QUESTION: 
What are baffles in telescopes?

ANSWER from Chris Burrows on April 3rd,1996:
A baffle is an opaque (meaning light can't get through) barrier that stops
unwanted light from entering an optical system.  In the Hubble telescope, 
there are three principal baffles.  The telescope tube itself makes sure that 
only light from the region of the sky of interest reaches the primary mirror 
(and not earth, moon or sunlight).  There is also a baffle around the 
secondary mirror, so that stray light from the telescope tube doesn't 
reach the secondary mirror.  Finally there is a baffle that projects up 
from the center of the primary mirror, and stops unwanted light from 
getting through into the instruments.  The baffles are all painted black 
to absorb as much light as possible.