Is this guiding OK after belt mod

[blinky]

How does my PHD guiding look folks?  Just did the belt mod, first light tonight so to speak!

 

[geoflewis]

It looks pretty good to me. RMS is well below 1” with RA and DEC pretty even so hopefully you should be getting round stars.

[blinky]

stars dont look too good to me - might be collimation though....

[geoflewis]

1 minute ago, blinky said:

stars dont look too good to me - might be collimation though....

Yes, that's not what I'd expect from the guiding stats. What scope are you using and are you guiding via a guide scope, or OAG?

[blinky]

8" F4 Newt, imaging at 1arcsec/pixel and using an OAG

[geoflewis]

2 minutes ago, blinky said:

8" F4 Newt, imaging at 1arcsec/pixel and using an OAG

Hmmm, that's definitely a head scratcher. How long are the individual exposures?

[blinky]

5min subs

[geoflewis]

Is the elongation in the same direction all over the image?

[blinky]

[blinky]

yeah

time for bed though!  Hopefully have another go tomorrow night but better hit the hay!  At least PHD guiding looks good, still seeing quite small guide corrections and RMS around 0.5

[geoflewis]

Ok, goodnight

[tooth_dr]

5 hours ago, geoflewis said:

Is the elongation in the same direction all over the image?

What would that indicate?  I’m having a similar issue when scope looks easy but is not present when scope points west post meridian flip. Is it focuser sag?

[blinky]

suppose it could be focuser sag, mine had the same symptoms before the belt mod, i tend to think ive not collimated it well enough though

[blinky]

one problem  i have is backlash in dec - cant feel it but phd is reporting it as too large and i might want to guide in Ra only! going to try and see if the belt needs a little more tension on it....

[Laurin Dave]

Given that the guiding looks good I’d suspect flexure between the OAG camera and the Imaging camera.  ZWO wobbly OAG stalk perhaps or something else a bit loose . 

[blinky]

ok, cheers - the main thing I wanted fixed was guiding due to it being night 1 of belt mod, if guiding looks good I can assume the belt is running fine then? 

[blinky]

Also, how much dec backlash is acceptable? I had it down to 609ms last night is that good?

[geoflewis]

2 hours ago, tooth_dr said:

What would that indicate?  I’m having a similar issue when scope looks easy but is not present when scope points west post meridian flip. Is it focuser sag?

Sorry, I'm not sure, but I'm thinking flexure, but that is less likely with an OAG, unless there is flexure between the OAG and imaging camera. An imaging camera gradually sagging would be one type of flexure, but that would have to be in relation to the guide camera, so it would be worth checking that everything is tight there and that the cable to the guide camera isn't too tight and straining the OAG union. I asked partly to eliminate field rotation, coma, etc. which won't give elongation in the same direction across the FOV.

[geoflewis]

2 hours ago, blinky said:

Also, how much dec backlash is acceptable? I had it down to 609ms last night is that good?

PHD2 should be able to manage 609ms backlash easily. Run the GA and accept the recommendations for backlash compensation. PHD2 will continue to monitor backlash as it guides and update the compensation based on real time feedback from guiding. Be sure NOT to have any backlash compensation set in the mount as that will throw PHD2 off.

[geoflewis]

10 hours ago, blinky said:

How does my PHD guiding look folks?  Just did the belt mod, first light tonight so to speak!

 

Looking at your original post again, the downloaded image in SGP (bright grey in the background) appears to have round stars, so what length exposure was that one? Also the period of the PHD2 graph is pretty short as I note that you're using 1s guide exposures and the graph is at only 100 guide pulses, so less than 2 minutes. Have you used PHD2 log viewer to read a much longer guide session to see if the guiding holds up over a longer period?

[Starflyer]

Guiding looks good to me Craig.

Can you try some short, say 5s exposures, that would rule out guiding errors. If you have oval stars at 5s then it's very unlikely to be your guiding.

You need to get that Concenter gadget off Gaz.

[blinky]

Will do ian, I also nipped up the screws ok the OAG tonight and Reid the cables in case that's the cause of the oval stars, does not take much at an arc sec per pixel. Also loosened the thrust bearing nut on dec and it's easier to balance the scope.  

[blinky]

OK, something is up with the newt, I assume collimation, since the stars look like they have trailing even in 5 sec subs!  So swapped over to my WO ZS73 instead..... Is anybody any good with the PHD Log files? Not sure what I should be looking for in them?

PHD2_GuideLog_2020-04-18_194624.txt

[geoflewis]

8 hours ago, blinky said:

OK, something is up with the newt, I assume collimation, since the stars look like they have trailing even in 5 sec subs!  So swapped over to my WO ZS73 instead..... Is anybody any good with the PHD Log files? Not sure what I should be looking for in them?

PHD2_GuideLog_2020-04-18_194624.txt 374.16 kB · 2 downloads

I'm no expert, but I downloaded your PHD2 log and reviewed it using Andy Galasso's PHD2 Log Viewer (available to download from https://adgsoftware.com/phd2utils/), so I'll make a few observations, but would recommend that you post your logs to the to Open PHD Guiding Google group where you will definitely get expert advice, quite possibly from Andy himself, or Bruce, or Brian - https://groups.google.com/forum/#!forum/open-phd-guiding

The things that I noticed from your log is that you had several failed attempts at calibrating with the 8" F4, with GA runs that reported errors in calibration, polar alignment and guide star focus, but there are no lengthy guide runs to see how the mount performed, just many short runs of up to ~5 minutes, many, much shorter, which really won't tell you much, if anything. As soon as your swapped to the ZS73 you got a good calibration and for the long 1h 20m guide session PHD Log Viewer reported excellent polar alignment error of 0.1', so I'm curious about the rig's configuration, e.g. is this the same mount? is the WO piggybacked on the 8" OTA or did you swap out the OTAs? If everything is mounted on the same mount and you just moved the camera from one OTA to the other then the immediately improved calibration and reported significant improvement in polar alignment is interesting, however, I did not see any new GA run after you swapped scopes.

As already mentioned, in addition to the reported poor calibration and polar alignment with the 8", the GA also made recommendations to improve guide star focus. I've never imaged with an F4 scope, but I recall reading that these fast mirror scopes may suffer from significant coma at edge of the FOV (my recollection may be wrong, so just putting my thought out there), so with the OAG prism sampling the guide star from the edge FOV I'm wondering whether this is a contributory factor. Another thought is whether everything is secure within the scope itself, i.e. primary and secondary mirrors. I used to own a Wise Optics 8.75" F4 Newt and it would never hold collimation, as the springs on the primary mirror adjusting screws were too weak, such that as soon as I moved the scope from one location to another it lost collimation (every time). It was a 2nd hand scope that I acquired in the early 1980s, which I only used for visual observing and just lived with it until about 10 years ago.....

The long guide run with the ZS73 was good, not great, with total RMS just over 1" and different rates for RA and Dec resulting in a somewhat elliptical scatter graph, which might result in non round stars. There is also a clear sin wave form in RA guiding (blue plot line) indicative of the mount's periodic error.

I'm not sure if my musings are of any help, so will repeat that the best place to go for advice is the Open PHD Guiding Google Group where the developers and other experts will be able to give you far more reliable advice. NB they will want to see your log files and probably debug files which may be uploaded to their sever from within PHD2 itself, just make sure you submit log and debug files with matching date and time stamp.

Good luck.

[blinky]

Hi,

Thanks for taking the time to look and comment - The swap to the 2nd scope is just that, comeplete removal of Newt and stick on Frac - as you say I never did another GA as I forgot.  I think I also disabled the PEC in EQMod and redid it, so it would have kicked in at somepoint in the run.  Today I removed a little more backlasg from RA and tightened the worm end ring a little more then made sure it was not binding.  Its also currently sitting tracking in RA so I can 'run in' the bearings and spread the grease about a little more...... Tonight looks good for another run!