next previous contents
Next: A.3 Aligning the Spectrum on the Chip
Previous: A.1 Specifying the grating tilt

A.2 Focusing the Spectrograph

In principle, one would really like to set the spectrograph collimator to a particular distance from the slit (the distance at which parallel light is formed) and focus the spectrographs by moving the camera lens. For the RC Spectrograph, the standard procedure is for the instrument specialist to focus the UV fast camera to obtain the best image of the slit, and then for the collimator to be adjusted slightly as blocking filters are inserted into or out of the beam. No external adjustment of the camera in GoldCam is possible, but fine laboratory adjustments have been made in the location of the CCD in the GoldCam camera/dewar combination so that the spectrograph collimator gives optimum images. Similarly, the distance from the camera optics to the chip is fixed in the CryoCam, and focusing is done by moving the collimator lens.

The nominal autocollimate positions are given in the table below, along with reasonable focus steps sizes.

Autocollimate Positions
Spect. Autocollimate Focus Step
RCSpec w/ normal slit 480 20
RCSpec w/ multi-slits 290 20
CryoCam 8300 200
GoldCam 500 20

Updated: 02Sep1996