'''Spectrograph focus'''
You can check the spectrograph focus on an arc image.
'''Telescope You can check the spectrograph focus'''on an arc image by clicking the "Gauss Fit" button left of centre below the image display, then clicking on arc lines across the image. The FWHM in X & Y are displayed in the information box (ideally, X=Y and is approximately constant across the field). Focus the camera by turning the knob on the camera stage in increments of a quarter turn (duck under the cryostat filling pipe inside the Coude room and locate the silver knob with vernier scale on the camera stage). Take an arc, measure the lines, move the focus and iterate.
If GIRAFFE has been used for the week before your run, you can probably assume that the telescope focus is about right. However, after an instrument change the focus might be quite far off. Good focus with GIRAFFE tends to fall in the range 1800-2100, depending on temperature. On the TCS, set the telescope focus to somewhere in this range. You can look in the scruffy A4 notebook stored in the "Log Books" section of the book shelf for a recent history of telescope focus values.
'''Telescope focus'''
If GIRAFFE has been used for the week before your run, you can probably assume that the telescope focus is about right. However, after an instrument change the focus might be quite far off. Good focus with GIRAFFE tends to fall in the range 1800-2100, depending on temperature. On the TCS, set the telescope focus to somewhere in this range. You can look in the scruffy A4 notebook stored in the "Log Books" section of the book shelf for a recent history of telescope focus values.
=='''Calibrations'''==