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PEC question, general and specific

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#1 bunyon



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Posted 11 April 2013 - 08:36 AM

I've had my new AVX out a couple of times now as well as playing with it in the garage. Works great. I have no complaints at this point in regard to the mount.

However, I was looking at using PEC. As this is the first mount I've owned with PEC I'm not experienced. Reading the manual, it looks like one has to re-do PEC each time out. If you have to use an autoguider to do PEC, why not just let the autoguider guide through whatever PE there is?

I guess my general question is: how does PEC help where an autoguider is being used? My specific question is: is re-doing the PEC calculation each time unique to the AVX or is that in general how it is handled?

#2 Footbag


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Posted 11 April 2013 - 08:45 AM

I don't know about re-doing the calibration every outing. I would think it would store the PEC curve and let you play it back whenever. I'm not sure on this, I never used it on my CPC. My Mach 1 has a curve stored.

I typically ignored PEC and let the autoguider guide out the PE. I think Craig Stark says there is nothing wrong using both PEC and autoguiding, but I'm not convinced there is any real benefit.

#3 jrcrilly


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Posted 11 April 2013 - 08:59 AM

When PEC (Periodic Error Correction) was first implemented, neither the worm position nor the correction data were stored and thus it had to be redone for each session. Celestron's current EQ mounts, like all current gear with which I'm familiar, incorporates PPEC (Permanent Periodic Error Correction), and the old recording is simply replayed for each session. This means that either the worm position is stored or there is a worm index switch, and that the data is preserved.

#4 Cliff Hipsher

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Posted 11 April 2013 - 09:06 AM

This is almost exactly how AutoStar on my LXD75 works.

When you run PEC Training, Autostar moves the mount in RA and counts down from 150 to 0. While this is going on the user is supposed to use the keypad to keep a star centered. When PEC Training is finished you must PARK the mount. This is necessary to retain the synchronization between the REC data and the physical position of the worm gear.

If you power up the mount and do not park it before you power off, this synchronization is lost and you must run PEC training again.

Additionally, with AutoStar you can fine tune the PEC data by running PEC UPDATE. This is similar to PEC Training, and again you must park the mount to maintain synch.

From an imaging stand point, having good PEC data will tend to reduce guide inputs, which can lighten the load on your laptop CPU....

#5 jrcrilly


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Posted 11 April 2013 - 09:17 AM

how does PEC help where an autoguider is being used?

It depends on the mount. In general, the goal of PPEC is to get the remaining errors down to something that can easily be guided out. If the mount is easily guided without PPEC, it can be disregarded (that's why Takahashi mounts don't even offer PEC). If the mount is too wild without it, PPEC can be very helpful. I generally use it when it's available to me.

#6 cn register 5

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Posted 11 April 2013 - 01:26 PM

On the AVX the PEC is saved in the mount so once you have recorded it you can continue to use it. But you do need to turn it on each time.

I suggest using PECTool - a free download from Celestron. It connects to the scope using a serial cable and helps to automate collecting PEC data. It can be used to collect multiple runs of PEC data (10 minutes each), then average them and upload the averaged data to the mount.

It also means that the PEC data is saved on your PC so if you loose it in the mount - and I think a factory reset or updating new motor driver firmware will do so - you can restore it.


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