Hello everyone,   I passed this situation by George, but he does not use PHD2 guiding and really had no answers.   Recently I received my second or actually third AP mount.   I sold my 900 and upgraded to the 1100 which is scheduled to be my portable mount.   I wish I would have kept the 900, but CFO would not allow it.


Anyways, In short, on a side by side comparison, my new 1100 does not seem to track that well.   Gasp.   I know it is something I am doing wrong.   My 1600 in the observatory is an absolute work of art.  The other night I had the RMS down to about 0.27.  Amazing.  The 1100 tracking was good but not as good as the observatory.  I am trying to figure out what is going on since my 900 tracked better than my 1100.  Here are some things I have done.

Yes, I am accurately polar aligned.
Yes, there are no cables caught up and so on and so forth.
Yes, I calibrate PHD2 near the meridian and just at about a dec of 0.
Yes, my scope is accurately described in PH2 (922mm focal length)
Yes, PHD2 is reading the camera pixel size correctly.
I have a rudimentary model established and pointing is excellent.
I have a good PEC installed and with PEC enabled the error is about 1 arc-sec.  Without it is about 3.2 arc-sec.
The guiding is being done with a separate guide camera on an OAG.  The scopes are a Newtonian reflector (home built) and a hyperbolic Newtonian reflector (takE130D).

I have tried to guide with and without the model and the PEC and the guiding is kind of worse without those two tools enabled.  Not sure on that.

What I seem to see is that when calibrating PHD2 does it's standard thing.  Moves in RA first in one direction (at least I think this is correct, please confirm gang), then moves in RA in the other direction (or stops guiding until the star returns to the original position, please confirm gang).  In DEC (which I think is the second set of movements, please confirm) it moves in one direction in about five or six steps and them moves back in to the original position in five or six steps.

The problem I see in the above paragraph is that when doing the first set of movements which I think are in RA, you can see the five or six steps in one direction, BUT IN THE OPPOSITE DIRECTION I only detect one step.  The star moves right back almost in an instant.   Not sure what is going on with this.  The last sentence is with the exposure at say 3 second.  WHen I move the exposure to 1 seconds, I can see five or six steps in one direction and two in the other while the star returns to the original position.  I have never seen this happen.  I always detect several steps in each direction.  It seems like there is some sort of backlash or something in the second of the four sequenced star movements PHD2 accomplishes in order to properly calibrate.

I think I have a well balanced setup and for a total disclosure I run a two scope array utilizing a side by side arrangement.  The observatory has the same thing.  I think there is an issue in RA.  This seems to be where the most corrections happen and this is expected with good polar alignment.

A somewhat on topic question is what are people using for the exposure during calibration?  1 second or the expected exposure during actual guiding which for me has generally been between 4 and 8 seconds.

Has anyone else seen this?  George said that there is a backstop adjustment in the new boxes.  However, I trust that the gang at AP has sent this thing out in almost perfect condition.  Not perfect, because as humans we are not perfect for sure. 

Anyways any suggestions?

Thanks in advance for any help. 

If you post a log then we might notice something that's amiss.

When calibrating with PHD on all my mounts I just the same cadence that I use when guiding but I don't think that it matters much as long as the calibration star generates plenty of signal.

Have you tried using Multi-Star. That was a godsend for me when imaging in my backyard when seeing was poor.

When PHD calibrates it moves the step size until (default from memory) it reaches 25 arc seconds but the step back to zero uses MaxMove instead. So, that's why the reverse direction looks quite different.

Rgrds-Ross

Thanks Ross,

I really appreciate any responses.  The cadence is the correct term.  Do you know if PHD2 calibrates in RA first?  I am almost sure it does. 

If so, the first cadence of movements is just like I am used to.  I think the mount pushes to the west faster than sidereal to test the tracking signal.   The second step, which I thought is the stop tracking until the star goes back to the original position is what looks pretty darn weird.  You are indicating that it is using the MaxMove instead.  So I stand corrected.

Yes, I use the multi star tracking.

My seeing was spectacular the past couple of nights down here in SW Florida as evidenced by the performance of the 1600 mount in the observatory.

Joel,

Thank you for the commentary.  That is really helpful.  A while back ago pursuant to recommendations from Roland, I canned trying to use the backlash setting.  Thanks again for the support.

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As mentioned, logs will help a lot. 

The last few nights have been all over the place for me guiding.  Seeing has been pretty bad, especially down lower to the horizon (I usually start at 25-30d), and then decent in the middle of the night, notably higher.  Bad like guiding around 0.4" with periodic peaks to 0.7" or so, good like 0.2x" other times.  Last night was worse because of wind, so even when seeing improved I had a fair number of excursions from wind blowing.  I mention this because we are close enough together it might be similar.  Make sure you aren't just fighting a bad night.

I often calibrate at 1s just from impatience, and seem to get a good calibration.  I also often just use the regular exposure if I'm doing it in a sequence.  I can't see any real difference between the two.  My guiding is in the 3-5s range usually. I do have encoders so going much longer also works for me, but I do not because of wind.

You might want to separate using a model from guiding at first, just to eliminate one possible source of problem or misconfiguration.  Though that seems unlikely.  But I have managed to screw up models and make it worse. 

Backstop:  Mine came from AP with enough play if you push on the bottom of the motor box (toward the mount body) it moves very slightly, maybe 1/2mm and it takes only slight pressure to move it.  I don't know if that's correct, but mine works and both are the same.

A guiding assistant run inside the log would be helpful of course. 

We should meet at big cyprus with them and compare notes sometime.  Though now the clouds seem to be coming back.  Though a tandem rig doesn't sound very portable? 

Anyway, nearby (sort of) if I can help.

Linwood

Thanks everyone.   Yes, Lynwood a trip to Big Cypress is soon upcoming.  I am still working out the bugs.  My homemade Newtonian has issues with the diffraction spikes being doubled up on three of the vanes, which I am thinking means that the vanes are not completely parallel to the incoming light.  In addition, I still don't seem to have the spacing right.  What a pain.  Even a simple Newtonian is not an easy build at least for me.  I am going to take it off and replace the spot on the tandem rig with my poor man's 130GTX, an ES 127ED FCD100 with an AP27TVPH.  Hopefully Roland will make me a 130 this next run and my name comes up and I can sell the ES.  Anyways, this will make the rig much more portable.

Last night, I deployed the two scopes in the observatory and the 1600 guiding was once again good.  However, I did find a mistake in my settings which showed guiding better than it actually was.   I tweaked the distance between the APTVPH and the chip on my 12" GSO RC to eeek out a little more speed and reduction and failed to change it on my AP drivers and my PHD2 Settings.  I went from a fl of 2000 to a fl of 1900.  So the readings were a little better than was actually happening.  The issue is now fixed.

Then, I found an issue with my OAG on my 1100 dual tandem rig.   My focus for the OAG was not good to say the least.  I had not realized this.   I could not rack in the focuser sufficiently to achieve excellent focus.  I was off quite a bit and could not notice it until I started to really drill down.   I fixed everything by pulling the OAG forward and adding a spacer behind it.   I was able to achieve excellent focus.  Guide readings improved as expected.

The two tweaks resulted in readings that are very close to each other on the two rigs all things considered.

I don't know what it is about my brain, but I can't seem to discern good seeing from marginal to bad seeing.  I reported good seeing, but that was because my settings on the 12" GSO associated with my PHD2 guiding on an OAG was not correct.   Seeing was okay last night.  The wind died down as you know.

Anyways, I am a little less anxious about my 1100 "tracking" issue.  It is probably not an issue at all.  I think the fixing the two errors in my setups resulted in converging readings for both of my mounts that point to the excellent racking I am used to from my ap mounts.  I was able to get the second night of data on M33 in the observatory and killed the 1100 imaging due to the issue with the Newt.  Tonight I will switch out the newt and try imaging with both rigs, weather permitting.  I am going after those beautiful clusters Dean just imaged centered around NGC 633.  I have imaged those before and want to go back.  What a beautiful field.  

On Wed, Oct 26, 2022 at 11:02 AM, Emilio J. Robau, P.E. wrote:

Yes, Lynwood a trip to Big Cypress is soon upcoming.  I am still working out the bugs. 
....
Then, I found an issue with my OAG on my 1100 dual tandem rig.   My focus for the OAG was not good to say the least.  I had not realized this. 

Last night for me the clouds were a problem early, then pretty good, but wind had an impact.  I went from 0.15 or so at one point up to 0.4.  At least I think it was wind, though I monitor wind about 8' from the OTA and there was only a loose correlation at best with what I was seeing.  

Interesting comment on focus and the OAG.  I've found the OAG train from ZWO (OAG-L, EFW, ASI camera) yields focus VERY close to the bottom of the focuser draw tube.  I have about 2mm travel left.  I'm getting a Photon Cage which I think may improve this (more space to the sensor, closer overall focus, raised guide camera -- hope I'm thinking right). But there's little room to spare there.  I had been told many times that guide focus does not matter much - I'm convinced they are just wrong.  I get significantly better results if I cut the guide HFD in half (which is easy to do, it takes just a tiny amount of change, at least on my refractors).  Makes me rethink thinking that those with electronic focusers on their guide camera were over-kill (also makes me think that filter offsets would be useful there for filter changes). 

Speaking of guiding, there's a neat feature of NINA that I find quite interesting, and to some extent dispels the idea that once you are guiding well below your imaging scale improvement does not matter.  This is a plot of HFR (a somewhat reasonable estimate proportional to FWHM) against PHD2 RMS error (on the right scale).  One can argue cause and effect (and whether HFR of 2.2 is substantially better than 2.5) but there's a strong correlation here.   My (main) image scale is 0.64"/pix, so by most measures my guiding was good all the time, but there's a substantial improvement in the stars as guiding improves.   Cause or effect?  One night I'm going to screw up my PHD2 parameters and make it a bit worse on purpose (with same seeing) and see what happens; I'm betting HFR follows. 

But for NINA users bored watching it run, it's an interesting thing you can display live (not historic though, only current session; to get it just use the drop down where in this shot is "rms"). 



I'm seriously thinking of heading to Big Cypress tonight.  I'll probably wimp out, still haven't figured if I have everything I need to pack up the new OTA, but I have to at some point.  Sure you don't want to make a first run at it while the moon is (almost) new?  :) 

Linwood
 

I wanted to cap off this thread.  Lat night I established my horizon limits.  I ran a new model for my 1100 tandem rig with 78 points.   I had no plate solve failures.  Focus on the OAG was achieved with great accuracy.  I aligned my home made Newtonian secondary vanes.  I recollimated the scope.   I re-calibrated utilizing a one second cadence.  I used the guiding assistant to establish the min move values.   I did not do anything with backlash.  The results were astonishing.   The mount RMS was at 0.23 to 0.35.  The tracking was as good as it gets.

I am thrilled to have another perfect AP mount.  Congratulations to AP for continuing to produce the world's finest German Equatorial Mounts.

Sorry for the ask, do you have encoders?
Im a new owner to be, this would be my second mount, my first is a 10 micron. I don’t want to go into shock with above .3 Guiding.