One reasonable design goal for an imaging system is to match the air disk diameter to the detector size. That insures that a significant fraction of energy in the PSF is collected by the detector. If operational constrains specify that the detector is 13 Um square and the optical focal length is 10 m, what is the necessary optical aperture diameter at a blue wavelength? At a red wavelength? At an NIR wavelength? If one optical system is to meet the design goal at all three wavelengths. What aperture diameter should be used?