Dear community,

If a user knows how well a mount performs in guiding then she or he can buy a good mount which is worth the money.

I own a cheap Skywatcher HEQ 5 Pro and I want to share the Calibration Plot which drives me mad.





With this mount I get a Total RMS" in the range from 0.95" to 3.3"

I am using the Internal Guider. In the past PHD2 refused to accept the calibration procedure.

If we can build up some kind of "database" and are able to compare the calibration plots of different mounts (modified or not) maybe we can avoid products which are not up to the task.

Please add your mount, we all need to get more information!

Clear skies!

I also have a second-hand old HEQ5.
My calibration looks better in RA but the total RMA is still about the same. On a good night with really good skies (I am in Bortle 8 ) I get total RMS around 1.

So you have a similar non perpendicular plot especially a misshaped dec-axis?
And yes indeed, the quality of the guiding depends, I think mostly on good seeing. In think that my polar alignment is quite good because I use the PoleMaster.

The author Covington writes in his book 'Digital SLR Astrophotography' that a RMS error of 0.5" is exceptional, 1" is very good, 1.5" is good and 2" is acceptable when the seeing is bad or you use a cheap setup.
But the misshaped dec-axis concerns me most. I think my mount has some severe mechanical issues, I assume a bent worm shaft. This is the reason why I am uncertain if a Skywatcher EQ6-R Pro shows a better calibration plot.

In the userguide of PHD2 they state that the axes should be perpendicular to each other. This is probably the reason why PHD2 is not able to calibrate my setup.

FWIW, I've chased a few issues in my Celestron CGX-L, and pretty much everyone I've talked to about mounts (almost all brands), has complaints! It's a favorite part of the hobby....complaining about our mounts! I've seen the CGX-L track at 0.45 rms (best), but typically tracks at 0.8 to 1.3 rms when weighted at 80% load capacity. The mount comes from the factory with 15-18 arcsecs of periodic error (which can be stomped down to 0.1 arcsec using PEC training). A couple of irritating issues is that it definitely has tracking inconsistency between different sky quadrants (not a balance issue....something else going on there). Most irritating is that it has a 21 second periodic blip of 0.6 arcsecs amplitude lasting only 0.3 seconds that can not be removed by PEC. This traces to the belt/motor interface. Finally, the mount has IMO too much DEC backlash, and definitely needs worm gear "play" adjustment between hot/cold seasons.

So, all this said, I've gotten reasonably good images from the mount as can be seen in my new AstroBin page. I attach my calibration (phd) for reference.



Cheers, Doug
www.astrobin.com/users/dmsummers/

Of course it is! Thank you for sharing, the plot seems almost perfect to me.

I will try to "admire" this part of the hobby

I get similar plots with my Orion Atlas Pro. I want to point out, though, that your plots are close to perpendicular--at least the "outgoing portion" (solid green and blue),
and the outgoing sections are what's used for calibration. I'm not sure why the DEC return portion does that odd return, but it does that for me too. My guiding is a little
better than you mention--but not that different (using the RMS in Analyze) when using GPG (dec usually < .5, RA usually .7-.9 or so) in Silicon Valley.

Here's my run from last night (7:30pm to 4:30am with a meridian flip around 10:15pm) as shown in Analyze (plotting RMS and image HFR).


You can see that, during the best parts of the night, between 11pm to 1:30am, it seemed to have an RMS in the .6 or .7 range, but later on it was pretty close to 1.0.
I assume this has to do with sky conditions more than mount, but not 100% sure. The image HFRs get worse with the worse guiding.

I don't tend to calibrate much. I've used the PHD2 advice of calibrating "well" once and then re-using the calibration, and this seems to work well
for me in KStars. (I added the capability to reuse calibrations in KStars several months ago).

Honestly, though I wish the calibration plots looked better, that weird (yellow) line is the DEC return, and my DEC guiding is quite good, I believe, so it doesn't concern me much.

Also, if you haven't noticed, if you click the options button on the Guider tab, and then click on the Calibration section, the actual angles
calculated for RA and DEC are printed, so you can see how close to 90 degrees yours are.

Hy

Hy, thank you for chiming in.

Your explanations as one of the maintaining developers of the analyze
part of the source code are very useful.

It is comforting to read that the Dec return axis of the plot does not
effect the actual guiding so much.

The charts in the Statistics section of the Analyzer Tab give a good overview. It
would be terrific if the underlying data could be further analyzed by Kstars
which could report its finding (e.g. misalignment, mechanical issues pp) back to the user.

You are right, I was not aware of the calculated angles in the
Calibration section.

Would you advise to calibrate once in a while
with the guide star standing near the intersection of the meridian and
the celestial equator and re-use this calibration?

Yes, that is the advice given by the PHD2 folks, e.g. in this slideshow , and I follow that advice in my personal imaging. Keep in mind, though, that if you rotate your camera relative to your mount, e.g. to frame your image differently, you need to re-calibrate. I don't tend to rotate my camera, I guess because I don't have a rotator so I keep my calibrations for months and it doesn't seem to hurt.

Absolutely. But what is needed are the specific analyses techniques. I'm not familiar with them. Please feel free free to contribute, or start a conversation for what analyses would be useful.

" Keep in mind, though, that if you rotate your camera relative to your mount, e.g. to frame your image differently, you need to re-calibrate."

Correct me if I'm wrong here, but I think that only applies if you rotate your guide cam. It should have no effect if you rotate your imaging camera, because whatever that sensor is seeing will not affect what the guide cam is seeing (unless you are using an OAG).


Here my calibration plot from tonight, using a CEM25P mount, so very low end, with a ZWO guide scope of only 120mm focal length and an ASI120MM-S as guide cam. I don't think one can get more basic than this.
I think calibration is pretty good and RMS of 1" is about what one can expect from the mount and the short focal length guide cam.

Jo--I agree, and yes, I use an OAG.
Hy

Here's mine. Old second-hand HEQ5 (no modifications). Orion 50 mm guide scope with ASI224MC.
RC6 reflector. 2x11lbs counterweights.

@El Corazon
@maxthebuilder

Your mounts, although being low-end, perform pretty well.
You both use SEP Multi Star (recommended) as the guiding algorithm, I suppose?
Which of the 5 SEP Profiles was chosen?

I have to recognize that your stars in the frame from your guidecams
are round. For me, this is not the case. They look like three point
shuriken. I use a ZWO ASI290MM Mini and an Omegon guidescope with an
aperture of 60 mm and a focal length of 240 mm. I wonder if this
impairs my guiding?