Peculiar issue of EQ5Pro + ASIair Plus GoTo working, but tracking - not

[vlex]

Hi there, 

I recently got a long Mak OTA and an EQ5 Pro and shortly thereafter got myself an ASIair Plus, asi120mm-mini and a 30f4 miniscope bundle as an upgrade. Long story short I'm not sure where to poke at this issue, but my guiding doesn't work. Here is my workflow:

• Set up the tripod and mount
• Perform PA through the mount's eyepiece
• Set up and balance the OTA with the ASIAir and the guide scope
• Power up the ASIAir from a AC power supply (the ASIAir powers the mount (12V barrel jack) and the guide camera (USB)); The comms between the ASIAir and the mount is through an USB2.0 A-B cable to the mount controller directly and it connects fine at baud 115200;
• Move the OTA to point at some bright star (ideally Polaris) and swap eyepiece with the DSLR
• Focus the OTA in preview with a bahtinov mask to ensure accurate plate solving
• Perform PA through the app (within 5")
• Choose a target and go to it. Here the first issue becomes evident - the mount goes to the desired DE/RA but then during the center confirmation it starts doing fine adjustments and usually slews continuously to the target over, and over, and over until it eventually fails, though sometimes it confirms the target had been centered so this is more of an intermittent issue.
• Go into guiding, loop, select star (if needed) and calibrate (delete older calibration data if needed). Here the second issue becomes apparent - even though ASIAir claims to be guiding, the mount doesn't move (I get star trails on exposure longer than a few seconds and the distance just grows and grows) s. video below.
  Video on Streamable (valid for 48hrs)
• Then confirm everything works again in Preview and go into Autorun where I set my lights, darks, flats, etc. And after the first image I see the star trails.

 

Theories: 

1. When I first got the setup the RA motor wasn't always moving the mount and had the seller mesh the gears better, so my first thought was that the mount might be still at fault (haven't refuted that yet). 
2. My second theory is that ASIAir doesn't talk well to the EQ5Pro over USB (as I know there's some driver issues with some of the SkyWatcher mounts). However, had that been the case I assume the GoTo wouldn't have worked either, not only the guiding. I'd like someone to confirm or deny that assumption before I spend 50 quid on a EQDir cable. I suppose I could try using ST4 (if the mount is compatible and I figure out whether I need to set anything up in ASIAir or the mount, that is..)
3. My third and last theory is that this could be because of the focal length of my OTA (1800mm) and that the rotation of the planet is just too significant at this magnification that by the time the camera (Nikon D500 whilst waiting on my OSC to arrive) takes a 1s exposure, ASIAir plate solves and confirms orientation the target had moved away, but I later refuted this theory when I took my Sigma 150-600/5-6.3 Sport set it @400mm on a vixen dovetail and got an L-bracket for the guide scope and attached it onto the body and that rendered the same result, so the length of the OTA shouldn't be the issue here.

Any suggestions and wisdom would be appreciated.

Cheers,
V

Edited January 7 by vlex
formatting

[Elp]

You PA via the air PA routine is 5 arc seconds or minutes?

[vlex]

I tune it until the last stage ASIAir thinks it's "good enough" which is within 5 arc seconds. That said, usually the total error is more like in the range of 2-3". 

[Elp]

Have you tried just using the mounts RA sidereal rate and a short focal length lens to test it's working?

A short 100mm camera lens shouldn't show much trailing at say 15-20s exposures.

[Elp]

When my air has showed trailing I've found it turns the tracking off in the mount settings by itself. The latest app version 2.0 and above with its relevant air firmwares did this a lot. I use v1.9 of the app and factory air firmwares because the latest cause so much random problems. Your issue about plate solving also happened when I used the newer softwares, my issues were worse as on the third or fourth centering iteration the mount would lose its home position and start moving the scope towards the ground into the tripod.

Edited January 7 by Elp

[Elp]

You should also calibrate above the celestial equator, example from phd2s site:

As a general guideline, it is best to calibrate within about 20 degrees of the celestial equator (declination = 0), well above the east and west horizons; and to use a calibration step size that will result in 8-14 steps in each direction.

If done right, your RA and DEC calibration graph lines should be at a perfect right angle to each other.

Edited January 7 by Elp

[vlex]

Just now, Elp said:

Have you tried just using the mounts RA sidereal rate and a short focal length lens to test it's working?

A short 100mm camera lens shouldn't show much trailing at say 15-20s exposures.

I might be a bit daft, but how does one go about using "the mounts RA sidereal rate"?

I did try a shorter focal length with my wildlife lens @400mm just to give the RPi in ASIair and the plate solver better fighting chance by increasing the FOV from less than 1 degree to more than 4. That said, perhaps I don't understand the reasoning behind your suggestion? Do you mind explaining a bit more what we're trying to prove with this?

[Elp]

That the mount is mechanically sound. You can PA via the air, then disconnect the air from the mount and use your mounts hand controller to set the sidereal motion (so the air has nothing to do with its control), and take a few test images whilst the mount is sidereal tracking. If it can't take short length exposures without trailing and you're sure the PA is fairly accurate, there may be an issue with the mount. For true PA accuracy, you should drift align, but for the purposes for this test you can PA via the air for testing consistency with how you're doing it at the moment.

[Elp]

Imaging at 1800mm isn't easy for any mount, you should be using an off axis guider at that focal length too if you're imaging dso.

Edited January 7 by Elp

[Elp]

You mentioned the mount doesn't move when guiding, can you manually slew in within the airs preview window with the N/S/E/W arrow controls?

[vlex]

Got it! I'll dig through the manual how to use the hand controller to get the mount to guide on its own, since I knew from the get go I'll be using a computer and didn't retain much of it.

I'll keep in mind the suggestion abt the off-axis guider  

2 minutes ago, Elp said:

You mentioned the mount doesn't move when guiding, can you manually slew in within the airs preview window with the N/S/E/W arrow controls?

Yes.

Edited January 7 by vlex

[Elp]

Seems like the cable connect from mount to air is working then.

Id check the mounts RA tracking on its own, 10/15/20s images at a shortish focal length shouldn't show much star trailing.

Also check when the air is connected and you've completed guiding calibration that the mounts tracking isn't switched off. Whenever I've seen my guidestars drift away on the guide camera window or star trails in the main images this was usually always the case.

But, you're guide calibrating at 120mm focal length, and your imaging focal length is 1800mm, I'm guessing this is also causing and issue. If you can imagine it, if you're looking at someone far far off in the distance with your own eyes and they step side to side, you may not see the motion, but looking through binoculars or a scope you'll see it, it's a similar principle when your optics aren't matched, you don't have to match FLs exactly, it's more to do with pixel scale which ive never read into, but I know from experience when I switch to my OAG, the guiding is much better, and when imaging with my C6 at 1000mm, my 120mm guidescope doesn't cut it.