Hubble's optical telescope assembly consists of two mirrors,
support trusses, and the focal plane structure. This system
is a Ritchey-Chretien design in which two aspheric mirrors
serve to form focused images over the largest possible
field of view.
ROLLOVER text (below left) to view light path segment on graphic (below right)
Light enters Hubble's aperture and travels down the main baffle. A baffle is a surface which eliminates stray light.
Light is reflected by the primary mirror which measures about 8 feet (2.4 meters) in diameter. Because of the concave shape, the primary mirror converges the light to the secondary mirror through a secondary baffle.
The secondary mirror, measuring about 1 foot (0.3 m) in diameter receives the light. It in turn reflects the still-converging light back toward the primary mirror through a central baffle.
The light travels through a hole in the primary mirror, to reach the focal plane, where the science instruments examine the light.