Optical EngineeringImaging system performance based upon Fλ/d
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Imaging system performance can be described in the spatial domain, where the optical blur diameter is compared to the detector size, or in the frequency domain [modular transfer function (MTF) approach], where the optics cutoff is compared to the detector cutoff. Both comparisons provide a metric that is a function of Fλ/d, where F is the focal ratio, λ is the wavelength, and d is the detector size. Fλ/d is applied to three models: Schade's equivalent resolution (visible systems), Snyder's MTFA (MTF area; visible systems), and target acquisition (NVThermIP—an infrared system model). All models produced curves that exhibit a transition in the region 0.41<Fλ/d<1.0, representing a change from detector-limited to optics-limited performance. NVThermIP's contrast equations are simplified to easily calculate resolution and acquisition range. Trade-off analyses include range versus detector size, versus focal ratio, and versus field of view (FOV). When Fλ/d<2, no aliasing occurs. This may be important for medical imaging, where sampling artifacts may be interpreted as a medical abnormality, or for space probes, where it is impossible to obtain ground truth.