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Guiding with PHD2 help for novice


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Hi, When performing drift alignment using PHD2, should the camera be mounted on the OTA or the guide scope? If the guide scope and OTA are not 100% perfectly aligned and the guide scope is used for drift alignment will that not ontroduce a significant error?


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I think that type of error would introduce field rotation which isn't going to be evident in the amount of time you drift align for.

Personally I rarely remove my camera from the OTA as that means retaking the flats.

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It goes on the guide scope as this is the thing that feeds back to PHD for the guiding (unless you are using OAG).  In essence the main imaging OTA and camera are along for the ride as the guiding is a closed circuit only with the guide camera/scope, PDH and the mount, with your main imaging camera hoping all that is working right.

I would stick my neck out and say so long as you're pointing in the general area of your target i.e. not off at 25 degrees or something, then you're not likely to see any errors that are not attributable to flexure, poor seeing or some other known issues with good guiding.

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The difference between the RA-axis and any scope/optical axis is called cone error. If you have a slight misalignment between your two scopes (imaging and guiding), this just means that they have a different cone error. A small cone error only affects goto accuracy.

Drift alignment can be done with any star close to the meridian/eastern horizon, and you turn the RA/DEC settings accordingly. But your mount doesn't care exactly where the star is. Cone error only makes the RA/DEC settings of the drift star slightly different. It doesn't affect drift alignment.

Otoh, a telescope with larger focal length will make drift alignment more accurate. If you have a large difference in fl between guide scope and imaging scope, that could be a reason to use the imaging scope and not the guiding scope.

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