  We propose a new type of Wave Front Sensor (WFS) derived from the Pyramid WFS
(PWFS). This new WFS, called the Flattened Pyramid-WFS (FPWFS), has a reduced
Pyramid angle in order to optically overlap the four pupil images into an
unique intensity. This map is then used to derive the phase information. In
this letter this new WFS is compared to three existing WFSs, namely the PWFS,
the Modulated PWFS (MPWFS) and the Zernike WFS (ZWFS) following tests about
sensitivity, linearity range and low photon flux behavior. The FPWFS turns out
to be more linear than a modulated pyramid for the high-spatial order
aberrations but it provides an improved sensitivity compared to the
non-modulated pyramid. The noise propagation may even be as low as the ZWFS for
some given radial orders. Furthermore, the pixel arrangement being more
efficient than for the PWFS, the FPWFS seems particularly well suited for
high-contrast applications.
