Re: An easier Pasillx N & S Polar Alignment method

Joe Zeglinski

Hi Rick,

In the Orthogonally section of the latest GTO Keypad manual, it states that:
"especially in GEM mounts, a non-orthogonal mount will cause errors in ANY routine that uses the scope for polar alignment (e.g. N Polar Calibrate routine) ..."

So, I assume this is true for all other routines, including Quick Drift, which does not make it a secondary issue of concern, and certainly necessary. The routine to square it up is essentially identical to the one describing Roland's GTO Quick Star Drift Method using Meridian Delay - except rather than adjusting mount's azimuth adjuster , you use metal shims to prop up the OTA.

The only mention of using the finder is if the mount alignment (or I suppose orthogonally) is way off, and the reference star is out of the field. In such case, the manual states using the finder, for the first iteration, before trying the OTA again.

As far a I can tell, getting the OTA orthogonal is the first concern (assuming it is carrying a finder aligned with its optical axis already). Once the OTA/finder are trued up, you should align the mount.

However, I must say, there seems to be a "chicken and egg" quandary here.
For the Quick Drift Method, you need a properly aligned mount to run the orthogonally test, BUT, the OTA has to be orthogonal to begin with, in order to align the mount.

Based on the east-west drift during that procedure, how do you know whether the drift is caused by a misaligned mount, or a non-orthogonal OTA?

I suppose, you could just assume the OTA is aligned, and IF you can't align the mount after many iterations, ONLY then assume the OTA is non-orthogonal, and repeat the tests, BUT this time use "shims" under the OTA rings, rather than the AZ adjuster.
Does this make sense? I don't recall it being stated this way in the manual.

As for the finder in Roland initial discussion, if it is physically part of the mount, then you still have to run the two procedures for the finder of mount alignment - followed by (if needed), finder orthogonally shimming (i.e screw adjustment).
You can't do the same if the finder is on the OTA, since you could have both the finder and the OTA individually non-orthogonal. That is why it seems best to align the finder with the OTA using a special eyepiece - perhaps in the daylight, on a distant object.

Yikes !


----- Original Message -----
From: "Rick K" <JunkMailGoesHere@...>
To: <ap-gto@...>
Sent: Saturday, September 20, 2008 9:12 PM
Subject: [ap-gto] Re: An easier Pasillx N & S Polar Alignment method

I am glad Roland brought up using a finder. The whole point of the
meridian flip method is to polar align the mount. Making the optics
perfectly orthogonal is secondary and unnecessary. It might make
things a little simpler to understand if you do both as Roland
describes, N-S for the inclination error and E-W for the orthogonal
error when using the meridian delay flipping. Using the finder seems
to really speed things up and if one wants to get super accurate,
going to a CCD technique in the main instrument would quickly
fine-tune the polar alignment. I like it!

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