Fast, wide-field and distortion-free telescope with curved detectors for surveys at ultralow surface brightness.

We present the design of an all-reflective, bifolded Schmidt telescope aimed at surveys of extended astronomical objects with extremely low surface brightness. The design leads to a high image quality without any diffracting spider, a large aperture and field of view (FoV), and a small central obstruction that barely alters the point spread function (PSF). As an example, we design a high-quality, 36 cm diameter, fast (f/2.

Active Optics: stress polishing of toric mirrors for the VLT SPHERE adaptive optics system.

The manufacturing of toric mirrors for the Very Large Telescope-Spectro-Polarimetric High-Contrast Exoplanet Research instrument (SPHERE) is based on Active Optics and stress polishing. This figuring technique allows minimizing mid and high spatial frequency errors on an aspherical surface by using spherical polishing with full size tools. In order to reach the tight precision required, the manufacturing error budget is described to optimize each parameter.