Thread: Guiding woes
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Old 29-03-2012, 06:02 PM
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gregbradley
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Join Date: Feb 2006
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If stars are triangular it sounds like you have coma as well.

So you need to differentiate between coma and guide errors. Guide errors are in the same direction across the whole image usually,(sometimes they can rotate if your Polar Alignment is badly off).

Coma is comet shaped stars usually worse off centre and in the corners.

Also tilt will give out of focus stars in one side or corner of the image. If your scope has a corrector then tilt could also cause coma like effects.

Also your corrector (if using one) may have a metal back distance and you are not close to it causing coma.

If polar alignment was off and you got an improvement I suggest a brand new T-point model (delete the old one) and after say 50 point model read the polar alignment report and adjust the mount.

Have you done PEC yet?

I wonder if the PMX PEC software is bugged. Chris had a lot of trouble with his and PEC made errors worse. I did a standard PEC curve and I am not convinced it is improving guiding performance also. I get the same or better results with PEC turned off. Also the curve I made and what was saved in the mount seem different.

Chris used Pempro and got a great result.

I have used Precision PEC on my PME and it definitely helps get round stars.

Greg.
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