  The advent of extremely large telescopes will bring unprecedented
light-collecting power and spatial resolution, but it will also lead to a
significant increase in the size and complexity of focal-plane instruments. The
use of freeform mirrors could drastically reduce the number of components in
optical systems. Currently, manufacturing issues limit the common use of
freeform mirrors at short wavelengths. This article outlines the use of
freeform mirrors in astronomical instruments with a description of two
efficient freeform optical systems. A new manufacturing method is presented
which seeks to overcome the manufacturing issues through hydroforming of thin
polished substrates. A specific design of an active array is detailed, which
will compensate for residual manufacturing errors, thermoelastic deformation,
and gravity-induced errors during observations. The combined hydroformed mirror
and the active array comprise the Freeform Active Mirror Experiment, which will
produce an accurate, compact, and stable freeform optics dedicated to visible
and near-infrared observations.
