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A Setting Up and Focusing the Spectrographs

Your instrument support person will do all the set-up of the spectrograph on the first afternoon of your run; if you've requested a grating change during your run in advance (when you fill out your Observing Run Preparation form, aka ``the pink sheet") someone will do the physical change for you, and help you do the final tweaking. The items described in this section should be carried out by trained Observing Support personnel to assure safety to our equipment. We simply summarize in this section the steps that are needed so that you will be up to speed when these steps are performed on the first afternoon.

There are basically three adjustments that need to be made when changing gratings:

  1. Tilt the grating (RC Spectrograph, GoldCam) to the desired central wavelength. (CryoCam has no such adjustment, although it is possible to vary the central wavelength slightly by selecting an offset slit.)

  2. Focus the spectrograph (compensates for different thickness blocking filters, and small wavelength-dependent focus variations).

  3. Align the spectrum on the detector (compensates for the fact that not all the gratings/grisms are perfectly square in the their cells).


next previous contents
Next: A.1 Specifying the grating tilt
Previous: 4.5 How to Observe with Multi-slits
Mar 06 1996