We provide a comprehensive analysis of the space and wavelength dependence of speckle generated by a thin diffuser and imaged by a 4F optical system. The use of this space-invariant system is shown to lead to the well-known features of speckle patterns in an analytically simple and elegant manner, thereby providing a clear insight into speckle in an optical configuration that includes the Fresnel zone, the optical Fourier transform plane, and the image plane. In our analysis we assume a white-noise diffuser. The spatial variation mainly depends on the imaging system, whereas the wavelength dependence is related to diffuser heights. Motion dynamics of speckle are also included.
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