of 280Å/mm, or roughly 5.5Å/pixel. The nominal resolution of the configuration is $R=\lambda/\Delta\lambda$=230, which corresponds to roughly 20[Å]{} at 5600[Å]{}. The pixel scale of these instruments is 0.2$\arcsec$/pixel, so there is no significant degradation of the resolution due to the finite slit width.

In the initial phase of our survey, we exclusively used low resolution multiobject spectroscopy with varying integration time. This strategy maximizes the number of observed objects and provides a (nearly) full spectral coverage for every exposure. This is clearly a trade off, as we then get a significantly lower S/N spectrum for the individual objects, compared to higher resolution long-slit spectroscopy based on photometric redshifts, but the latter technique was deemed to be prohibitevely expensive in observing time in the initial phase of our project.

As our goal was to observe as many objects as possible, we used non standard order separation filters (either no filter, or the GG-375 filter, which cuts out light bluer than $\sim$3750Å). It was thus possible to cover a very wide spectral range in a single exposure (in the standard configuration the order separation filter that cuts the light blueward of 5900Å, thus the whole spectral range can only be covered in 