Re: consistent goto error on meridian flip w/1200

Steven Panish

Thanks for the input, Roland.  It always seemed most likely to be orthogonality related to the dovetail bar on the C9.25.   All the AP stuff I trust.  The software compensation feature sounds great...but I have a CP3.  I'll try shimming first, which will be a bit of a random walk combined with a binary search.  


On Sun, Nov 15, 2020 at 12:55 PM uncarollo2 <chris1011@...> via <> wrote:
Typically the mount is very accurate as far as orthogonality. I have measured the gearwheel accuracies of a number of mounts and they consistently fall below 15 arc seconds for the entire 360 degree rotation. In other words, the gearbox and worm wheels are extremely accurate and would not impact the orthogonal error that you experience.

The main culprit is usually the optical tube assembly. The optical axis of a telescope does not always line up precisely with the mechanical mounting of the tube. A 1 degree error of the mounting system will produce a 2 degree pointing error when flipping from one side to the other. The solution is to measure the pointing error an shim the tube assembly or mounting rings to eliminate the mechanical error. The other solution is to compensate for it with software. We now have incorporated an automated routine in the CP4 and new keypad software that measures the ortho error and compensates for it.

Roland Christen

-----Original Message-----
From: Steven Panish <scpanish@...>
Sent: Sat, Nov 14, 2020 7:31 pm
Subject: [ap-gto] consistent goto error on meridian flip w/1200

My venerable 1200 has a large and consistent goto error after a meridian flip.  It is roughly 2 deg in RA and a couple minutes in Dec, I haven't actually measured it.  Very consistent, so in spite of being way off the sensor I know how to move the scope E/W to get the target back in sight.  After a recal, goto accuracy is restored.  This isn't mirror flop, the finder scope also shows the issue and I can use that for centering as well.  Mostly I avoid the problem by starting an imaging run counterweight up and avoiding a meridian flip altogether.  I bought this 1200 3 years ago and it has always had the issue.

Does anyone have a clue as to what is wrong?  Orthogonality?  The scope is a C9.25 and the finder is mounted on the scop so the dovetail could be off, everything else is AP and should be precise.   I can work with it but it would be nice to not have to think about it.  


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