an imaging system includes a wavelength dependent aperture stop , which transmits light with different ranges of wavelengths through apertures of different diameters . thus , different colored light will have different f - stops , which can be selected based on the power transfer and image quality requirements for the different colored light . for example , a smaller f - stop may be used with a weaker light source to produce a higher throughput for a specific range of wavelengths . accordingly , the optical system &# 39 ; s design and optimization is wavelength and f - stop dependent .