PEC - worth it on a temporary setup?

[Demonperformer]

Tried to get this question answered on another thread, but kept being shouted-down - I guess that was OP's way of saying go and start your own thread, so I am.

Is PEC worth doing on a mount that is totally disassembled at the end of each session and rebuilt for the next one? The reason I ask is that I had a play with PEC a few years' back and made a right mess of it while trying to eliminate all the different elements of the curve and ended up with worse tracking than before, so (typically) gave up. Now @vlaiv  has given a step-by-step procedure that looks a lot simpler and I am beginning to get guiding working (even if it's having to work extremely hard, but that's another story!). I am convinced that PEC will make guiding easier once it is done, but would PEC work in this situation? I am not going to waste spend an hour or two of imaging time training the mount every clear night I get!

Thanks.

[Wiu-Wiu]

PEC is essentially teaching your mount how to anticipate on errors in its own gear. 

I have learned that having PEC AND autoguiding will usually fight against each other, it could be compared to having two bosses telling you how to do your job, without knowing what the other one is doing. 

 

It IS good to teach your mount PEC, even on a mount that is taken inside every night, but if you are going to guide, I would turn PEC off. 

[vlaiv]

3 hours ago, Demonperformer said:

Tried to get this question answered on another thread, but kept being shouted-down - I guess that was OP's way of saying go and start your own thread, so I am.

Is PEC worth doing on a mount that is totally disassembled at the end of each session and rebuilt for the next one? The reason I ask is that I had a play with PEC a few years' back and made a right mess of it while trying to eliminate all the different elements of the curve and ended up with worse tracking than before, so (typically) gave up. Now @vlaiv  has given a step-by-step procedure that looks a lot simpler and I am beginning to get guiding working (even if it's having to work extremely hard, but that's another story!). I am convinced that PEC will make guiding easier once it is done, but would PEC work in this situation? I am not going to waste spend an hour or two of imaging time training the mount every clear night I get!

Thanks.

What mount are we talking about?

If your mount has PPEC - permanent PEC, then you don't have to worry about it - you do it once and mount remembers it. If you happen to have Synta mount without PPEC, like HEQ5 or EQ6 - then you have to be careful in one thing - you need to park your mount at the end of each session and there should not be power loss during the session. PEC is stored in EQMod, and mount does not know "where it is" - your lap top knows, or rather assumes that mount is at park/home when you first start up. For this reason you need to park to home after each session before you turn your mount off so that sync between EQMod and mount is preserved.

I'm running PEC on my HEQ5 and I don't have permanent setup. I dismantle mount after each session but follow above advice. I've also had my power lost during one session and I can confirm that PEC sync is lost on such occasion.

2 hours ago, Wiu-Wiu said:

PEC is essentially teaching your mount how to anticipate on errors in its own gear. 

I have learned that having PEC AND autoguiding will usually fight against each other, it could be compared to having two bosses telling you how to do your job, without knowing what the other one is doing. 

 

It IS good to teach your mount PEC, even on a mount that is taken inside every night, but if you are going to guide, I would turn PEC off. 

This is long standing belief that somehow PEC and Guiding will fight each other, and that is probably true in some cases. It really depends how PEC is implemented. If your mount / driver performs PEC by issuing pulse guide commands at certain intervals then yes two conflicting pulses can "fight" each other. On the other hand if your PEC is implemented as VS-PEC, or variable speed PEC then they actually work together. In this case PEC is not applied via pulse guide commands, but rather speed of RA motor is altered to speed up or slow down the mount to counter act to PE. Guide pulses will work as usual, as if there was no PEC running, and in the fact you will have better guiding performance because smaller corrections will be applied and less often.

[Demonperformer]

Thanks, vlaiv. Mine's an NEQ6, so your advice is precisely what I needed. I will give it a go.

[Demonperformer]

Neil (@Stub Mandrel) has suggested an option on the latest version of PHD2 - Predictive PEC. Going to take a look.

[vlaiv]

3 hours ago, Demonperformer said:

Neil (@Stub Mandrel) has suggested an option on the latest version of PHD2 - Predictive PEC. Going to take a look.

Two very different things, and you can run them side by side.

PEC, regular one, is meant to correct for "medium" frequency periodic error - one that is harmonic of base frequency of worm. In HEQ5 for example, worm period is about 10 and a half minutes. PEC tries to correct components that are 10.5, 5.25, 2.625, ... minutes long (maybe 3-4 first harmonics).

PPEC is "realtime" algorithm. It would take at least a few full cycles for it to learn full PE worm period - this means that you would "waste" an hour or two of imaging time for algorithm to learn your mount each time. It will get progressively better as your guiding session moves forward, but you want your guide session to be as good as it can be from the start.

What regular PEC can't do is handle very short period errors which some mounts have - things that are not harmonics of main worm period, and usually have 15-30s period. Example of that is 13.6 second gear mesh period on HEQ5. This is where PPEC steps in - it monitors short period oscillations and starts correcting for them very fast, after just a few minutes - because after few minutes it already has half a dozen complete periods that are 20-30s long recorded and can analyze them.

So in essence they regular PEC and PPEC can work together if you have issues with short period errors.

[Demonperformer]

You have effectively answered the question I was coming back to ask before I asked it - I was wondering if Predictive PEC would "remember" what had happened during the last session in the way you have said PEC does ... obviously not. So both are worth having.

On a slightly different issue, you have (on another thread) mentioned autoPEC in EQMOD. As this is done with guiding switched on, does this mean you can record this while actually imaging as opposed to losing the first hour or two to do the recording?

Thanks.

[vlaiv]

42 minutes ago, Demonperformer said:

You have effectively answered the question I was coming back to ask before I asked it - I was wondering if Predictive PEC would "remember" what had happened during the last session in the way you have said PEC does ... obviously not. So both are worth having.

On a slightly different issue, you have (on another thread) mentioned autoPEC in EQMOD. As this is done with guiding switched on, does this mean you can record this while actually imaging as opposed to losing the first hour or two to do the recording?

Thanks.

Yes you can. I would not do it though as you will end up with two different sets of subs, or rather range of star FWHMs across the session if there is significant improvement with PEC. On the other hand - we end up with different star FWHMs just by virtue of changing conditions, so my previous point is moot one .

In my defense, I would not do autoPEC in the first place, as I like "traditional" approach.