Throughput calculations

Bob McMurray posting from Mark's account.

The throughput calculations performed by the IDL journal file for the various filters appears to have an error in calculating the A-omega value. The easiest way to see it is looking back up from the pixel area, where the A is a 25 micron square and the omega is the internal f10 beam. The file uses the pixel area and the externally measured angle, which is variously F18 or F16.66 or something in that range. If you use the f10 value here, and assume your FOV is filled by the blackbody, you can take the emissivity of the BB per cm^2-sr and just multiply by the conserved A-omega to get flux in photons/sec-Hz from the BB formula. This gives a factor of 3-4 more light entering the instrument, and therefore a throughput (detected electrons/photon) that is 3-4 times smaller than had been calculated. I think these numbers are in line with what we expect from the various efficiencies of the optics.