Guiding struggles and M27

[Ardsley Astro]

Clear night last night so even though it was a school night (That's what we call work days up north), got everything out, Aligned and tried to drop on M27. Was the most frustrating night I've probably ever had. Sharpcap platesolving suddenly stopped working so was a struggle to get on target. Had to shut the mount down and restart everything. Guiding was a nightmare. Dec backlash issues aside the RA would just swing horribly one way then swing wildly the other way. When I went to put everything away I noticed the focus ring on the mount was loose, My assumption being that was causing the guide star to drift a pixel or two cause the issue. I have some idea's to sort that but will have to wait for a clear night again.

The whole point of last night session was to see if the guiding issues were resolved rather than imaging, but of course you want to get some good images whenever you can. Out of the 20 or so subs I had tried to take with guiding I got 1 good one. I thought it a complete write off but being the belligerent chap I decided to "Stack" it with Flats and Bias frame just to see what it produced. I'm quite shocked. 

 

This is 1 60 Second sub

 

[Tomatobro]

All of us have had sessions like that, kit that worked fine when last put away then plays up when set up (usually when the clouds are due to roll in in about an hour).

Picture not bad for a single sub. 

[Ardsley Astro]

Well what a difference,  I spent some time looking over the rig and tried to resolve as many mechanical issues as I could. one of the tube ring thumb bolts was totally stripped, I'm using a Sky-Watcher 130P I picked up second hand from ebay. The thumb screw threads on the tube rings are completely stripped. Wrapped in about 50,000 wraps of PTFE tape I got them to bind properly. OTA is now properly clamped. Focus ring was an issue and this has been tightened after rechecking the focus. I rechecked the backlash on the DEC and discovered it was binding. I'm not sure why but I adjusted it again.

I didn't think I would be able to check anything based on Clear outside but risked it for a biscuit and got set up.

I first tested guiding direct through the SV705 through the main imaging scope. no major issues apart from the DEC backlash still. It might be still tight as I could hear it binding again. 

Swapped to the guide scope and SV205. No major issues at all. Using a SVBONY SV205c works fairly well. Its not ideal but it works. I took 30 subs, Did a meridian flip and set off another 90. Clouds rolled in before it could complete. Loaded into DSS I removed any dodgy guided subs and subs with satellite streaks. In all I got 74 x 60 second usable subs. (Most of these were after the meridian flip). Below is some of the PHD2 logs and a quick stretched M27.

I will attempt to do some better processing in the morning once I've grabbed some sleep.

 

 

[Ardsley Astro]

Spent a little more time processing. Tried star removal and reintegration. Any tips on processing will be greatly received. 

 

[TiffsAndAstro]

53 minutes ago, Ardsley Astro said:

Spent a little more time processing. Tried star removal and reintegration. Any tips on processing will be greatly received. 

 

looks pretty good from here

[Ardsley Astro]

1 hour ago, TiffsAndAstro said:

looks pretty good from here

Thanks, I'm pretty pleased with it.

[michael8554]

Without GuideLogs I can only speculate.

1.  The first Log Viewer image shows "ortho error = 27.6 deg"

Which may be due to a large PA error.

And measured guide rates were low and very different to the mount setting  "RA =6.1as/s, Dec = 4.3as/s"

You will get better guiding with a good Calibration.

2. Second Log Viewer image shows a smaller ortho error.

And better guide rates.

But the coarse Y axis setting on the graph means guide pulses aren't showing.

Minimum Move settings were the same on the first graph.

But Dec was much higher than RA on the second graph,   0.260 and 0.400.

 And the Min Move thresholds aren't displayed, so I can't tell if Dec was being under corrected due to the higher Min Mo.

The Star Mass isn't displayed, but the continuous "Star Lost" messages suggests that the 1 second exposure was too fast.

3.  RMS guide errors were good, but Peaks were very large.

Michael

Edited August 11 by michael8554

[Ardsley Astro]

2 hours ago, michael8554 said:

Without GuideLogs I can only speculate.

1.  The first Log Viewer image shows "ortho error = 27.6 deg"

Which may be due to a large PA error.

And measured guide rates were low and very different to the mount setting  "RA =6.1as/s, Dec = 4.3as/s"

You will get better guiding with a good Calibration.

2. Second Log Viewer image shows a smaller ortho error.

And better guide rates.

But the coarse Y axis setting on the graph means guide pulses aren't showing.

Minimum Move settings were the same on the first graph.

But Dec was much higher than RA on the second graph,   0.260 and 0.400.

 And the Min Move thresholds aren't displayed, so I can't tell if Dec was being under corrected due to the higher Min Mo.

The Star Mass isn't displayed, but the continuous "Star Lost" messages suggests that the 1 second exposure was too fast.

3.  RMS guide errors were good, but Peaks were very large.

Michael

1, Yes I don't know why the Orth angle was so high, Its the same polar alignment as the second graph. 

2, Dec was still binding a little. I'm endeavouring to get rid of that, I had adjusted it so it didn't bind but when I set everything up it bound a little again. I'm guessing with temp change. I've adjusted this again but need a clear night where I am not working the following day. I measured the Dec backlash to be around 7 seconds. I am using a SV205c planetary camera as the guide camera. its a 4k camera with tiny 1.45 pixels. It uses webcam drivers so is taking 15 frames and stacking them inside PHD to get the final guide image. The star loss was intermittent and didn't seem to affect the guiding to much. I may try a lower resolution on the camera to 1080P and set the pixel size as if its 2.9. But that pushes the imaging / guide scope ratio to 1:5.42

Once the Binding is gone, I do have the option to increase the guide speed of the DEC access only. That may help with the backlash but as this is my first goto mount (EQ-AL55i Pro) and a bit of a mystery as it hasn't been around long it's all a learning curve.

The main thing I am happy about is that I got some usable subs and ended up with a decent (for me) final image

Edited August 11 by Ardsley Astro

[michael8554]

1, Yes I don't know why the Orth angle was so high, Its the same polar alignment as the second graph. 

The second graph was better, not Good.

What was the PA error ?

2. "It uses webcam drivers so is taking 15 frames and stacking them"

Is there no ASCOM Long Exposure Driver in the Svbony driver download ? 

3. "I may try a lower resolution on the camera to 1080P".

1080P is a video mode, again, are you sure there aren't any long exposure drivers ?

4. "that pushes the imaging / guide scope ratio to 1:5.42"

Not relevant.

Your current pixel scale of 2.49arcsec/pixel with the SV205 is fine.

5. "I measured the Dec backlash to be around 7 seconds"

But the PHD2 Dec Backlash Comp is set to only 63ms ?

Is that the figure that the PHD2 Guide Assistant measured, not 7 seconds ?

Michael

 

 

[Ardsley Astro]

9 hours ago, michael8554 said:

1, Yes I don't know why the Orth angle was so high, Its the same polar alignment as the second graph. 

The second graph was better, not Good.

What was the PA error ?

2. "It uses webcam drivers so is taking 15 frames and stacking them"

Is there no ASCOM Long Exposure Driver in the Svbony driver download ? 

3. "I may try a lower resolution on the camera to 1080P".

1080P is a video mode, again, are you sure there aren't any long exposure drivers ?

4. "that pushes the imaging / guide scope ratio to 1:5.42"

Not relevant.

Your current pixel scale of 2.49arcsec/pixel with the SV205 is fine.

5. "I measured the Dec backlash to be around 7 seconds"

But the PHD2 Dec Backlash Comp is set to only 63ms ?

Is that the figure that the PHD2 Guide Assistant measured, not 7 seconds ?

Michael

 

 

Hi Michael,

1 The PA was the same for both Calibrations. I did get setup last night and after removing the slight binding of the DEC the Orth is down to less than a degree.

2, The SV205C only uses webcam drivers. Only the SV305 and above have the longer exposure driver. I am considering buying the SV305C. IMX662 sensor, It is colour but is a lot more sensitive. Its the same pixel scale as the SV705c just a smaller sensor. It will give 4.98 arcsec / pixel.

3, As above

4 Oki Doki

5, Its a rough measurement with me manually controlling in DEC at 0.5 Sidereal one direction. then reversing and timing how long before the star moves. I spoke with FLO today and they are collecting the mount to have a look at it as the backlash is excessive.

Everything will be on hold while FLO looks over the mount. 

[wimvb]

On 11/08/2024 at 12:00, Ardsley Astro said:

Dec was still binding a little. I'm endeavouring to get rid of that, I had adjusted it so it didn't bind but when I set everything up it bound a little again

As far as I know, backlash or binding can also affect the orthogonality error. Binding and backlash will differ for different pointing positions because no gear i perfectly round. If you calibrate in one part of the sky, with co siderable backlash/binding, you may get very different guiding statistics if you do the guiding in another part of the sky. The atmosphere (altitude of where your scope is pointing) will also affect the guiding. You could try recalibrating after every slew of the mount, and see if that improves the guiding behaviour.

[ollypenrice]

Don't be a slave to plate solving. It's supposed to be a convenience, which it is when it works, but M27 is not hard to find.

Olly