Re: What Does Image Rotation Look Like?

Chris L Peterson wrote:
On Sun, 7 Oct 2007 23:24:26 +0200, "Carsten A. Arnholm"
<arnholm@xxxxxxxxxx> wrote:

What prevents the off axis guider to track on a star in the field of
view of the imager? Isn't that just a question of how the off axis
guider prism is oriented?

The prism is always outside the bundle of rays that hit the imager.
Otherwise, it would cast a shadow. So you can't pick off light from a
star that you are also imaging.

That is now logical :-) Thanks.

With a
separate guidescope, the guide star may or may not lie in the field
being imaged.

True. In my case the two are aligned. It makes things easy.

They are aligned in my case as well. But the guider has a FOV several
times larger than the imager, so I may still choose a guide star that
is outside the field of the imager. The single most important factor
in guiding quality is S/N, so the brighter the guide star the better.
If my brightest star is outside the imager's FOV, that's the one I
normally pick.

I use a modified webcam for guiding and that makes it possible to guide on
quite faint stars, especially since I also have a short focal length
guidescope providing a fairly large guider FOV. The main problem is flexure.

Thanks for the good answers :-)

--
Carsten A. Arnholm
http://arnholm.org/
N59.776 E10.457


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