  We propose a solution to the problem of astrometric and photometric
calibration of coronagraphic images with a simple optical device which, in
theory, is easy to use. Our design uses the Fraunhofer approximation of Fourier
optics. Placing a periodic grid of wires (we use a square grid) with known
width and spacing in a pupil plane in front of the occulting coronagraphic
focal plane mask produces fiducial images of the obscured star at known
locations relative to the star. We also derive the intensity of these fiducial
images in the coronagraphic image. These calibrator images can be used for
precise relative astrometry, to establish companionship of other objects in the
field of view through measurement of common proper motion or common parallax,
to determine orbits, and to observe disk structure around the star
quantitatively. The calibrator spots also have known brightness, selectable by
the coronagraph designer, permitting accurate relative photometry in the
coronagraphic image. This technique, which enables precision exoplanetary
science, is relevant to future coronagraphic instruments, and is particularly
useful for `extreme' adaptive optics and space-based coronagraphy.
