Solar Physics 168: 229-250, 1996.
We describe an instrument we have built and installed at Mees
Solar Observatory on Haleakala, Maui, to measure polarization in narrow-band
solar images. Observations in Zeeman-sensitive photospheric lines have
been made for nearly all solar active regions since the instrument began
operations in 1992. The magnetograph includes a 28-cm aperture telescope,
a polarization modulator, a tunable Fabry-Perot filter, CCD cameras and
control electronics. Stokes spectra of a photospheric line are obtained
with 7 pm spectral resolution, one arcsecond spatial resolution over a
field 4.7 arc minutes square, and polarimetric precision of 0.1%. A complete
vector magnetogram observation can be made every eight minutes. The flexibility
of the instrument encourages diverse observations: besides active region
magnetograms we have made, for example, composite vector magnetograms of
the full solar disk, and H-alpha polarization movies of flaring regions.
During 1998 we have embarked on a set of upgrades to the instrument,
replacing the original computer system and camera controllers with modern
hardware. These upgrades will increase system reliability, and increase
the possible data rate from the instrument by roughly an order of magnitude.
New data reduction computers mean we can utilize sophisticated reduction
methods on larger datasets.