Project overview

The Large Binocular Cameras (LBC) are two wide-field, high-throughput imaging cameras located at the Prime Focus stations of the Large Binocular Telescope.

Each LBC has a wide field of view, equivalent to 23'x23' (i.e. 1/6 of square degree), and provides images with a sampling of 0.23”/pixel, adequate to match the best seeing conditions. The optical design and the detectors are optimized in different wavelength ranges: one for UV-blue wavelengths (from 320 to 500 mm, corresponding to the UBV bands), and one for the red-IR bands (from 500 to 1000 mm, corresponding to the RIz bands). In the full binocular configuration, both channels will be available simultaneously, and will both point in the same direction of the sky, thus doubling the net efficiency of the LBT.

Side view of LBC mounted on the LBT.

The LBC optical system during lab integration in Arcetri

The two correctors are based on six lenses, with the largest having about 80 cm diameter. The third lens has an aspherical surface whereas the others have plane or spherical surfaces. Both correctors have been optimized for the relevant wavelengths: in particular, the LBC-Blue one is made of high efficiency fused silica lenses, while the LBC-Red one is made of BK7 glasses. Deformation due to mechanical stresses is not expected to compromise the optical quality of the imager which results in an 80% of encircled energy within a pixel of 0.23 arcsec both at the field center and at 15 arcmin off-axis.

A simulated deep Exposure with LBC

Each CCD array is composed of four EEV chips (2048 × 4608) to obtain an equivalent 6150 × 6650 pixel detector on each channel. The four chips are placed in a rather unconventional fashion, with the fourth one rotated 90° with respect to the others to optimally cover the corrected FOV. UV-coated, thinned EEVs for the blue channel, and IR-coated, thick EEVs for the red, have been chosen for the camera, with a very low expected fringing, which usually affects observations in the I and Gunn z bands.

Each LBC is equipped with two filter wheels, for a total of 8 filters available for each channel during the night operations.

LBC-Blue is already operational, and mounted over the first LBT mirror, and currently used to perform the telescope commissioning. LBC-Red is under integration in Italy and will be installed in the Fall 2005, when the second LBT mirror is installed.

LBC-Blue, as seen through a bent gregorian focal station, after installation at the telescope