Finder Zeropoint in Cassegrain Mode

  This is most conveniently done after a SNAFU zeropoint determination, with the telescope still pointing to the SNAFU star, provided that star is close to the zenith. If it is not, then track a star within 2 of the zenith.

1. If not already done, select Cassegrain on the TV monitor on the Control Desk.
2. If not already there, move the telescope in order to place the test star at the reference (SNAFU) position, (the centre of the CROSS HAIR).
3. The test star must now be visible at, or very close to, the centre of the finder field. Its current position in the finder field corresponds to the reference position the the Cassegrain field.
4. Press the MENU button on the Grinnell TV Control Panel and select the `SET FINDER ZEROPOINT' option from the Grinnell Menu (see Section ).
5. Put the cursor cross upon the test star with the Grinnell joystick (on the Control Desk).
6. Press the Enter button; this sometimes has to be repeated.

The finder zeropoint is now defined, and subsequently positions indicated on the Finder TV can be translated into autoguider GDXY co-ordinates.