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===The lens===
[[File:Oversampled binary sensor imaging model.jpg|thumb|right|250px|Fig.1 The imaging model. The simplified architecture of a diffraction-limited imaging system. Incident light field <math>\lambda_0(x)</math> passes through an optical lens, which acts like a linear system with a diffraction-limited point spread function (PSF). The result is a smoothed light field <math>\lambda(x)</math>, which is subsequently captured by the image sensor.]]
Consider a simplified camera model shown in Fig.1. The <math>\lambda_0(x)</math> is the incoming light intensity field. By assuming that light intensities remain constant within a short exposure period, the field can be modeled as only a function of the spatial variable <math>x</math>. After passing through the optical system, the original light field <math>\lambda_0(x)</math> gets filtered by the lens, which acts like a linear system with a given impulse response. Due to imperfections (e.g., aberrations) in the lens, the impulse response, a.k.a. the [[point spread function]] (PSF) of the optical system, cannot be a Dirac delta, thus, imposing a limit on the resolution of the observable light field. However, a more fundamental physical limit is due to light [[diffraction]].<ref name="Optics">M. Born and E. Wolf, ''Principles of Optics'', 7th ed. Cambridge: Cambridge University Press, 1999</ref> As a result, even if the lens is ideal, the PSF is still unavoidably a small blurry spot. In optics, such diffraction-limited spot is often called the [[Airy disk]],<ref name="Optics"
:<math>R_a = 1.22 \, w f,</math>
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