On the night of Thursday, Oct 12, 2000, we tried to use the new SBIG ST-8 CCD camera on the Meade 10-inch telescope. We'd used it once or twice before, but only to take short exposures. This time, we wanted to figure out how to activate the autoguiding feature of the camera, in which it uses short exposures on its small CCD to detect small errors in the tracking, and sends corrections to the telescope motors.
We waited for Marty Pepe's astronomy lab class to finish. Michael Richmond and Tracy Davis started setting up at 9:15 PM or so, and were joined by Marty when his class finished after 10:00 PM. Around 11:00 PM, Stacey Davis appeared to help out.
Tracy carefully adjusted the CCD camera and filter wheel so that the CCD camera body was aligned properly on the back of the telescope. See the figure below.
The figure shows the back of the telescope tube, with the forks on either side and the finder sticking out at about eleven o'clock. We placed a strip of red tape on the back of the tube, oriented roughly East-West. The dotted circle represents the mounting circle on the telescope tube, and the bold polygon the CCD camera body. Tracy mounted it so that its straight edge was parallel to the red tape, East-West.
This arrangement yields images which, when displayed with the SBIG CCDOPS software in the dome, are oriented with
South up, North down, East right, West left
Even though this is rotated by 180 degrees relative to most celestial charts, it does permit the autoguider to do a reasonable job of calibrating itself.
We discovered that the cable from the filterwheel -- which sends correction signals to the telescope motors -- must be plugged into the CCD port on the LX200 mount, not the port labelled AUX.
We ran the "autoguide calibration" procedure on a field with a single bright star (around mag 5-6?), using 2-second exposures. The first attempt failed, but a second succeeded. The calibration produced step values
It was pretty late at this point, so we tried to autoguide on only a single field: M31. We took a 90-second exposure and 300-second exposure, with no filter in both cases. The 90-second exposure showed little or no trailing -- good! All images below have been rotated by 180 degrees so that North is up and East to the left. We didn't spend a lot of time focusing the camera, so the PSF is pretty soft. The field is about 24 by 17 arcminutes.
We didn't subtract a dark frame, or flatfield, so this is a pretty grungy picture. There are a lot of hot pixels. Nonetheless, one can see some of the structure in the inner spiral arms of the galaxy. The bright stars all show a little projection to the left (East), which means that at some point, there was a brief glitch in the tracking.
Here's a closeup of the lower-left (South-eastern) corner of the image:
Here are magnitudes for the marked stars from the USNO A2.0 catalog:
star B mag R mag
------------------------------
M 17.6 15.8
N 17.9 16.2
P 17.0 15.4
Q 13.0 15.1
R 15.4 15.1
S 16.6 15.3
T (left) 17.5 16.8
T (right) 17.8 16.9
The 300-second exposure didn't come out as well; it shows quite a bit of trailing in the North-South direction. Here's a closeup of the same area from the long exposure:
We probably need to improve the alignment of the telescope, and work on tuning the autoguiding parameters, too.