The BlackGEM array wil, eventually, comprise 15 telescopes, each of 65cm diameter. The optical design gives a field-of-view of 2.7 square degrees per telescope. In this way the full array will be able to cover 40 square degrees, and be seeing limited: each telescope will be equipped with a 10500 x 10500 pixel CCD of 9 micron pixel size. With the focal length of the telescope (f/5.5) this will lead to a sky sampling of 0.56”/pix, well matched to the seeing on La Silla (~1”).
The array mode of BlackGEM is uniquely suited to match the pointing of the telescope to the shape of the gravitational wave error boxes. These are often split and elongated in shape, which makes a monolithic telescope design less suited than the BlackGEM array approach. In case of a detected counterpart, all telescopes can be pointed at the specific position (target mode), in which case the array functions as a single 3.6m telescope with a 2.7 square degree field of view. Given the fact that counterparts are expected to be fainter than the sky background (~21st magnitude/square-arcsecond) the additional read-out-noise of 15 detectors is not the limiting factor.
When completed the full array of BlackGEM cameras will be the equivalent of a 1.65 Gigapixel detector, by far the largest such a camera in Europe.
The optical and mechanical design of the telescope are completely custom-made to 
be able to provide seeing-limited image quality. The telescope structure is made from carbon fibre. The design and manufacturing of this carbon fibre structure was achieved through a partnership with Airborne (The Hague, NL) and was funded through an NWO-M project.
