a personal thing. Extending the stacking of frames idea, wider fields can be built by stitching...
Really, if you aren't taking photos of planets, nebulas, etc, with high magnification optics, stay away from the equitorial mounts.
