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The change from IDS to FOS (or vice versa) is an operation for the duty technician or the support astronomer. If the FOS cryostat has been pumped down and cooled, the changeover time is less than half an hour. It must be made plain that if you want to use FOS when it has not been scheduled, the technical staff must have been notified via the support astronomer. The cryostat takes some hours to pump down to a reasonable vaccuum, and to cool to its operating temperature (150 degrees K), so more than a days warning is needed.
The change from IDS to FOS involves:
a) Switching the IDS detector to a safe condition
b) Removing the folding prism which was sending light to the IDS detector so that the light can enter FOS via the flat mirror.
c) Inserting a light tight tube between the IDS and FOS.
d) Changing the dekker and below slit filter slides with those specifically for FOS.
e) the camera electronics must be switched on. This involves a cable change at the Cassegrain cabinet, so the RGO CCD camera controller can drive FOS.
f) Finally the software must be re-initialised by restarting ADAM and selecting the FOS mode at the observer's console.