EQmod PEC

[alan potts]

Has anyone tried the newish EQmod PEC, all I see on line is an older video of PEC where one had to use a separate program to generate a PEC file the edit and load.

Now I see in the opening window there is a record PEC facility and play button, you record 5 turns of the worm which I imagine takes a time and then I guess play it back whilst guiding

Anyone done this as I don't see very much at all that's up to date, as good as guiding was last night before clouds visited we always want that extra bit to go to 11 as Spinal Tap would say.

Alan

[almcl]

I've used the Autorecord PEC function.  Not a fan of web instructional videos, so I followed the work flow that starts on page 9 of this document http://eq-mod.sourceforge.net/docs/eqmod_vs-pec.pdf

However, I recently found something better.  If you have an AZ EQ6, as I believe you do Alan, and the latest version of EQMOD it is possible to get the mount to record its own permanent PEC and to have it play it back.  The instructions I followed are over on cloudy nights combining eqmod with ppec and phd2

The idea is that with the mount taking out the larger errors (probably the worm period ones) PHD2 is then able to deal with the other ones.

Getting a smooth PEC curve recording took some doing - clouds kept intervening -  and I haven't had a chance to check it with a long guiding session under good seeing conditions yet, but initial results look hopeful.

[alan potts]

2 hours ago, almcl said:

I've used the Autorecord PEC function.  Not a fan of web instructional videos, so I followed the work flow that starts on page 9 of this document http://eq-mod.sourceforge.net/docs/eqmod_vs-pec.pdf

However, I recently found something better.  If you have an AZ EQ6, as I believe you do Alan, and the latest version of EQMOD it is possible to get the mount to record its own permanent PEC and to have it play it back.  The instructions I followed are over on cloudy nights combining eqmod with ppec and phd2

The idea is that with the mount taking out the larger errors (probably the worm period ones) PHD2 is then able to deal with the other ones.

Getting a smooth PEC curve recording took some doing - clouds kept intervening -  and I haven't had a chance to check it with a long guiding session under good seeing conditions yet, but initial results look hopeful.

Yes I happened across it the other night, idle hands again, clicking buttons an saw it in the opening EQmod window with the N S E & W controls. It looks like 5 turns of the worm, which as you say is a while, at least 40mins I would say. I do indeed have that mount, I will give this a read and have a play tonight as the Moon is now annoying.

Alan

[Stub Mandrel]

I use it now, it's really easy. I haven't made any exact measurements but I see my guiding improve over the first twenty minutes to half hour and I am definitely seeing better guiding since I started using it.

For the DEC I find that 'resist switch works best.

[alan potts]

12 hours ago, Stub Mandrel said:

I use it now, it's really easy. I haven't made any exact measurements but I see my guiding improve over the first twenty minutes to half hour and I am definitely seeing better guiding since I started using it.

For the DEC I find that 'resist switch works best.

SM, can you tell me which one you actually use and briefly how. I had a read and took some subs last night and found it a little confusing, not difficult for me, there seems to be a few ways to skin a cat.

I think I will try for automated one and auto load, but then as I get more confidant try to doctor the file in PECprep, which I see you can do, this guiding can get a bit obsessive, most of last night I was below .5 sec or something like .3 pixel, but them every now and then, with no real pattern, bang, a spike at 1sec plus, on Dec mainly and my PA is under 1min. That is according to Polar align and guide assistant. Most of last night Dec was a straight line.

Alan

[Stub Mandrel]

Predictive PEC on RA and Resist switch on DEC. Recently I've had constant 0.65"  with the 130P-DS which is (according to Vlaiv's calculations) as good as the HEQ5 (or an EQ6) can be be expected to deliver because of the step size.

I PA with Sharpcap, typically to better than 0.2'.

The heavier 150PL I get slightly higher figures.

[alan potts]

3 minutes ago, Stub Mandrel said:

Predictive PEC on RA and Resist switch on DEC. Recently I've had constant 0.65"  with the 130P-DS which is (according to Vlaiv's calculations) as good as the HEQ5 (or an EQ6) can be be expected to deliver because of the step size.

I PA with Sharpcap, typically to better than 0.2'.

The heavier 150PL I get slightly higher figures.

I am running the PPEC now but I thought this stood for Permanent, wrong again. I was to try the minimum 5 turns of the worm PEC.

Alan 

[Stub Mandrel]

Have you seen:

https://openphdguiding.org/man-dev/Guide_algorithms.htm

Quote

 

Since PPEC employs a learning process, it will usually take about 2 worm periods to model the mount and become fully effective.  During this training period, the algorithm will behave more like the ‘hysteresis’ algorithm, so you won’t normally see a performance penalty while the internal model is being built.  Instead, you’re likely to see a steady improvement in tracking as the model is refined and the algorithm shifts seamlessly from hysteresis to predictive-mode.   This improvement can usually be seen even before the medium-term mount behavior is fully modeled.

 

[alan potts]

Stub,

This was something that some one touched upon the other day, I have to confess I have never seen it before though did hunt down the area in PHD without understanding anything, nothing new there. This is yet another to read up on.

The PEC I was looking at and the PPEC that I am using sits in EQmod. PEC is a run of 5 and upward rotations of the worm recorded in the opening control panel of the program, you get to the various sections by clicking on the Green Cross on the upper left hand side. This can create a file that can if you wish be doctored in PECprep, another program, this seems a fair bit more advanced than I am comfortable with at the moment.

The PPEC I am actually using, if indeed I am using anything at all other than imagination, sits int he open out menu EQmod on the far right hand side. This has a record/play refresh section, dependent upon whats happening in the routine running list will pulse the mounts LED, 1,2 and 3 time, 3 times meaning it's running.

Maybe this is interlinked in some way to PHD2 PPEC, but I feel the PEC section is EQmod specific and is stand alone and in no way connected.  I was going to have a go tonight but it was patchy cloud.

Alan 

[Stub Mandrel]

48 minutes ago, alan potts said:

Stub,

This was something that some one touched upon the other day, I have to confess I have never seen it before though did hunt down the area in PHD without understanding anything, nothing new there. This is yet another to read up on.

The PEC I was looking at and the PPEC that I am using sits in EQmod. PEC is a run of 5 and upward rotations of the worm recorded in the opening control panel of the program, you get to the various sections by clicking on the Green Cross on the upper left hand side. This can create a file that can if you wish be doctored in PECprep, another program, this seems a fair bit more advanced than I am comfortable with at the moment.

The PPEC I am actually using, if indeed I am using anything at all other than imagination, sits int he open out menu EQmod on the far right hand side. This has a record/play refresh section, dependent upon whats happening in the routine running list will pulse the mounts LED, 1,2 and 3 time, 3 times meaning it's running.

Maybe this is interlinked in some way to PHD2 PPEC, but I feel the PEC section is EQmod specific and is stand alone and in no way connected.  I was going to have a go tonight but it was patchy cloud.

Alan 

AH! I am using the PHD2 vesrion. My advice is try it as (a) it only takes two worm rotations to start working and (b) you can gather subs over that period.

[almcl]

There are, confusingly, two PPEC s. 

Within PHD2 there is Predictive Periodic Error Correction, a great algorithm in my experience (or at least my guiding seems better with it).  Then there's EQMOD's PEC and finally there's the Skywatcher mount's Permanent Periodic Error Correction (Page 18 of the Skywatcher manual).

According to the PHD2 gurus, PHD2's PPEC  can be combined with and work well with the mount's PPEC.  And the thread on Cloudy Nights (referenced in post 2 above) also suggests that they can be adjusted to work together to eliminate different frequencies of the overall error.

Not sure if that's made anything clearer?

[symmetal]

I wasn't aware of the PHD2 PPEC and will give it a try next time. It sounds useful.

The Eqmod PEC once recorded is applied continuously from then on while tracking. This requires the PEC corrections to always know the current phase of the worm gear cycle. If these get out of step by the mount getting knocked or manually slewing with the mount off, the PEC corrections then get applied in the wrong place making things worse. This happened to me a couple of times and having to record the PEC again is a pain. There was no way of knowing if the PEC was in or out of phase so I never bothered with it again. This was a few years ago. Whether it is better now and can keep itself in step better I don't know.

The PHD2 PPEC looks promising as it's reset for each new target. After learning the PEC corrections over 2 cycles (while imaging so no time lost) it is applied only while imaging that target. It also handles dither OK. If you then slew to another target, it starts the PPEC learning process over again so it doesn't need to keep track of the phase of the worm cycle so won't get out of step.

You can therefore use both PEC corrections together as almcl says, as the PHD2 PPEC will just correct for the errors left over after applying the Eqmod PEC.

Alan

[alan potts]

7 hours ago, almcl said:

There are, confusingly, two PPEC s. 

Within PHD2 there is Predictive Periodic Error Correction, a great algorithm in my experience (or at least my guiding seems better with it).  Then there's EQMOD's PEC and finally there's the Skywatcher mount's Permanent Periodic Error Correction (Page 18 of the Skywatcher manual).

According to the PHD2 gurus, PHD2's PPEC  can be combined with and work well with the mount's PPEC.  And the thread on Cloudy Nights (referenced in post 2 above) also suggests that they can be adjusted to work together to eliminate different frequencies of the overall error.

Not sure if that's made anything clearer?

All very confusing, there is also a PPEC within EQmod as well which I briefly describe above. I am going to give the PHD2 version a try in any case. My guide with the PPEC in EQmod seems to be better than without it so I am sure it does something.

Read the Sky Watcher manual it would appear to be very much the same. Over all my guide is fairly decent, it just has the odd blip that would be nice not there.

Alan

[alan potts]

6 hours ago, symmetal said:

I wasn't aware of the PHD2 PPEC and will give it a try next time. It sounds useful.

The Eqmod PEC once recorded is applied continuously from then on while tracking. This requires the PEC corrections to always know the current phase of the worm gear cycle. If these get out of step by the mount getting knocked or manually slewing with the mount off, the PEC corrections then get applied in the wrong place making things worse. This happened to me a couple of times and having to record the PEC again is a pain. There was no way of knowing if the PEC was in or out of phase so I never bothered with it again. This was a few years ago. Whether it is better now and can keep itself in step better I don't know.

The PHD2 PPEC looks promising as it's reset for each new target. After learning the PEC corrections over 2 cycles (while imaging so no time lost) it is applied only while imaging that target. It also handles dither OK. If you then slew to another target, it starts the PPEC learning process over again so it doesn't need to keep track of the phase of the worm cycle so won't get out of step.

You can therefore use both PEC corrections together as almcl says, as the PHD2 PPEC will just correct for the errors left over after applying the Eqmod PEC.

Alan

Yes Alan, something I was not aware of, there is a whole box of toys there to have a play with, I think I will be giving the a try, I am reluctant to mess too much as guiding is fairly decent, if I could get rid of the odd blip, which in truth don't often show in star, things would be very nice.

Alan 

[Stub Mandrel]

Here are two logs:

Three hours with the 130P-DS:

 

Just for completeness, the calibration:

With the 150PL during the excellent seeing on the 25th. You can see a couple of big DEC swings, after this star quality and guiding nosedived as cloud came across:

 

Edited September 7, 2019 by Stub Mandrel

[alan potts]

I had a strange night where I tested EQmods PPEC and PHD's PPEC, alone and together and found the various different subsections of the PHD, I actually found the default normal running in PHD with EQmod's PPEC to be the best. 

Different scopes and cameras but I never went above 1 sec deflection on either RA or DEC, most of the time it was around 0.5 mark or better, in the seconds section, I don't actually know what RMS means, it did go out of these lines in Dither though. . The odd thing is even when what appears to look bad to me, I can never see it in the stars when I view the sub, so I guess not much is wrong and I am being somewhat compulsive.

Interesting to have chatted about this and something to play with more when the Moon is out and about. However the more I look at this the more I feel it comes down to quality of seeing as a few night ago without changing anything from the night before I had almost straight lines, so good in fact for a few occasions I thought it had stopped working.

Alan

[wimvb]

2 hours ago, alan potts said:

I don't actually know what RMS means

RMS stands for "root mean square", and is a standardised way of measuring average deviations. There is s ome math behind it, but I won't go into that here. In guiding, the star is kept at the same position, but it will deviate somewhat from that position. RMS is a measure of how much that deviation is, on average.

2 hours ago, alan potts said:

However the more I look at this the more I feel it comes down to quality of seeing as a few night ago without changing anything from the night before I had almost straight lines, so good in fact for a few occasions I thought it had stopped working.

This is correct. Seeing is how much a star twinkles. Due to air movement (not wind), the light from a star is deflected a tiny bit all the time. You get the same effect when you look at the moon through a high power eyepiece; craters seem to wiggle. Guiding can't keep up with these fast movements, so you set your guide camera exposure time to average out the twinkling as much as possible. That's why you need to set the guide cam exposure to several seconds. But despite this, guiding quality still depends on seeing. When you find that guiding is excellent, collect luminance. When guiding is poor, collect colour. This way you get the most out of your imaging time.

[bottletopburly]

Tried phd2 predictive pec last night ,i was impressed better than i usually get though should have  repolar aligned (semi permanent setup )

[alan potts]

I think it is time for me to learn to stop messing as generally my guiding looks better than the logs shown, maybe my occasional blip is poor balance or as we have said before seeing. I don't know if guide scope and camera affect things from the numbers point of view but, talking seconds both my RA and DEC are close to 0.5 and have even been below it a few times.

Alan

[Stub Mandrel]

Assuming you have accurate figures for guidescope focal length and guidecam pixel size, then trying to get beyond 0.5" regularly with HEQ5/EQ6 is pointless as they resolution of the steppers is the limiting factor.

My 'rule of thumb' is that a guiding RMS close to the imaging pixel size is the ideal, but even an RMS of twice that is hard to spot, especially if that's evenly spread between RA and DEC.

My 130P-DS/450D/coma corrector combo has a pixel scale of 1.83" per pixel, I have no trouble with it. The 150PL/450D is 0.89" per pixel, so I prefer to get sub-arcsecond guiding with it, although slightly worse doesn't seem to cause problems. I use a 183mm f/l guidescope with the 130P-DS and 66 ED, and a 220mm f/l guidescope with the 150PL, both with the 120MC camera.

The usual cause of trouble is when one of DEC or RA is showing spurious peaks once or twice per sub, even if the RMS is only a bit high, as this means bright stars come out as 'doubles'. Usually badly balanced DEC and sometimes solved with resist switch.

[alan potts]

25 minutes ago, Stub Mandrel said:

Assuming you have accurate figures for guidescope focal length and guidecam pixel size, then trying to get beyond 0.5" regularly with HEQ5/EQ6 is pointless as they resolution of the steppers is the limiting factor.

My 'rule of thumb' is that a guiding RMS close to the imaging pixel size is the ideal, but even an RMS of twice that is hard to spot, especially if that's evenly spread between RA and DEC.

My 130P-DS/450D/coma corrector combo has a pixel scale of 1.83" per pixel, I have no trouble with it. The 150PL/450D is 0.89" per pixel, so I prefer to get sub-arcsecond guiding with it, although slightly worse doesn't seem to cause problems. I use a 183mm f/l guidescope with the 130P-DS and 66 ED, and a 220mm f/l guidescope with the 150PL, both with the 120MC camera.

The usual cause of trouble is when one of DEC or RA is showing spurious peaks once or twice per sub, even if the RMS is only a bit high, as this means bright stars come out as 'doubles'. Usually badly balanced DEC and sometimes solved with resist switch.

My guide scope is a SW Ed 50mm, at 242mm and I have a 290mini camera. This is guiding a 638mm scope at the moment or 805mm without the reducer/flat. I have to agree even the other night when I was playing figures were around arc second most of the time and I couldn't see it int he subs at all, even at x200%, so I guess that is the acid test. I had a period the other night where this OSA (maybe got that wrong) was in red at .10, not sure whether that is good or bad but the lines were almost straight, I thought it had stopped.

Alan