A Wide-Field Optical Survey Telescope: Single-Visit Depth, Etendue and Data Rate Computed from the Sky-Limited Exposure Equation

A wide-field optical survey telescope of 6.5 m effective aperture and 9.6 square degree field is designed from the sky-limited exposure equation. Its etendue is 319 square metres square degrees — the figure of merit that governs survey grasp. A 30-second visit under a 21.0 magnitude per square arcsecond sky in 0.7 arcsecond seeing reaches a five-sigma point-source depth of 24.4 magnitude in the r band, as computed from photon counting with 45 percent system throughput. At 950 visits per night the 3.2-gigapixel camera produces 12.2 terabytes of raw data nightly. The facility totals 2,900 tonnes and 900 kW. All figures are computed from the stated photometric model; the design is simulated, not measured.