Barney: If a telescope is used in alt-azimuth mode, such as a Dobsonian or a fork with no wedge (fork pointed straight-up), the field will rotate as an object is followed. Imagine the telescope facing east; an up and down motion in altitude corresponds to east-west motion on the sky. Now face the scope south, and see how an up and down motion corresponds to north-south on the sky. In the six hours from when an object rises until it crosses the meridian, the field has rotated 90-degrees. A de-rotator compensates for this, rotating the camera one revolution per 24 hrs. Equatorially mounted scopes, like Dobs on platforms or fork-mounted SCT's with wedges, do not have field rotation. C. --- "Barney B." <aaah@sisna.com> wrote:
Brent said: Unless you are going to use an image de-rotator, you'll need to have an equatorial mount.
What is a de-rotator? How does it work on a fork mount?
Barney
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