PEC ... can you use an autoguider?

[Gem]

Hi,

Out of curiousity... on a CGEM, could you set up for a PEC recording then use the autoguider to make the corrections during the 7 min cycle?
Does having PEC on make much difference if you use an autoguider anyway? :question:

[Ryderscope]

I've never been able to get the PEC working on my GM8 but I don't bother as the auto guider will make corrections in RA and DEC anyway. Technically I dont see that there should be a problem with running both PEC and the auto guider as the logic says that there should be less movement for the auto guider to correct. Others may have a different view.
R

[Gem]

Thanks.

Comprehensive PM received. Thanks also! :)

[loki78]

How did the PM answer your question, a few people are probably curious about the answer.

[MrB]

Hopefully the PMer will share with the rest of us?
I'm sure I would learn something from it, if not a few other people.
Particularly those new to guiding(myself included)

EDIT: snap! (@ Jon ;) )

[Gem]

Out of politeness - not sure if I should post the PM. It is up to the PMer to post.
I am grateful for the info. :)

[loki78]

That's OK, you needn't post the whole PM then, but share the answer with us, or now you have the information, answer it in your own words.

[Gem]

" ...When collecting PEC data Autoguiding needs to be turned off otherwise it corrects the imperfections and the PEC collection process is ruined, but once you have collected and applied PEC there is every reason to want to continue using Autoguiding !

PEC only attempts to correct for the irregular "bumps" in pure sidereal movement, primarily caused by the normal mechanical deviations from perfection that exist in almost all gears made by man !
eg most spur gears are cut with 3-5 straight or semicircular cuts to approximate a curve that is an involute curve.
Hence PEC tends to be almost entirely aimed at the complex combination of all the different periods of rotation for each gear in the gear train.

Guiding attempts to correct for all the other errors put together - Atmospheric refraction changes with altitude, temp and barometric pressure, Sidereal tracking rate errors, backlash and other mechanical errors that include incorrect polar alignment.

So anything that can reduce the job the autoguiding correction does is a good thing.
Hence exceptional Polar Alignment, absolute rigidity in the pier and all adapters, good quality mount, Tpoint mapping for software correction of other mount and OTA related physical errors (eg non orthogonality, flexures of all sorts, backlash . . . .) and then all sky pointing correction with software such as ProTrack.

So PEC only performs but one of the many necessary functions to try to reduce the "noise" in our image acquisition systems ... "

Thanks to the source of the above info. :thanx:

[joecool]

aa

[Poita]

If you are training the system to collect PEC data then i would think that you would not auto guide while trying to collect the data. You want to collect the data of the mount anomalies, and guiding at that point would only confuse things.
Guiding on an already PEC trained mount is another thing altogether.

[joecool]

aa

[Visionoz]

Poita is not confused!!

You do not use the autoguiding because you want to get the "raw" PE characteristics of the worm/gear whilst it is tracking - and you actually are "recording" the corrections that you would make manually in order to smoothen the motions when tracking (as if it is autoguided) - this recording is generally done for a few worm cycles (ie how long it would take for the gear to turn one complete cycle) - when this "recording" (which actually contains all the corrections needed to correct the PE of the particular mount) is then used to "train" the mount through the PEC option - so basically the "corrected" PE is what is now superimposed on each worm cycle as it tracks and thus would provide supposedly good tracking (minus the PE) so to speak and of course coupled with autoguiding would provide very good tracking since you've already "removed" or "corrected" the inherent PE of the mount

HTH
Cheers
Bill

[MrB]

Yeah I had a feeling that wasn't quite right.
I was thinking that if there was a slight breeze, not a gust, just a real light breeze, enough to shift the image a couple of pixels for a little while. Or maybe something in the image train shifts or flexes just a little. Random events.
The autoguider would attempt to correct this and meantime it is recorded and subsequently this PEC+guiding correction would be applied every time. Breeze or no breeze. A random event recorded over a cyclic event.
Makes sense to me to have autoguiding off while recording PE.

[joecool]

aa

[Poita]

You are not guiding, but you are using a camera to watch a star so that the software can see how much that star appears to move and then use that data to record the PEC required.

Joecool, if you want an answer to a question, the best thing to do is ask it, and provide as much information as possible.

Start a new thread, title it "Help Please...How do you PEC train a CGEM" or something similar.
List the equipment and software you are attempting to use. (camera, software, mount etc.) and someone that has your specific setup will chime in to help.

Also, I just googled "pec train cgem" and there were pretty comprehensive answers on the front page:
e.g. http://www.astronomyforum.net/telescope-mounts-forum/110531-cgem-pec-training-phd-autoguiding.html

Start a help needed thread, don't yell (ALL CAPS) and post your info and I'm sure you'll get some help.

Cheers

-Peter

[Gem]

Not really sure about the info on that thread. It shows a huge improvement in DEC. Shouldn't PEC training only affect RA? Maybe I am wrong...

[Visionoz]

Hi Mark

Please don't get too stroppy with any of us that didn't provide you with the answer to a doubt you had that we could not read your mind of!!

I posted only because I thought that it best that clarification be given in regards to how one would do a PEC recording in relation to the PE of an EQ mount - yep, +1 to what Peter (Poita) said about asking - it surely would get a proper response when asked politely - I generally don't post here except if I know the answers to the queries asked or if I need to find out about something - I can read the manual (better known of as RTFM) for the CGEM if you really want me to do it for you and I'll then post a reply as to how you can do it because I personally have no experience with the CGEM

However in relation to your question: "What are you guiding on to train the PEC then?" I can explain to you that it is on a star of your choosing and then do a manual guiding (like the way it was done in those days before autoguiding became available) ie when you're tracking on that star you will need to use the handcontroller's 4 directional arrows to make all the corrections needed to ensure that the star stay spot on in the middle of your reticuled cross-haired EP all the time through several cycles of the worm rotations - the corrections that you make manually are recorded and it is this recording that gets used as the correction curve for the PEC process - I really don't know if this is how CGEM is applying the technique to its PEC feature

HTH
Cheers
Bill

[Visionoz]

OK Mark

I've found this which might help others interested as well: here (http://www.cloudynights.com/ubbthreads/showflat.php/Cat/0/Number/4295383/Main/4294455)

Hope that answers your query as well Grant's (Gem) the OP

Cheers
Bill

[joecool]

aa

[Poita]

By all means use the autoguider to make the corrections during PEC training if your mount handles this properly.

The crucial part is that the autoguide corrections are read by the PEC monitoring software so that the corrections are being recorded as the PEC data.

Do not use an inependant guidance system if the PEC monitoring software does not know about it, otherwise the data you are collecting will be junk.

Some systems do not handle being guided during the PEC training process, they merely track the deviation of the star being monitored in a camera. As I said, I don't know how the CGEM handles it, or what software they are using to do the PEC training, so it is difficult to give an exact answer without more info.

[rally]

Guys are you arguing about two different things here ?

Autoguiding with a PEC enabled mount ?
Autoguiding while trying to collect the initial PEC data ?

Quite different questions with quite different answers, that may vary with the gear and software in use.

The PEC data collection process needs to be within one loop, so you cant have extraneous corrections going on that the PEC program doesnt understand is happening or at least is managing itself in some way.

Once you have PEC enabled then you have (hopefully !) corrected much of the mounts periodic errors and autoguiding is now only trying to keep up with all the 'other' problems but not periodic error.

During PEC data acquisition the software frequently uses the guider port to make the corrections, but it knows its making these corrections and adjusts the data it records for those corrections.
But different systems do things in different ways.

I have no experience with the CGEM process, so I cannot speak for that one.

[Poita]

What Rally said :D