Annotation

[john_robertson1953]

Hi Robin,

See attached photo, M29.

Once slewed, I plate solved and finally requested Deep Sky Image Annotation.

What are reasons why SC is slightly off in its location of M29?
The circle appears dead center, yet the star cluster is southeast of center?

What can I do to improve this?

Regards,

John

[admin]

Hi John,

I tried with that image and get a similar offset when I use the 'Plate solve and resync' button to plate solve (or the equivalent button in the mount controls), but the right position when I use 'Plate Solve Only'. I suspect the code that tries to account for the movement of the mount after the plate solve is wrong and making an adjustment that is unnecessary. I will have to check in more detail.

cheers,

Robin

[admin]

Hi John,

looking at this in more depth I realised that the effect I was seeing was down to just using your image as the camera image and the image stays the same after the 'sync' moves the mount, meaning that the results after that are not genuine.

The best bet would be if you could send me the SharpCap log from the session in question, since it will have all the relevant info in it. The other thing to do is to make sure that you have an up-to-date version of SharpCap 4.0 or 4.1 and if you use EQMOD, make sure that the EPOCH is set to 'JNOW' in the ASCOM options box (inside the EQMOD setup window). I believe that it defaults to J2000 which is plain wrong.

cheers,

Robin

[john_robertson1953]

Robin,

I believe attached is the log.

Let me know,

John

[admin]

Hi John,

unfortunately that log file cuts off just after SharpCap startup - maybe it didn't upload correctly or maybe the file on disk was already truncated.

cheers,

Robin

[john_robertson1953]

Hi Robin,

I continue to have the same problem with plate solve location. It’s slightly off center. See attached photo & log.

I’ve tried plate solve & resync, goto catalog target/co-ordinates, pixel position/click to resented, deep sky image annotation and the plate solve button on the right side. Many times it’s right on, many times slightly off centered, as per attached.

My polar alignment is fine per PHD2 as is my plate solving with ASTAP. I use Celestron Star sense which automatically aligns 4 stars. I add an additional 3 references for good measure. I guide w PHD2, and regularly calibrate with good and acceptable results with RMS .4-.8.

Please advise.

Thanks,

John

[admin]

Hi John,

something odd is happening with the mount movement when SharpCap tries to recenter the target - have a look at the figures in the log...

Code: Select all

Info   	01:15:52.670459	#1 	Field solved to RA=21:02:55,Dec=+68:13:19, field Size {Width=0.6456177, Height=0.43180907}
Info   	01:15:54.639517	#1 	Before Sync mount is at RA=21:02:03,Dec=+68:15:27											
Info   	01:15:56.461067	#1 	After Sync mount is at RA=21:01:26,Dec=+68:13:21											
Info   	01:15:56.461297	#1 	Frame center calculated at RA=21:02:36,Dec=+68:07:35 (J2000)								
Info   	01:15:56.461683	#1 	Frame center converted to JNOW : RA=21:02:55,Dec=+68:13:19									
Info   	01:15:56.462120	#1 	Plate solve info with center at RA=21:02:55,Dec=+68:13:19 recorded against mount position RA=21:01:26,Dec=+68:13:21, mapping data is 0.00011137591,0.00017400576,0.00017408887,-0.000111447196,315.65182,68.12649; {X=1562.5, Y=1044.5}; 2089; False, orientation is 57.37790113				
Debug  	01:15:56.462341	#1 	Notification (Status=OK): Mount synced to RA=21:02:55,Dec=+68:13:19, re-centering on target at RA=21:02:03,Dec=+68:15:27 (offset of 0.09 degrees)				
Info   	01:15:57.470839	#1 	Before Slew mount is at RA=21:01:26,Dec=+68:13:21											
nfo   	01:16:03.059475	#1 	After Slew mount is at RA=21:05:15,Dec=+67:27:54	

Of particular interest is that SharpCap is asking the mount to move about 0.1 degrees (third from last line) to recenter the target, but the mount co-ordinates seem to change by nearly a degree in declination (last two lines).

From that point onwards, SharpCap is trying to accound for the difference between the current mount position (dec=67:27:54) and the mount position where the plate solve happene (dec=68:13:21) and is adjusting for the offset.

Clearly the mount isn't moving nearly a degree, since it has centered the target correctly, but why is it reporting that position to SharpCap?

The two things I am thinking of here that might have something to do with that are

1) If the mount does small movements by moving away a bit and then moving back to the target. I think some Celestron mounts do that - maybe SharpCap picked up the position in the middle of the move away? Why it picked up the position then would still need explaining though.

2) Some sort of backlash compensation in the mount movement and its reporting the raw mechanical position rather than the backlash compensated position.

We do have another reading of the mount co-ordinates later in the log when you start live stacking

Code: Select all

Info   	01:19:39.607479	#36	New stack first frame processed, mount co-ordinates are RA=21:02:05,Dec=+68:14:56		

Those values are closer to the expected ones, but still not what SharpCap asked for in the GOTO. Unfortunately there's no log info to say if there were any manual mount adjustments etc in that period.

It would probably be good to keep a close eye on the mount co-ordinates and the log info about plate solving (like the above next time) to see if you can work out why the co-ordinates don't come out as expected. Another alternative would be to turn on enhanced logging of the mount communications (logging settings) which will record an awful lot of extra info in the log (mount position a couple of times a second, etc), but should have all the info needed.

cheers,

Robin