EQMAC/EQMOD for PEC training?

[buzz]

On an EQ6 mount - the PEC training is via the laborious keypad. I understand that, unlike a LX200, I cannot train the EQ6 through PHD, because the EQ6 does not see any 'slew' controls.

As I understand it, EQMAC/EQMOD emulates the handset and will link to guiding software - so the question is;

Can I use pulse guiding through EQMAC (or EQMOD) to do PEC training automatically on an EQ6?

I did do a forum search but could not find any reference to this before.

[Merlin66]

If you're successfully using PHD for guiding...why do you want PEC???

[chrisshillito]

Why wouldn't you?

Guiding only corrects errors that have already occured. PEC can compensate for errors about to happen. PEC+guidng will out perform guiding alone particularly at longer focal lengths and when longer guide exposures are used. Of course PEC training is an additional hassle and whether the performance improvement results in a significant difference will depend entirely on on you setup and imaging conditions.

Chris.

[chrisshillito]

On an EQ6 mount - the PEC training is via the laborious keypad. I understand that, unlike a LX200, I cannot train the EQ6 through PHD, because the EQ6 does not see any 'slew' controls.

As I understand it, EQMAC/EQMOD emulates the handset and will link to guiding software - so the question is;

Can I use pulse guiding through EQMAC (or EQMOD) to do PEC training automatically on an EQ6?

I did do a forum search but could not find any reference to this before.

If you're talking about synscan based PEC then no you can't do that - not unless you wire up your own hardware/software to triger the direction keys on the sysncan in response to ST4 or pulse guide commands.

When EQMOD is used the handset is redundant and plays no part in controlling the mount. EQMOD provides its own PEC implementation and to use it all you have to do is capture an unguided log of star movement over several worm cycles (this can be done with PHD if you want). You then use PECPrep to analyse/filter this data in order to create a PEC curve for EQMOD to use. Its all on the EQMOD website and in the videos on youtube.

Chris.

[Merlin66]

On the limited number of occasions I've tried PEC and guiding, I really didn't notice any appreciable difference/ improvement.

The attached write up (from the EQMOD site) gives a good overview.

PEC_and_guiding.pdf

[chrisshillito]

Glad you like it - I wrote it :-)

My approach is that PEC is a useful option to have available in the toolbox. If properly recorded and synchronised it will improve the mounts tracking performance and this can, in some applications, lead to an improvement in guided performance. However, there are so many variables in play when considering the capture of an astronomical image and there is no guarantee that a small improvement made in one area will not prove to be totally insignificant in the context of other errors and variations that are present. Also poorly recorded/synchronised PEC will make things worse and adding another element into the mount control loop does not make configuration, maintenance and fault diagnosis any simpler!

Chris.

[buzz]

On the limited number of occasions I've tried PEC and guiding, I really didn't notice any appreciable difference/ improvement.

The attached write up (from the EQMOD site) gives a good overview.

Thanks Merlin, magic!

So to summarise - PEC is more useful when the guiding events are about 1second or longer apart and that EQMOD does its own PEC training, (I assume the synscan handset holds the PEC info) and if you connect in pcdirect mode to an EQ6 mount, EQMOD/EQMAC does not emulate the synscan handset button presses and that automatic PEC recording is not possible (as if you pressed the slew buttons yourself).

Thinking this through, when one does PEC training, it is doubtful that a human can respond to drift trends fast enough to outperform a 1-2 second guider timeframe anyway! That is a very important for anyone NOT using EQMOD to determine PEC and should be in the PDF file.

[chrisshillito]

Chris,

The synscan holds PEC data for Synscan PEC. The PC holds the data for EQMOD PEC. The two are totally separate. When in PC direct mode the sysncan just acts as a communications router to connect PC to mount - all synscan functions are bypassed.

Running PEC will provide a fixed improvement to the mounts tracking. If you are using long focal lengths or low resolution guiding (finder-guiders) or long guiding intervals you may find that the imprvemment in tracking delivers an improvement in the overall image. Whether this is important for your own astronomy you'll have to work out for yourself.

Human responses are fast enough for PEC training. PEC is only intended to correct for the mounts periodic error and this is very slow moving. For an NEQ6 think about a 15 arcsec amplitude sinusoid with a period of eight minutes. However the problem is that the error the eye (or autoguider) sees is not just periodic error. It consists of non periodic errors as well such as bumps, wind disturbances and seeing fluctuations and these move fast. You may also experience constant drifts dues to polar misalignment. Clearly errors such as there should not form part of your PEC and this is a good reason why it is actually bad idea to use an autoguider to do PEC training.

Chris.

[buzz]

Chris,

The synscan holds PEC data for Synscan PEC. The PC holds the data for EQMOD PEC. The two are totally separate. When in PC direct mode the sysncan just acts as a communications router to connect PC to mount - all synscan functions are bypassed.

Running PEC will provide a fixed improvement to the mounts tracking. If you are using long focal lengths or low resolution guiding (finder-guiders) or long guiding intervals you may find that the imprvemment in tracking delivers an improvement in the overall image. Whether this is important for your own astronomy you'll have to work out for yourself.

Human responses are fast enough for PEC training. PEC is only intended to correct for the mounts periodic error and this is very slow moving. For an NEQ6 think about a 15 arcsec amplitude sinusoid with a period of eight minutes. However the problem is that the error the eye (or autoguider) sees is not just periodic error. It consists of non periodic errors as well such as bumps, wind disturbances and seeing fluctuations and these move fast. You may also experience constant drifts dues to polar misalignment. Clearly errors such as there should not form part of your PEC and this is a good reason why it is actually bad idea to use an autoguider to do PEC training.

Chris.

Interesting - if I read this right, it suggests that the natural human filtering of slow periodic error is more helpful as a PEC input than the fast reactions to autoguiding, unless you use the FFT filtering in pepprep (ok, so I edited the last bit after reading up on Peprep). I used to be able to do FFT's too. When you are starting up, the learning curve can seem like the Eiger at times.