Guys,
Need some advice here. I have been using CCDAPv3 for 6 months and love it. I imaged several targets over the last two nights, and they were fine, but my NGC4631 galaxy keeps coming out at the bottom of the screen, on both nights. I think I have seen this a few times, but always wrote it off to poor transparency, etc. This time it seems that I am getting decent images and successful plate solves. I will post one of the images, one of the sync images, and the log in http://www.star-watcher.org/subs. I have the feeling that I am doing something stupid, but can't tell what it is.

My software versions, etc:
TheSky V6.0.0.58
CCDAP v 3.42.2
Maxim 4.60 ST8XME self guided
LX200R native focal length
Paramount ME


Initial plate solve sync image shows galaxy NEAR center, a little off. After the 'successful' plate solving and centering is done, the galaxy is then at the bottom of the screen.

I first had the problem Wed night. I did a complete new Tpoint Model rebuild on Thursday night, and the exact same thing happened, with the galaxy in exactly the same (wrong) position. Nicely repeatable, I guess, but not what I want.

I need some advice on how to figure out what is going on and what to do. BTW, I shot M66 immediatly before N4631 and it worked perfectly.

Here is some info on target acquisition and a snip from the CCDAP log:


Start with target centered in TheSky V6 6.0.0.58

NGC 4631 object information from TheSky:
Equatorial RA: 12h 42m 34s Dec: +32d 29m 29s
Equatorial 2000 RA: 12h 42m 08s Dec: +32d 32m 27s

'GET' target into CCDAP v 3.42.2 directly from TheSky:

Target becomes: 12 42 06.6 +32 31 40 PA 162.4


CCDAP LOG:

There were a few failed plate solves, etc, but the this is what happened right before the images were recorded.

03:41:08 Focus position: 1684, HFD: 4.2 arc-sec., Temp.: n/a
03:41:09 Returning to target...
03:41:09 Slewing scope...

03:41:13 Slewed to RA: 12 42 58.8, Dec: +32 25 45
03:41:13 Mount settling for 2 sec. after slew.
03:41:15 Plate solving...
03:41:15 Telescope RA: 12 42 58.8, Dec: +32 25 45
03:41:39 Z:\public\Frank\Leisure\My Pictures\Astro\SBIG-images\2008-Mar\CCDAutoPilot_SyncImages\SyncImage_NGC4631_034139.fit
03:41:41 Solved RA: 12 42 34.9, Dec: +32 28 14 PA: 160.9
03:41:41 Pointing error (arcmin): RA 0.6; Dec -0.5
03:41:41 Slewing scope...
03:41:42 Slewed to RA: 12 42 56.6, Dec: +32 26 13
03:41:42 Mount settling for 2 sec. after slew.
03:41:45 Location corrected
03:41:46 Done focusing
03:41:47 Telescope RA: 12 42 56.6, Dec: +32 26 14
03:41:48 Guide1: 44.2-6.2, -7.0-163.2
03:41:48 Getting guide star location...
03:42:09 Guider running
03:42:09 Guider x: 153.1, y: 91.4
03:42:10 Guider stopped.
03:42:10 Dither: +0.0, +0.0,
03:42:24 Guider running
03:42:32 Guide Error X: 0.0, Y: 0.5
03:42:40 Guide Error X: 0.1, Y: 0.5
03:42:41 Altitude: 65 deg.
03:42:41 Exposing...
03:49:00 Z:\public\Frank\Leisure\My Pictures\Astro\SBIG-images\2008-Mar\080307_NGC4631\L_NGC4631_01665.fit
03:49:04 Guider stopped.

Maxim reports in the FITS Header of the image:

OBJCTRA = '12 42 56.9' / Nominal Right Ascension of center of image
OBJCTDEC = '+32 26 13' / Nominal Declination of center of image
RA = '12 42 56.9'
DEC = '+32 26 13'
CENTAZ = '261.4 ' / Nominal Azimuth of center of image in deg
CENTALT = '64.0 ' / Nominal Altitude of center of image in deg
FOCUSPOS = '1684 '
ROTATOR = '179.0 '



Images and log is in http://www.star-watcher.org/subs

Thanks for any and all help you can give!

Frank Colosimo

Hi Frank,

I looked at your log files and the thing that stands out is the failure of the plate solves both on the focus star and the targets. That would be my first suggestion, find out why the plate solves are failing and correct it so the CCDAP3 always knows where it is. Also, since you are using a Paramount, I would suggest turning off the precision slew to the focus star and let the Paramount precision handle that task. I focus above 60 degrees and use Sky Star and when I slew to the focus star it is always very close to the center of the chip, if not in the center. This would save you some imaging time as well. HTH ....

Hi Frank,
Thanks for the review and suggestion. I will definitely turn off the plate solve for the focus star - didn't know that I could do that.

Did you notice that in spite of the earlier plate solve failures, that the plate solve succeeded right before the actual off-center images were taken? And it did the same thing on two separate nights?

Do you think the plate solve simply found a similar star field in a different place? Did the large galaxy confuse it in some way? I still don't know what happened, but I am confused as to why I cannot get the system to shoot this particular galaxy.

I will keep trying and see if I can learn anything that might help.

Thanks again!

Frank

Hi Frank,

One other thing I will mention is that when I did a plate solve on your image, the solve only returned 6 stars which is the minimum for CCDSoft/TheSky6. Because there are so few stars to solve with, that could be contributing to the difficulty in getting the target centered. Do you know how many stars are used when PinPoint is successful? When I do a TPoint mapping run using Automapper II, I reject any images that have less than 12 stars for plate solving. Usually I will get 70 to 80, and for me, that is plenty to produce an accurate plate solve.

Guys,
I think I made a breakthrough. I loaded a bunch of the 'offcenter' images into Maxim and tried some plate solving, and Pinpoint could NOT solve them. I can see why CCDAP could not do it!!

I played around and found that the following settings result in INSTANT plate solves on many of my problem images. I found a few SYNC images taken though clouds that were very noisy and these were not solvable, but I can understand that. Please, please - check your settings and let me know if you agree on these:

1. Must use USNO-A2.0. I had Maxim set to GSC-1.1 (corrected) and it DOES NOT WORK on any of these images.
2. Settings that helped are:
Detection Brightness: 1000
Std Dev 3.00
Max Number of Stars Used: 400

Use Stars from -200 to 20.00
Search Area as % of image: 256
Check box on Search Outward Spiral.

Now the CCDAP3 Pinpoint settings on my Setup page were: Catalog: GSC ACT Expansion: .5 I have been using 20 second Clear exposures binned 2x2
These are the defaults but the USNO seems much better, at least when using Pinpoint via MAXIM.

I will do more tests as soon as I can get out there, but I would really appreciate any advice from others who have had problems with plate solving.


Frank Colosimo

By some miracle I had a clear night, so I tried the above settings. I imaged 4 or 5 objects in a row, starting at 8 pm and finishing at 630 am. All objects were centered in the images and the run was totally successful. I noted that somehow my 30 point model from the night before was now showing a consistent offset in RA by 7 arc minutes (Dec less than an arcminute) but this is a separate issue (which I will ponder...). It was not enough to stop quick and accurate plate solves.

Hope this helps anyone else with this kind of problem. comments welcome!!

Frank Colosimo