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Old 23-02-2014, 02:28 PM
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PRejto (Peter)
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PRejto is offline
Join Date: Jan 2011
Location: Sydney, Australia
Posts: 1,314
I've used PEMpro to drift align my MX and it is a very nice aid. But to say one is "spot on the pole" is not exactly correct as there is no such thing. There are various "poles" depending on what one wants to do and where one images in the sky (refraction), etc. It seems that all polar alignment is a compromise.

Now, with my MX (perhaps partly because of the issue it had with the polar axis) I had various difficulties with the T-Point polar alignment recommendations.** But, suffice to say, if one is close enough to PA, T-Point will do the rest regarding tracking corrections and will deal with flexure and mount inaccuracies (if repeatable). Anyway, the critical thing is that once PA is set, and a T-Point model constructed it is not OK to move the PA unless one re-calibrates back into the model and reestablished the ME and MA terms. (To do that one re-calibrates as a portable mount even if the mount is permanently set up.)

What I like about the PEMpro routine is that it gives a no drift situation at and near Dec = 0 which may be in the region of the sky where one wants to image. I personally found it faster to use than T-Point (for PA) as it doesn't need multiple iterations. It seems to be a reasonable compromise for PA and a reasonable PA to start a large T-Point run from. This is what I've done. I just ignore the PA report from T-Point once I'm happy with the PEMpro result. The large T-Point run then will give terrific pointing and excellent tracking.

Logan, are you still intending to use TSX/T-Point with your AP mount or are you changing all?


** In my experience T-Point can give some vexing results if one's view is restricted east or west. Mine is very restricted to the east but unrestricted to the west. Even though I collected points on both sides of the meridian there were far more points to the west. This seemed to skew my PA recommendations strangely. If I restricted collection of points to be equidistant E and W of the meridian I ended up with a polar alignment that was pretty close to the PEMpro drift alignment. I'm sure there could be a multitude of factors at play here so it is difficult to draw a conclusion from this. I will just say that given my conditions, and my particular MX this is what worked best for me.
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