Basically, it's a drawtube that rotates, driven by a stepper motor via belts or gears. Whatever's locked in the drawtube is rotated with it. They don't need active control, since they are basically just a clockwork mechanism, 1 rpd., but it wouldn't surprise me if they existed with programmable rates or scripting capability. There are commercially-made units; I think even Meade offers one for their 16" SCT when it's mounted in alt-az. mode. But I don't have the details for any off-the-shelf units. C. --- "Barney B." <aaah@sisna.com> wrote:
Hi Chuck. Thanks.
I understand field rotation but what is a de-rotator? Is it something that can be bought in a store? How would it work? Would it install between the camera and the scope? What controls it? Who makes one?
----- Original Message ----- From: "Chuck Hards" <chuckhards@yahoo.com> To: <utah-astronomy@mailman.xmission.com> Sent: Saturday, March 01, 2003 3:39 PM Subject: Re: [Utah-astronomy] de-rotator
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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