CGEM TPoint Test Results

Well here are the results of the TheSkyX TPoint model test that I promised that I would provide. I am not happy with the results, I was actually wishing that my gut feelings were wrong and that the RA-DEC orthogonality would have been acceptable with my Celestron CGEM telescope mount. In short it is not, here are a couple of screenshots of the programs results:


The RMS value for the mount pointing is 181.0 arc-seconds. The RA-DEC non orthogonality (TPoint calls it HA and Dec Non-perpendicularity or NP) was 1588.73 arc-seconds or about a whopping 26.5 arc-minutes! Good God the single most critical design aspect of any dual axis mount is its orthogonality and Celestron’s subcontractors can’t even get that right HORSE SHET QUALITY CONTROL through-in and throughout. According to the TPiont manual the Sigma figure should be less than 1/3 of the term value for it to be statistically significant or valuable, and they indeed are.

Also the OTA-Dec non-perpendicularity was combined with HA-Dec, but prior to building the above model the OTA-Dec non-perpendicularity was less than 100 arc seconds so was not nearly as significant as the HA-Dec non-perpendicularity.

I would like to point out that it was a real pleasure to use both Software Bisque’s TheSkyX and their integration of TPoint software. When using this software the mount falls into the background where it belongs. From initial polar aligning to acquiring enough calibration stars from several constellations from all over the available sky took less than one hour. It is so rare that today real top quality useable products are still obtainable.

When initially calibrating the first couple of stars the finder scope was needed to position the stars within the sensor range of the Orion Starshoot Autoguider and the 400 mm Orion guide scope. TheSkyX thereafter was able to point close enough to subsequent stars such that they were just outside of the bullseye in the PHD software’s viewfinder. Much finer results than when using the CGEM’s hand controller and all four calibration stars. Also note that TPoint was also able to determine the flexure of this setup, not very good even though everything was tight as could possibly be, another story for another time.

(I have no affiliations nor have I received any compensation or considerations from any company or any persons in any aspect of this or any of my previous reviews)


Update added 2012-10-03:

I did a second TPoint calibration run that resulted in a pointing error of 28.6 arc-seconds RMS and using a much closer polar alignment with a total of 6 arc-minutes error. The results for the combined non-perpenducualrity were actually worse at just over 30 arc-minutes, just over one-half a degree or greater than the angular width of the Moon. The sigma figure was less than 50 for the non-perpendicularity indicating an even greater statistical significance from my original calibration run.