Measurements requiring very high photometric dynamic range, like astronomic
al observations of faint objects near bright sources (e.g., extrasolar plan
et detection), are often limited by the scattered light characteristics of
the telescope. Although the light-gathering power of recently built telesco
pes has increased dramatically, their scattered light performance has not.
We compare models and measurements of telescope scattered light and discuss
some of the scientific and technical issues that suggest how a low scatter
ed light design could extend the scientific capabilities of moderate (4 m a
perture) telescopes.