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To take a calibration frame you will need to move the A&G mirror so that light from the calibration unit is directed into the spectrograph, and then turn on one of the comparison lamps. You may wish to select one of the filters in the calibration unit filter wheels. A typical command sequence might be as follows:
If you require a very uniform illumination, you should use one of the diffusers in the calibration unit. Ask your support astronomer to select this. This should not normally be necessary, and it is normally much more efficient to observe without the diffuser.
To take a calibration frame, use the most appropriate of the following commands: FLAT, SKY, ARC, MAP, DARK, BIAS and FLASH. The first four of these commands ( FLAT, SKY, ARC, MAP) differ only from the RUN command discussed above in that a different observation type is written to the header, in order that data-reduction software can recognise calibration exposures and process them accordingly. The DARK command carries out an exposure of the specified length, but without opening the CCD shutter, whilst the BIAS and PREFLASH commands carry out zero length exposures.
It is possible to take multiple exposures using one of the following commands: MULTFLAT, MULTSKY, MULTARC, MULTMAP, MULTDARK, MULTBIAS and MULTFLASH.