Imaging Atmospheric Cherenkov Telescopes (IACTs) use large-aperture (~ 10 -
30 m) optical telescopes with arcminute angular resolution to detect TeV
gamma-rays in the atmosphere. I show that IACTs are well-suited for optical
observations of bright sources (V <= 8 - 10), because these sources are
brighter than the sky background. Their advantages are especially great on
rapid time-scales. Thus, IACTs are ideal for studying many phenomena optically,
including transiting exoplanets and the brightest gamma-ray bursts. In
principle, an IACT could achieve millimagnitude photometry of these objects
with second-long exposures. I also consider the potential for optical
spectroscopy with IACTs, finding that their poor angular resolution limits
their usefulness for high spectral resolutions, unless complex instruments are
developed. The high photon collection rate of IACTs is potentially useful for
precise polarimetry. Finally, I briefly discuss the broader possibilities of
extremely large, low resolution telescopes, including a 10" resolution
telescope and spaceborne telescopes.Comment: 10 pages, 3 figures, accepted by MNRA
