  Technological advances will allow the placement of many Terahertz detectors
at the focal plane of a single telescope. For a telescope of a given diameter
and wavelength of operation, there is a limit to the number of usable detectors
imposed by diffraction and optical aberrations. These effects can be
ameliorated through an optical design where the magnification of the
telescope's secondary mirror is small and the detector package is therefore
located near the secondary mirror. A field mirror can be used to flatten the
image, and the focal reducer which matches the detector to the telescope can
also provide an image of the aperture for placement of filters and stops. A
design concept is presented for the South Pole Telescope which comprises a
10-meter diameter off-axis paraboloidal primary mirror, a Gregorian secondary
mirror, a tertiary chopper, dewar widow, Lyot stops, band-pass filter, and
space behind the focal plane for cryogenics. The telescope is bilaterally
symmetric, and all apertures are unblocked. The field of view is one degree in
diameter, so this telescope can feed an array of several tens of thousands of
detectors at Terahertz frequencies.
