We describe the multislit spectrograph “SFM”. It is designed to obtain simultaneously spectrograms of faint objects over a field of 10 arcminutes for an entrance aperture ratio f/10, or of 15 arcmin for f/8. The SFM makes the dispersed image of the entrance slits directly, without any fiber optics. The number of entrance slits can be as large as a few hundreds, depending on the distribution of the sources on the sky and on the wavelength range. The present reciprocal dispersion is 79Amm−1 in the wavelength range 3600 – 6400A. The SFM is expected to reachmv≈22 with a signal to noise ratio of 10 for a spectral resolution of 3.3A and an integration time of 5 hours, when used with the photon counting detector CP40.