Re: Understanding APPM and Recals


Ray Gralak
 

Hi Marty,

I am trying to build an APPM model for my f/10 Cassegrain, now using a mono imaging setup with a 0.40 image
scale and variations on 1x1 and 2x2 binning, all with limited success. This leads to two questions.
Can you provide ALL of your APPM logs and PNT files, so that I can look through them? You can use the APCC log zipper utility. For now, I don't need APCC or ASCOM logs, so you can exclude them.

First, could I be getting spurious results? APPM keeps telling me that my telescope on the west side is off in RA by
as much as 12 degrees. This seems very strange. Twelve degrees is a lot. I've checked for cone error and it is
under 8 arc-minutes. The errors are only in RA, not DEC. The mirrors in the Cassegrain are fixed -- no mirror flop.
The model on the East side is far better -- pointing is off by 5-15 arc-minutes. What explanations are there for
such high pointing errors on one side (only) of the meridian? Could this be a result of my settings leading to
spurious solutions? Only about half of the model points result in a solution anyway. Note that I've done this twice,
with two different cameras, and got similar results.
12 degrees is a lot. Are you seeing that level of error consistently?

After you install the model, is pointing bad on both sides, or just the side with high errors?

How does a Platesolve/Recal executed through APPM work in cases where an APPM-built model is in already
place and in use? Does it modify the underlying APPM model in any way or just make a one-time adjustment for
where the telescope is at that moment pointing? Would that adjustment carry over to other pointing on that same
side of the meridian? In other words, can I gradually refine an APPM model by a series of Platesolve/Recals and
then save it as a new model?
PlateSolve/Recals do not add or refine the pointing model.

Similarly, how does a Recal ("Sync") work in TSX relative to an APPM model? I assume it doesn't change the
underlying APPM model at all. But will it apply the Sync adjustment to all pointing positions on that same side of
the meridian?
TSX Sync's will not change the pointing model.

-Ray

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