proposed a slit spectroscopy setup which allows a high spectral resolution and a fixed spectral calibration. This is the option we chose because we wanted to be able to do stellar classification of the components of binary stars and work with a good spectral calibration. The main drawback is a loss of sensitivity due to a rejection of the light by the entrance slit. PISCO can be easily converted to a spectrograph by selecting the grism in the wheel FA and a slit in the wheel EN in the entrance image plane (I1) (Fig. ). It then provides a low dispersion spectrographic mode with a spectral range of 350–500 nm, and a spectral resolution of $\sim$300 with a slit of 0.7. This range was chosen to allow stellar classification of close binaries with the hydrogen Balmer series. Unfortunately, the atmospheric turbulence is stronger in the blue domain, which make images more difficult to restore. The wavelength calibration can be performed with calibration spectral lamps in wheel AS (Halogen, Argon, Neon and Xenon lamps).

Quick switching between imaging and spectroscopy is possible since this mode can be remotely selected by rotating the wheels. The observing procedure is the following:

– obtain 