Constructing a Cassegrain Telescope
This Cassegrainian telescope consists of a primary paraboloidal reflector and a secondary hyperboloidal reflector. Light reflecting from the main mirror is reshaped into a narrower beam by the secondary mirror that passes through a hole cut in the main mirror. The final eyepiece or CCD (charge-coupled device) is not shown. You can assemble and disassemble the telescope by sliding the mirrors out of the tube, changing the mirror diameter and modifying the focal lengths.