Re: Polar Alignment - RA & Dec Fight

Steven Waldren

Thanks for the help. Was able to use the thickness of 3 aluminum can sides to fix the cone error.  Use ConeSharp application.


On Jul 25, 2017, at 7:50 PM, chris1011@... [ap-gto] <ap-gto@...> wrote:

-----Original Message-----
From: chris1011 <chris1011@...>
To: ap-gto <ap-gto@...>
Sent: Tue, Jul 25, 2017 3:15 pm
Subject: Re: [ap-gto] Polar Alignment - RA & Dec Fight

Drift alignment:

My refined technique is to align azimuth first on a star on the celestial equator, not worrying about RA drift, Just zero out Dec drift there. Then, once that is done, i go to a star near the zenith (usually on the East side within 1/2 hour) and align the altitude axis by zeroing out the RA drift. Done this way, the two adjustments are independent and don't interfere with each other. The adjustment can be done in about 15 minutes.

Doing it this way gives me essentially zero RA and zero Dec drift over a wide area across the zenith. Of course, this does not align the pole exactly, but I'm more interested in no drift over a wide area versus best pointing. Even with my 17" F8 astrograph (3454mm FL), I can land just about every deep sky object somewhere on the STL11K chip. A simple pointing model can then align your scope to the sky further if you wish.

Orthogonality alignment:

I have also found a super easy way to get the orthogonality error down to near zero after the mount is aligned per the above drift method. It does not require any fancy flipping of the axes back and forth. It is simply this: Do a GoTo to Polaris. The star will not be in the center (eyepiece or CCD image) if you have any orthogonality error. Put the star as close to center in Dec with the N-S buttons. You will find that it will not move with RA with the E-W buttons. However, if you push a bit on the telescope tube in the RA direction, you will see the star move either toward or away from the center. Determine which way the tube must move to end up toward the center. Loosen either front or rear scope rings and slip a thin shim under the rings (.005" to .025" as needed). With the right amount of shim, you can get Polaris exactly in the middle in the RA direction while using the N-S buttons to adjust the Dec direction. 

I did this with my 17" astrograph, which needed about .020" shim under the rear rings. I can now go from one side of the meridian to the other and put every object on the chip without going to a bright star first. How long did it take me to do this? About 8 minutes, and worthwhile to do. No software compensation can eliminate this error near the pole, but this simple mechanical align can get you dead nuts on every time.


-----Original Message-----
From: Steven Waldren swaldren@... [ap-gto] gto@...>
To: ap-gto gto@...>
Sent: Tue, Jul 25, 2017 9:29 am
Subject: Re: [ap-gto] Polar Alignment - RA & Dec Fight

EDIT: “... West horizon and drifted in Az.” <— Should’ve said Alt not Az.

On Jul 25, 2017, at 9:14 AM, Steven Waldren swaldren@... [ap-gto] <ap-gto@...> wrote:


I had a interesting experience last night trying to polar align my MACH1, which is portable on a tripod. After polar aligning with my RAPS, I went to check with a drift align in PHD2. I drifted in just east of the meridian and was off by a couple of arc-minutes. I adjusted to within 1 arc-minute. I then slewed to the West horizon and drifted in Az. It was apparently off by over 10 arc-minutes. I adjusted to under an error under 1 arc-minute. When I slewed back the original star I drift aligned Alt on, PHD2 said it was off by 14 arc-minutes. I then adjusted Az to get polar error under 1 arc-minute. Then using PHD2 guiding assistant, I checked the polar alignment error, which was calculated at 4.5 arc-min. 

Any tips on what to check or what user errors I may have to cause an adjustment in Alt to effect alignment in Az (mount spirit level appeared level). During calibration of PHD2 I did not get any errors and I don’t think I deviated from my normal routine, which usually works well.


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