...
But doing a simple sum over the whole spot taken with the canon camera, the total flux from the spot is identical to far less than a percent (or even one part per thousand) . CBP_calibration_spot_flux.ipynb. This is extraordinarily weird to me because the glass should reflect 4% of the light.
For an estimate of spot size (very, very crude - based on the above notebook, but I apparently failed at focusing even just on the fiber so take this with a grain of salt): spot size = 40 pixels (by eye this is an overestimate) * 5.25 um = 210 um. With an 800 mm lens that corresponds to an angle of .21/800 = .26 mrads. If we're 3 or 4 meters away that's (say 4): ~1mm. Huh. That is definitely not what I observed as a spot size...