Modern telescopes need to have their instruments attended to before most nights - in this case, the dewar that keeps the Mosaic detectors cold to reduce background noise must be filled. Dave the Observing Assistant who runs the telescope all night is at far left on the orange platform and the telescope is pointed low so that he can get at the dewar. The black cylinder is the secondary mirror support for the Cassegrain focus and is also the "Prime Focus" cage. The Mosaic detectors are mounted at Prime focus with the mirror removed from the bottom of the cage. In the old days, the observer would ride inside the prime focus cage all night, guiding on a field star to get one of those spectacular photos you probably remember from your grade school science class. This image was taken with my 10mm fisheye lens with an exposure of 1/15 seconds at f/3.2, ISO 400.
Here's another view of the KPNO 4-m Mayall telescope, taken from the northwest side of the telescope shortly after the louvers on the west side were opened. This image was taken with my 10mm fisheye lens with an exposure of 5 seconds at f/8, ISO 100.
Guess where I am tonight - Ok, the photo gives it away. I am at the Kitt Peak 4 meter Mayall telescope learning how to use the Mosaic camera for a Target of Opportunity observing program this spring involving WISE spacecraft discoveries. This image was taken in twilight as the telescope was being prepared for the night. Unfortunately, the humidity has closed us down for the time being, but it's fun to type this from the control room next to the telescope. This image was taken with my 10mm fisheye lens with an exposure of 1/10 seconds at f/2.8, ISO 400.