  We present here the Calar Alto Schmidt-Lemaitre Telescope (CASTLE) concept, a
technology demonstrator for curved detectors, that will be installed at the
Calar Alto Observatory (Spain). This telescope has a wide field of view
(2.36x1.56 deg^2) and a design, optimised to generate a Point Spread Function
with very low level wings and reduced ghost features, which makes it
considerably less susceptible to several systematic effects usually affecting
similar systems. These characteristics are particularly suited to study the low
surface brightness Universe. CASTLE will be able to reach surface brightness
orders of magnitude fainter than the sky background level and observe the
extremely extended and faint features around galaxies such as tidal features,
stellar halos, intra-cluster light, etc. CASTLE will also be used to search and
detect astrophysical transients such as gamma ray bursts (GRB), gravitational
wave optical counterparts, neutrino counterparts, etc. This will increase the
number of precisely localized GRBs from 20% to 60% (in the case of Fermi/GMB
GRBs).
