Checking and Seeing the Telescope Zeropoint (October 30, 2014 and July 16, 2015)

These instructions have been provided by Alistair for DES:

  1. At the start of the night ask the operator whether the same zeropoints as the
    previous night are installed, the "normal" zeropoints. The reason is that rebooting
    the TCS will reset them to zero, always good to check. The operator can install
    them manually.
  2. For DES, at the start of the night, point somewhere near the zenith, take an image and run the kentools center command.
    Record the offsets in the ELog. If the total offset defined as

    is greater than 10", ask the operator to apply these offset corrections to the TCS zeropoints.
    Record the TCS zeropoints in the logbook.
    Note that once observing has started there is a different spec on the pointing accuracy. See Observer2 instructions.
  3. After the correction, rerun the zeropoints to check the manual change.
  4. The above procedure is for the start of the night. Observer 2 has instructions for checking the pointing during the night. We don't normally adjust the pointing during the middle of the night except unless a problem has ocurred so that thet pointing has become bad. Observer2 instructions indicate the threshold.

Resetting the zeropoint every night is thought to be conservative, evaluation of this procedure is underway. However the operator may well ask if you want to do this, because it was part of the procedure with the old TCS. The answer is YES.

During Non-DES Observing some people might want to check on a bright star. It's always good for reassurance and in case some other observer asked for the pointing zeropoint to be somewhere other than the field center, and since it can be checked in twilight, there is no real time impact. So assuming you are pointing the telescope so the nominal zeropoint position is the focal plane center, you'll have to do an offset in order to get the star out of the gap. If you are entering an offset through SISPI, put it in with the same sign as provided by kentools.