  Modern observatories and instruments require optics fabricated at larger
sizes with more stringent performance requirements. The Daniel K. Inouye Solar
Telescope will be the world's largest solar telescope at 4.0 m aperture
delivering a 300 Watt beam and a 5 arc-minute field. Spatial variation of
retardance is a limitation to calibration of the full field. Three polarimeters
operate seven cameras simultaneously in narrow bandpasses from 380 nm to 1800
nm. The DKIST polarization calibration optics must be 120 mm in diameter at
Gregorian focus to pass the beam and operate under high heat load, UV flux and
environmental variability. Similar constraints apply to the instrument
modulators with large beams near focal planes at F/18 to F/62. We assess how
design factors can produce more spatial and spectral errors simulating
elliptical retardance caused by polishing errors. We measure over 5deg circular
retardance and spectral oscillations over +-2 for optics specified as strictly
linear retarders. Spatial variations on scales larger than 10 mm contain 90% of
the variation. Different designs can be a factor of 2 more sensitive to
polishing errors with dissimilar spatial distributions even when using
identical retardance bias values and materials. The calibration for the on axis
beam is not impacted once circular retardance is included. Calibration of the
full field is limited by spatial retardance variation unless techniques account
for this variation. We show calibration retarder variation at amplitudes of
1deg retardance for field angles greater than roughly one arc minute for both
quartz and MgF_2 retarders at visible wavelengths with significant variation
between the three DKIST calibration retarders. We present polishing error maps
to inform new calibration techniques attempting to deliver absolute accuracy of
system calibration below effective cross-talk levels of 1deg retardance.
