  We describe the design and performance of optical elements for an x-ray beam
size monitor (xBSM), a device measuring $e^+$ and $e^-$ beam sizes in the
CESR-TA storage ring. The device can measure vertical beam sizes of
$10-100~\mu$m on a turn-by-turn, bunch-by-bunch basis at $e^\pm$ beam energies
of $\sim2-5~$GeV. X-rays produced by a hard-bend magnet pass through a single-
or multiple-slit (coded aperture) optical element onto a detector. The coded
aperture slit pattern and thickness of masking material forming that pattern
can both be tuned for optimal resolving power. We describe several such optical
elements and show how well predictions of simple models track measured
performances.
