The ST-4

Since there are superior cameras and software packages for imaging at Stony Brook, the imaging software for the ST-4 will not be discussed. The tracking software is extremely important to data collection, and will be presented here. The tracking software is run from the CPU box. There are several controls including a menu that allows the operator to change parameters necessary for the tracking process. Table 2 includes a rough guide of settings for the ST-4. The exposure adjust will set the exposure time. Calibration adjust controls the period that the ST-4 moves each of the four relays during the calibration process. Each axis can be given its own time. The scintillation adjust allows for atmospheric turbulence. If the sky is turbulent when observing, this should be set at a fairly high number to track on a twinkling' star. The brightness adjust has two settings, average and faint. In the faint mode, the chip will take an average of a 3 by 3 pixel square and place the average in the center pixel. This helps find fainter stars, but will also increase the background. The hysteresis parameters can correct for backlash in the telescope's drive motor. The times are set in tenths of seconds and the ST-4 will use this time to set the motor in the correct direction before making a move. The last parameter is the gain boost. This increases the gain of the chip, but it is important to remember the background noise increases with the gain.

: Sample settings for the ST-4 guiding on a magnitude star.

Once these parameters are set, a star can be found for tracking. As stated before, a 36mm plössl eyepiece has the same focus as the ST-4. This can be used to find a star in the region of interest to guide on. If the star is slightly out of center relative to the 14", there are two sets of adjustment screws which can be moved to center the 3" telescope on the star while not moving the 14". The camera can be replaced and the find and focus can start.

Find and focus will read down the brightness of the star on a scale where 99 is overexposed, along with the coordinates on the chip. The star can be found by using the four arrow keys to move the drive motor slightly. Once the display shows high counts, the focus of the three inch can be changed until the counts reach a maximum. Before tracking with the camera, the CPU and the drive have to be calibrated. It is best to place the guide star near the position X=20, Y=80. When the calibration button is depressed, the telescope will be moved in all four directions. The CPU will determine how much time is necessary to move the telescope a certain number of pixels. Then when the star moves away from the centered position, the CPU will know how long to move the drive to get the star back in place.

After the drive is calibrated, the track button will set the ST-4 in a mode where it will track the star until it either loses track or the operator stops the track. The CPU box also contains a button to take a dark frame. If the dark frame is taken, a cover must be placed over the telescope. The ST-4 has neither a shutter, nor a vane that will block out the light.