lower magnification is used for field acquisition.

Figure 1: Optical diagram of PISCO.

Filters (wheels FA and FB) allow selecting the desired wavelength range while neutral densities ( wheels DA and DB) are used to adjust the light level to the (generally poor) dynamic range of the photon-counting detectors (see §4). As will be explained in § 2.2, a set of Risley prisms correct for the atmospheric chromatic dispersion.

Figure 2: PISCO and photo-counting detector CP40 at the TBL.

When a field lens is selected (wheel CH), the pupil plane is located in the plane of the wheel MA, where pupil masks are available for coronagraphy (§3.3) or multi-aperture interferometry (§3.2). If low dispersion spectroscopy (§3.4) is wanted, a grism can be put into the parallel beam (wheel FA). Wavefront analysis is also possible with a Hartman sensor by selecting a microlens array in the wheel MA, and the pupil imaging mode in wheel GR.

PISCO can then be seen as an optical bench on which mounts and wheels can freely move and rotate. This concept allows a great flexibility for future instrumental developments. All instrumental functions, including wheel positioning and control of the Risley prisms are monitored by a 