Calibrate

Each time the TCS has been switched off, it is necessary to calibrate the collimation and index errors, and to modify the pointing model accordingly. Since the guide star zero point refers to the rotator centre, the 7-star CALIBRATE should also be done at the rotator centre. The rotator centre should be marked on the DIRECT TV monitor by a translucent ring DO NOT REMOVE.

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After doing the telescope ZEROSET and sky flats, switch on the TV and the TV and Grinnell monitors.
IMPORTANT: Check gain control is turned off before pressing the ON button. Wait about 15 seconds until the red and yellow lights go out, then turn the gain up SLOWLY in DIRECT mode (check the GRINNELL buttons), until an image appears. Always remember to back off the gain when slewing the telescope to a new object - the TV is very sensitive and can permanently damaged by over illumination. The TV has a field of approximately 9x7 arcmin.

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Move the JAG TV flat in the beam, and the TV shutter out of the beam; on lpss10 type

          SYS> tv on

and watch Mimic display.

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Start up the CALIBRATE routine

          USER> calibrate

The routine will move the telescope to 7 bright stars; you have to centre the stars on the rotator centre with the handset. Press DO each time you have centred a star. Make sure the TV scan-direction switches are pointing the right way! At the end, the routine calculates new values for the pointing offsets, and prints the RMS of the stellar positions with respect to the new model. The sky-RMS should be around 20 arcsec, which is not excellent but normal for the JKT. Note the results down in the OPERATIONS LOG BOOK, and file the calibrate plot in the corresponding folder.

You can skip a calibrate star in the sequence (for instance S19+07 which is a double star) by pressing the 'i' key.

Alternatively, you can use the command

          USER> calibrate last

to activate the previously used pointing model.