Field vignetting

• If there is evidence of vignetting on CCD frames, suspect that the filter wheel has lost its encoder position, probably because it's become loose. There are notes on how to check the status of the main CCD and autoguider filters in the JKT Quality Control folder in the control room. In the first instance though it's probably easier to go and check the filter wheel, and make sure that it's located securely, with the white clamp underneath, hand-tight. You must do a ZEROSET MAINFILT from the ICS to initialise the filter wheel afterwards.
• The drift table may have moved