Bob,

I upgraded from ACP 7.1 to 7.2a recently, the installation went without a problem. Prior to the upgrade I began shooting NGC891 and everything worked fine. Several nights ago, after the upgrade, I attempted to shoot NGC891 again with the exact same plan, but this time I started getting this message when attempting to select the guide star for autoguiding, 'Guider unexpectedly stopped while waiting for measurement'. Here is the relavent section of the log file:

02:37:17 Target is now centered.
02:37:18 (long exp(s) or requested, no orbital tracking, trying to autoguide)
02:37:18 Switching from Red to Luminance filter for imaging
02:37:28 (guide star SNR=19.5 X=463 Y=23)
02:37:28 (initial exposure interval 7)
02:37:37 (guide star SNR=21.5 X=463 Y=23)
02:37:37 (final exposure interval 7)
02:37:46 (guide star SNR=18.3 X=464 Y=22)
02:37:46 PA=333 (internal guider @ 0.0 deg)
02:37:47 **Guider unexpectedly stopped while waiting for measurement
02:37:57 (guide star SNR=17.6 X=464 Y=22)
02:37:57 (initial exposure interval 7)
02:38:06 (guide star SNR=18.2 X=465 Y=22)
02:38:06 (final exposure interval 7)
02:38:15 (guide star SNR=18.6 X=464 Y=21)
02:38:15 PA=333 (internal guider @ 0.0 deg)
02:38:16 **Guider unexpectedly stopped while waiting for measurement
02:38:26 (guide star SNR=19.9 X=465 Y=20)
02:38:26 (initial exposure interval 7)
02:38:35 (guide star SNR=19.6 X=465 Y=20)
02:38:35 (final exposure interval 7)
02:38:44 (guide star SNR=20.1 X=465 Y=20)
02:38:44 PA=333 (internal guider @ 0.0 deg)
02:38:45 **Guider unexpectedly stopped while waiting for measurement
02:38:55 (guide star SNR=18.5 X=464 Y=19)
02:38:55 (initial exposure interval 7)
02:39:04 (guide star SNR=18.6 X=464 Y=19)
02:39:04 (final exposure interval 7)
02:39:12 (guide star SNR=18.6 X=464 Y=20)
02:39:13 PA=333 (internal guider @ 0.0 deg)
02:39:14 **Guider unexpectedly stopped while waiting for measurement
02:39:15 **Autoguiding failed.
02:39:15 Doing pointing update to assure guide star on internal/OAG chip
02:39:15 Updating pointing...
02:39:15 Switching from Luminance to Red filter for pointing exposure
02:39:17 (taking 30 sec. exposure, Red filter, binning = 4)
02:39:17 (starting exposure)
02:39:54 (exposure complete and image downloaded)
02:39:55 Image finished
02:39:55 Plate-solve pointing image.
02:39:55 215 image stars found
02:39:55 373 catalog stars found
02:39:56 Solved! 129 stars matched.
02:39:56 Average residual is 0.34 arcsec.
02:39:56 Pointing error is 1.222 arcmin @ angle 91.97
02:39:56 True focal length is 1988.1 mm.
02:39:56 True binned plate scales (arcsec/pix): H = 2.24 V = 2.24
02:39:56 True image center (J2000): 02h 22m 39.6s 42 20' 47.47"
02:39:56 Imager sky position angle is 333.3 deg.
02:39:56 Rotator mech. position angle is 325.0 deg.
02:39:56 [sync] telescope synced
02:39:56 Within max error tolerance, no re-slew needed.
02:39:56 Target is now centered.
02:39:56 (autoguider still running...)

I went and then manually set the guidestar in Maxim DL and it tracked OK after that. There looked to be plenty of guide stars to pick from in the autoguider image.

Here are the specs for my equipment:

Main Camera: QSI683wsg
Autoguide Camera: SBIG ST-i monochrome
Maxim DL version: 5.23

I did see the following note on the Product Changes and Improvements section for 7.2:

6. Guide star selection now rejects saturated guide stars. Along with this, other improvements and refactoring were made. It now uses the new and improved PSF detector to find stars in the image.

Any ideas??

Thanks.

Carl Lancaster
Riverside, CT