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Old 16-11-2017, 05:00 PM
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ChrisV (Chris)
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Polar aligning CGEM

A few questions about polar aligning.

How good does my polar alignment have to for good guiding? I know its probably an open ended question and depends on my mount/scope/camera. If this helps, I'm using an ASI071 with a 472mm FL refractor (2.1 arcsec/pix) and a 1000mm FL newt (1.0 arcsec/pix). All on a CGEM. At present my guiding accuracy range from 0.7"rms on a good night to 1.2-1.5"rms on a not so good night (this occurs more frequently).

I'm finding it hard to get it to within 2min. Is that good enough?
Also, I find polar aligning it a bit clunky.
- The ALT isn't too bad. But its hard to get good resolution as it shudders a bit with small moves. So the smallest I can reliably move is ~0.5'.
- The AZ is worse. It really clunks along as its moving one rough anodized (or just painted I'm not sure) surface over another. So when I move the AZ it also greatly affects the ALT. Maybe I should take off the surface and polish it? Any other things people do?

Last edited by ChrisV; 17-11-2017 at 08:07 AM.
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Old 16-11-2017, 06:02 PM
kens (Ken)
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Generally speaking, 5 arcmin or better is pretty good. You can enter values into the calculator at
For instance inputting an alignment error of 5 arcmin, FL 1000mm, Guide star angle 0.5 degrees, declination 80 degrees and exposure time of 5 minutes yields a field rotation of 1.6 microns which is much less than a pixel on most cameras.
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Old 17-11-2017, 09:36 AM
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graham.hobart (Graham stevens)

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polar align cgem

on my old cgem I put a thin Teflon disc under the mount head where it bots on to the tripod- it made adjustments smoother. I suppose any lubrication will do
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Old 17-11-2017, 11:07 PM
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ChrisV (Chris)
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Thanks all.
Great idea. I'll try the teflon.
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