

Why the camera front is mounted  back from front end of the rails:  

The components on the
mount are actually the camera and the dewar.  The dewar is used for both
cameras.  To change the cameras, the camera is separated from the dewar (at
the place where the black part joins the white part).  The camera is then slid
away from the dewar, with the dewar position on the rails held fixed.  Once the camera
is moved forward, it is clear to be removed from the apparatus.  The extra
railing at the front of the camera is needed to allow for sliding the camera
away from the dewar.  The position of the dewar is fixed so that some settings
in preparing the spectrograph for observations do not need to be redetermined
each time the spectrograph is setup.
