Re: AP1100 autoguiding


Dear all,

Thanks for the very accurate and informative replies.

Indeed, « derive » was not the correct word, Oliv, You're right. I meant drift, of course. So sorry.

Unfortunately, I only own a Canon 650 DSLR, right now, and I'm almost sure that I cannot use it with Pempro or even perform a polar alignment with such a software like phd2 guiding. The astronomical camera will come more later, next winter.

I think the primary drift defect, is in dec, and comes from a bad polar alignment, causing also some imperfections when using the goto.

Gear re-meshing is a good idea. I will try it asap. I suspect that the precedent owner of this mount possibly never did it. I asked him yeasterday, but I'm waiting for his answer. He possibly rely on the only autoguiding/APCC to correct all the drift defects, and was successful, as his really good images prove it. Beside being a nice person, he is also a keen and competent astrophotographer.

Anyway, I will also check upon the orthogonality, and try to get a precise measurement of the drift, both in RA and dec. Actually, my scope is a C11edge, and it is set up on a 16'' losmandy dovetail saddle, such a system most probably being well orthogonal.

Will try the Lacerta Mgen, and, if not working properly, order a small autoguiding camera such as a zwo asi 120 or 290 mini.

Once more, many thanks for the help and advices. I will come back later, as soon as weather permits to perform some tests on the sky.

Oliv, I will contact you via Astrosurf or WA soon, if you like.



Le mardi 3 mai 2022, 03:44:24 UTC+2, Howard Hedlund <howard@...> a écrit :

Hi Christophe,

Congratulations on acquiring the 1100GTO.  You will love it!

Pointing errors can have several sources:
  • The most common cause of pointing errors is polar misalignment.
  • If the RAPAS was not properly calibrated, it may not give good results.  If it was calibrated incorrectly, it will certainly fail to give good pointing.
  • Orthogonality affects pointing, especially nearer to the pole.  Orthogonality problems show themselves most strongly after a meridian flip.
  • Pointing problems are almost never the fault of the mount.
As Oliv points out, one of the first things to determine is whether your drift is in RA, Dec or in both axes.  You can easily determine which direction on the chip is RA by stopping tracking for a short while in the middle of an image.  The streak that results will be in the direction of RA.

You will need to either create a good PE curve or autoguide.  If you received the copy of PEMPro that came with the mount, you can both cure the periodic error and fix the polar alignment at the same time.

You may or may not need to remesh the gears.  This can be quite easily tested using the instructions in our website's technical support section. 

Contact me at Astro-Physics for further assistance.


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