Sharpcap Plate solves and indicates its tracking but the image is slowly drifting

[bessell61]

I was using Sharpcap to plate solve in combanation with All Sky Plate Solver for the first time. But even though it Platesolves and indicates its tracking the image is slowly drifting and thus I can't take more then 1s exposures. The location was M17 Swan nebula . Sharpcap did say Frame Orientation (00:25:47.304938): Up is 306.3 degrees east of north. Plate Solve Success (00:25:47.321915) RA=10:33:35, Dec=+89:47:17

All Sky Plate Solver is set up with the proprt information from the fits files and when plate solving directly in it the coordanates match whats in astrometry.net for coordanites.

I specified the location of the plate solving engine in Sharpcap settings as recamended. Focal langth is set to 363mm , search radious is 15degrees, star detection threshold is 42. I have attached a log and the settings export from sharpcap.

I was reading through the logs and saw a few things that are interesting but would not no best.
SharpCap attempts to get the focal length from the CPWI mount using ASCOM? Seems like an exception occurs "NotImplementedException" because the CPWI driver doesn't support reading the focal length. I'm not sure why it would look at the mount for focal length. I also noticed SharpCap searches for available plate solvers on the system All Sky Plate Solver: Found at C:\Users\aDamB\AppData\Local\Astrometry but then it references communication in the log with AstroTortilla which I don't have installed (odd). I did a test and confirmed that the plate solving test was successful. Though I see there are several indications where it seems it concludes that "Field 1 did not solve" and didn't find a matching constellation or reference.

Any assistance would be very appreciated.

Other information:

Advanced VX Mount
Celestron CPWI
Sharpcap

Bortle class 5
William Optics ZENITHSTAR 61 APO Aperture 61mm Focal Ratio F/5.9 Focal Length 360 mm
William Optics Adjustable Field Flattener 61A for Z61 Telescope # P-FLAT61A
QHY 290C Cooled Color Astronomy Camera # QHY290C Specifications:
Sensor: SONY Exmor R, IMX290 STARVIS Back-Illuminated CMOS, 1/2.8-inch
Effective Pixels: 1920 x 1080 2 megapixels
Pixel Size: 2.9um x 2.9um
Effective Area: 5.6 x 3.1mm
Shutter: Electronic Shutter
Full Well: 15ke- Typical
QE: TBD
Readout Noise: 3.2e-@low gain 0.75e-@high gain
System Gain: TBD
Unity Gain: TBD
Frame Rate (at 8-bits): 135FPS@1920x1080 220FPS@960x540 460FPS@480x270
ROI Support: Yes. Any Area ROI
Exposure Time: 50us - 1800sec
AD Sample Depth: 10-bit/12-bit (8-bit/12-bit output)
On Camera Image Buffer: Yes, 128MB DDRII Buffer
Anti-amp light control:
Cooling: 2-stage TEC, Typical -40C below ambient. Temperature Regulated
Power: USB Powered for camera and +12V powered for TEC
Anti Frost Control: Connector for removable silica gel tube
Anti Dew Control: Heated optical window
Computer Interface: USB 3.0 Super Speed
Telescope Interface: M42/0.75 & 2-inch adapter. Optional C-mount adapter
Color Wheel Port: 4-pin QHYCFW socket
Guide Port: 6-pin RJ11 Guide Port
Optic Window: AR+AR (Mono) IR+AR(Color)
Power consumption: TBD
Weight : 450g
Electrical Interface: 12V input with locking ring, USB 3.0 socket, 4-pin QHYCFW, 6-pin RJ11

[admin]

Hi,

first the things you don't have to worry about...

* Astrotortilla, ASPS and Ansvr are all pretty much the same plate solving engine with different installers. SharpCap treats them as closely related, so you may see things in the log about 'Astrotortilla' when actually you are using ASPS or Ansvr - it doesn't matter from SharpCap's point of view - the only difference between them is where it needs to look to find the 'solve-field' script that all three of them have...

* Getting the focal length (or trying to get it) from the ASCOM mount is standard. However, some mount drivers don't implement it, and SharpCap does record in the log when it encounters that situation. If you have set the focal length in SharpCap settings then that will be used. Setting the focal length is not really critical anyway - it makes plate solving *faster* when set correctly, but it will still work without it. If it is set incorrectly then it can cause problems. In any case, your log records several plate solving successes, so that all seems good.

So, the question is - why are things drifting after moving to them. This is almost certainly going to be something where the reason lies with the mount. There are a few possibilities.

1) Poor polar alignment - this tends to lead to drift in declination. I think it's unlikely as it would have to be truly terrible to limit you to 1s exposures

2) Not tracking or wrong tracking rate (ie solar/lunar not sidereal) - this will lead to drift in RA that would be fast if you are not tracking at all or slower at an incorrect rate.

3) Something slipping/moving over time. This could be any connection between pieces of hardware that could be moving slowly - check everything is tightened up properly.

Once you have done a plate solve near the target then you can use the 'Pixel Position' tool to show both the co-ordinates and the RA/Dec directions on the image, so you can see which direction the drift is happening in and whether it fits any of the categories above.

cheers,

Robin

[bessell61]

Robin,
Many thanks for the speedy reply. ‘Pixel Position' will be my next step. You are very insightful and this gives me some confidence on suspensions. This mount is not the best and can’t rule it out as the issue also. I’ll try this out and check connections. Ill also look at the alignment as well. The Siderail setting is set in cpwi. I was going to do a update also.

Best Regards,
Adam

[bessell61]

Got to play around finally last night. Thanks for the suggestions. Made sure the Alingment was as good as possible. It seemed spot on.

One problem was the cables binding I found when pointing the scope South. I temporarly fixed this and seemed to greatly reduce some of that drift but I still had some.

So I used the Pixel Position. Which worked very nice. I made sure the coordinates during plate solving matched and that was good. I did notice after watching it the movement was in the RA. Looking at this I though its almost like the mount is tracking movement too fast. So I started verifying things in CPWI. I noticed that in the newer version I updated to that under mount configuration there was now a DEC and RA Autoguider Rate so I slowly inched the speed down. I saw some improvement so I turned it down till the stars stopped trailing. It was almost perfect when done and had the Exposure at about 3 minutes.

[admin]

Hi,

good to hear that you are making progress

It's odd that the autoguider rate should be relevant here - that should only come into play when the mount receives guiding instructions, which can either be sent via the ASCOM driver by guiding software like PHD2, or via the ST4 guide cable from a guide camera (but even then software is required to tell the camera to send the signals).

Do you have an ST4 cable connected to your mount, or are you running some sort of guiding software like PHD2. If the autoguide rate is making a difference and turning it down to minimum gives the best results then it sounds like your mount may be continually making guiding adjustments in the RA direction for some reason.

cheers,

Robin

[bessell61]

I think there is a relevant point and very insightful. I was not using auto guiding on the computer and was thinking that I could probably try and disable this on the mount. Cpwi dosnt always seed alot of confidence for me but that could be me. I would probably be better off if i spent 1000s on great equipment lol. In any case.There is no ST4 but just the USB connection from the computer to the hand controller. I’ll look closer at these settings tonight,

Many thanks