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Does focal length affect PEC training?

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#1 mchaser

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Posted 17 May 2009 - 11:16 PM

Please pardon me if I'm being dense, but I started wondering about this. Using the same imaging CCD, wouldn't periodic error appear larger when imaging through an 8" SCT and smaller through a 4" refractor? After all, each has a different pixels/arc second. It would seem that the error graph would be similar, but with a different amplitude. If that's the case, do I need to train for each scope/imager combination, and upload to the mount as needed?

If I'm wrong (and I usually am) can someone please explain why?

My humble thanks to the bigger brains out there. I've given myself a headache already...

#2 WadeH237

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Posted 17 May 2009 - 11:50 PM

Periodic error is a mechanical error in the mount itself that is independent of the focal length of the telescope.

Periodic error correction is a feature where the mount (or other software) stores a set of corrections that can be used to cancel out the error. These corrections are measured by the direction, amount of time that they are applied, and the speed of the RA drive while a correction is applied. The corrections are therefore not dependent on the focal length of the telescope.

With my CGE, I analyze periodic error about once every couple of years and program the mount with the data. When I run periodic error correction playback, it works fine with all of the different OTA and camera combinations that I use.

-Wade

#3 Alph

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Posted 18 May 2009 - 01:45 PM

wouldn't periodic error appear larger when imaging through an 8" SCT and smaller through a 4" refractor?


Yes, it would be more visible at longer focal lengths. The reason being, the longer focal length the higher image resolution and it is easier to notice the effect of PE.

#4 JAT Observatory

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Posted 18 May 2009 - 05:54 PM

When I do PEC training I use the longest focal length available to me.

#5 mchaser

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Posted 19 May 2009 - 12:27 AM

Got it. Thanks for the help!!






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