The pyramid wavefront sensor works by carrying out a Foucault test in two dimensions simultaneously. The incoming beam is first focused onto the tip of a four-sided pyramid prism, and afterwardds re-imaged onto the pupil plane. Due to the finite PSF size on the pyramid tip, the beam is split in four and four pupil images appear on the detector. Aberrations will show up as local wavefront tilts in each part of the pupil represented by a single quadruplet of pixels in the detector plane. The tilt will lead to the corresponding focal plane image contribution being moved towards one of the prism surfaces, and thus to a local brightening in the pupil image belonging to that surface. From the intensity ratio, the approximate tilt can be calculated.

F/#:100
Filters:J,H,HK,K'
Field Stops:1", 2"
#SubAP:18x18
M. Feldt, May 2007