Advice needed setting up and polar aligning an AVX mount (with StarSense)

[Filroden]

I originally posed these questions in an entry in my blog detailing my experience moving from alt/az to EQ: 

Another short clear window in the early evening let me practise set up and alignment of my new AVX mount. I ran through my new alignment process, including calibrating the StarSense to the OTA. I then repeated the process and the handset reported a final PA accuracy of 30" in Dec and 3' in RA.With clouds rapidly moving over, I managed to take a sequence of 30, 60, 90, 120 and 180 second shots to test tracking. Here's the 180s (which is heavily affected by high clouds), which is consistent with the others but shows the trailing best. I did get reasonable 120s exposures the previous night, so I know it's possible (although about 40% were affected by trails).

Q1. I roughly measure the trail to be 14 pixels, or 26.6" at my pixel scale, so 0.15" per second. If correct, my maximum unguided exposure would be 13 seconds to stay within my 1.9" pixel scale. Would a PA error of 3' give this sort of trailing?

Q2. I also noticed (or believed I noticed) that the mount seems to move when tightening the mount bolt. I think that this further tightens the accessory tray which pushes on the legs more. I noticed this when I calibrated the StarSense on Betelgeuse. Normally, my goto would then be bang on centre but when I slewed back to Betelgeuse it was a little way outside my cross-hairs (using SGPro). I wonder if this is causing me problems and whether I need to attach the accessory tray at all?

Q3. I also use anti-vibration pads beneath the tripod feet. Could they also slip when adjusting the mount?

Q4. Whilst the length of trailing seemed proportionate to the exposure time, the direction was not always consistent, particularly in the shorter subs. I'm assuming this could be the affect of many things: PEC, wind, seeing. Is that right? I wonder though if I've not tightened the holding bolt/clutches enough and I'm seeing movement in the mount?

Q5. How good does a polar alignment need to be for guiding? Would it be happy with the sort of accuracy I was achieving above or would I need to drift align and improve it further? I'm hoping that a single StarSense alignment routine will get me close enough that guiding will take over (having also read that guiding seems to like an error in PA so that it only has to correct in one direction). Tune in next week for what I expect to be a frustrating first attempt

[iapa]

The controller has an All Star Polar Alignment option that you can use.

• roughly polar align
• do that after the Auto StarSense Align
• run the StarSense calibration, to let if work out the centric the camera in relation the centre of the OTA
• add some calibration stars - up to 10 can be added
• run All Star Polar Alignment - which improves the PA
• repeat previous step
• redo the StarSense alignment as you have changed the relative position of the pole

All done in less time that it took me to do PA with a polar Scope.

[Filroden]

1 hour ago, iapa said:

The controller has an All Star Polar Alignment option that you can use.

I think this is what I'm doing. My routine was:

1. Roughly align the mount with a compass
2. Set the mount to its home position
3. Check time, date and location data in handset
4. Run a StarSense auto alignment
5. Select and slew to polar alignment star (close to meridian and ecliptic)
6. Press Align to calibrate to this star, then move it into centre of cross-hairs using handset
7. Run Polar Alignment, centring star using the alt and az bolts
8. Run StarSense auto alignment once more

I chose Betelgeuse to run the ASPA and I calibrated on it before I ran the routine. I ran through steps 5 to 8 twice to refine the alignment. I wonder if I need to add more calibration stars. The manual only recommends adding one when using StarSense so I chose to calibrate first on the star I would use to run PA.

I was just expecting to not see so much trailing. I could consistently get better tracking from my alt/az mount (field rotation aside) so I expected the AVX to give me good 120s unguided exposures. That's why I'm certain I'm doing something wrong and my suspicion is I'm somehow moving the mount during the process. Maybe by not having everything tight enough or maybe not having the scope properly balanced?

With balancing, there is quite an area where I can locate the counterweight and it still hold position. The mount feels quite stiff in it's movements so the weight has to be a good few centimetres down the bar before it goes out of balance. Is there a way to improve balance?

[iapa]

1 hour ago, Filroden said:

I think this is what I'm doing. My routine was:

1. Roughly align the mount with a compass
2. Set the mount to its home position
3. Check time, date and location data in handset
4. Run a StarSense auto alignment
5. Select and slew to polar alignment star (close to meridian and ecliptic)
6. Press Align to calibrate to this star, then move it into centre of cross-hairs using handset
7. Run Polar Alignment, centring star using the alt and az bolts
8. Run StarSense auto alignment once more

I chose Betelgeuse to run the ASPA and I calibrated on it before I ran the routine. I ran through steps 5 to 8 twice to refine the alignment. I wonder if I need to add more calibration stars. The manual only recommends adding one when using StarSense so I chose to calibrate first on the star I would use to run PA.

I was just expecting to not see so much trailing. I could consistently get better tracking from my alt/az mount (field rotation aside) so I expected the AVX to give me good 120s unguided exposures. That's why I'm certain I'm doing something wrong and my suspicion is I'm somehow moving the mount during the process. Maybe by not having everything tight enough or maybe not having the scope properly balanced?

With balancing, there is quite an area where I can locate the counterweight and it still hold position. The mount feels quite stiff in it's movements so the weight has to be a good few centimetres down the bar before it goes out of balance. Is there a way to improve balance?

Have you entered lat/lon accurately and in the right order - it is one thing that catches people put.

As is 'daylight savings', that should be off in the UK just now. That can put thing just 'off'.

I have rubber feet for a washing machine under the tripod feet. One possibility is that the base you are putting the mount on may not be stable and as you move, you are putting things slightly askew? 

Re.scope balance - recommendations I have seen are the it should be East heavy, so you should probably set the 'scope to point to the target and work out if it is east or west of the meridian (east = to the right , west to the left if you are facing north behind the mount in the Northern Hemisphere - see my sig ). 

I initially ensure that everything balances then shift the weights about an inch towards the mount if the OTA is to the right, and out, if the OTA is to the left.

Which OTA of your collection are you using?

Are you still running unguided?

[Filroden]

My handset settings should be right to within a second and my go to accuracy is good after the initial calibration so I don't think it's that. (I previously made the newbie mistake of reversing my date/month the first night but that was easy to diagnose!)

I've always used anti-vibration pads and they do settle the mount very quickly. I just wanted to eliminate them as a issue. As I said in the first post, when I tighten the mount bolt after completing PA it also tightens the tripod legs because the tray is linked to the bolt. I want to test without the tray as I think the legs spreading, even slightly, will harm my PA. Though this seems a very basic design fault if true.

If you're moving your counterweight an inch with no problem then I think I'm balanced enough. I go out of balance if I move it more than an inch.

Im using the Esprit 80 so I should be well with the weight tolerance. 

I think I need to try a few things:

• use more calibration stars to improve the initial sky model
• remove the tray so I don't put pressure on the legs when tightening the mount
• make sure I've got the clutches fully locked
• check my balance and adjust the weight up/down to put it slightly heavy (in the right direction)

Are my expectations too high to get unguided exposures of 2+ minutes? If so, I probably just need to try guiding. 

[iapa]

1 hour ago, Filroden said:

I've always used anti-vibration pads and they do settle the mount very quickly. I just wanted to eliminate them as a issue. As I said in the first post, when I tighten the mount bolt after completing PA it also tightens the tripod legs because the tray is linked to the bolt. I want to test without the tray as I think the legs spreading, even slightly, will harm my PA. Though this seems a very basic design fault if true.

This is one point I am un sure of from your description, tightening the mount bolt.

You should, I believe, had the bolt that runs through the tray to the mount tight to start with - you should not need to adjust after PA etc. It may be that you do not have the mount/tripod tight enough before you start PA?

 

[Filroden]

23 minutes ago, iapa said:

This is one point I am un sure of from your description, tightening the mount bolt.

I'd seen in a couple of guides that they suggest you have to slightly untighten the bolt to get enough movement in alt and az.

If I can adjust them with the bolt fully tightened then this might be the issue.

[iapa]

2 minutes ago, Filroden said:

I'd seen in a couple of guides that they suggest you have to slightly untighten the bolt to get enough movement in alt and az.

If I can adjust them with the bolt fully tightened then this might be the issue.

Pls see PM