Fast Fourier transformation of a spatial impulse response of an electro-optical imaging system provides the optical transfer function or the modulation transfer function (MTF) of the system in the spatial frequency domain. The MTFs of the subsystems in the spatial frequency domain can be multiplied to obtain the overall MTF of an imaging system. This is a much more convenient method than performing the repeated convolutions that would be required for a spatial domain analysis, and it produces a quick understanding of the performance limitations of the overall system in terms of individual subsystems in the complete system. MTF is the ability of an imaging system to faithfully image a given object. The MTF of an imaging system quantifies the ability of the system to resolve or transfer spatial frequencies. Consider a bar pattern with a cross section of each bar being a sine wave. Since the image of a sine-wave light distribution is always a sine wave, the image is always a sine wave independent of the other effects in the imaging system such as aberration. Usually, imaging systems have no difficulty reproducing a bar pattern when the bar pattern is closely spaced. However, an imaging system reaches its limit when the features of a bar pattern become closer and closer together.
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