Celestron Advanced GT mount accuracy

[Andrew C]

I have an old (2003) Celestron Advanced GT eq mount that I have not used for a while. I have a 150mm Newtonian attached to it.

I've often wondered what performance I should be able to expect in terms of accurate slewing to find an object, as it seems to vary from very accurate (an arcmin or two) to maybe 20 arcmin in the same session. This is not such an issue with exchangeable eyepieces, but is a pain when I'm using the mount in conjunction with a video-astro camera, as the object often is outside the field and is then difficult to find.

I'm quite confident of my polar alignment to within 5 arcmin, and also the 3 star alignment procedure.

Does anyone have any thoughts on whether my expectations are too high for this mount, and/or whether the various refinements such as final alignment slewing from a particular direction to counteract backlash are important??

Thanks, Andrew

[ChrisV]

I used to have one and used it for live imaging. The accuracy you describes sounds familiar. I remember it wasn't as good as someone I knew who did similar live imaging with an HEQ5.

Chris

[Huey]

don't forget that the altitude of the object may also play a part. The closer to the horizon the more distortion etc.

Huey

[AstralTraveller]

Andrew,

That sounds about par. I used one with a 15cm frac and it could generally land an object in a medium power field. I suggest you use >3 alignment stars. I used 5-6 and I believe it improves the model accuracy. Be fussy about centering guide stars. Before I had a cross-hair ep I used a 7mm ortho and out-of-focus stars best estimate the centering. If your finder is well aligned you can use 'precise goto' (or whatever it's called) to hop to the object via a nearby calibration star. Use the finder to put the calibration star on the sensor then centre on the sensor. [I've never tried that but it sounds good :)]

David