The SBIG ST-4 uses the same CCD chip that is used by the
Lynxx. The ST-4 uses a CPU box as opposed to a card that must be
installed in the computer. This makes the ST-4 more portable than
the Lynxx, since it can be run by a laptop computer for imaging,
or with just the CPU box for guiding. At Mt. Stony Brook the ST-4
is used with the CPU box in the dome. The black CPU box is placed
in the dome and can be connected to the computer currently
through the 9 pin serial cable labeled ST-6. The chip is cooled
by a TEC similar to the one in the Lynxx. This cooler lowers the
temperature of the chip to approximately 20
Celsius below
ambient temperature.
The ST-4 is also capable of moving the telescope. To do
this, a relay box was built locally (for schematic diagram see
figure 1). Its purpose is to allow the CCD computer to
communicate with the telescope's drive. The relay box has
three connecting cables. The standard grounded plug is connected
to the power supply, the gray 15 pin female cable connects to the
CPU box, and the gray 6 pin male polarized cable connects to the
telescope's drive.
The telescope's drive has two speeds. The
current relay box has been designed to work with the faster speed
of the drive. To adapt the ST-4 to a different telescope, a new
relay box would have to be designed.
CCDTRACK software is available to allow the ST-4 to track using an interactive image on a computer. The difficulty with this method is the computer can only operate one CCD at a time. If the ST-4 and the Lynxx are to be run simultaneously, the computer will interactively run the Lynxx, and the ST-4 will operate through the CPU box. The CPU box contains built in tracking software. Observations requiring a second tracking computer are possible but the user is responsible for providing the second PC.
In general, the ST-4 is used solely as a tracking device. The camera head is attached to the 3" telescope. A 36mm plössl eyepiece has approximately the same focus as the ST-4 in the 3" telescope and can be used to center a star for the ST-4 to track. In the track mode, the ST-4 will chose a star to track and move the telescope via the relay box to keep the star in its field of view at approximately the same position on the chip. This makes it possible to take exposures longer than 15 seconds with the Lynxx camera. As mentioned earlier, the drive motor fails to track accurately after 15 seconds. With the ST-4 guiding the telescope, images of ten minutes and longer have been recorded. In many projects utilizing the Lynxx, the ST-4 is used to guide the telescope.