= Rectangular-aperture dimensions from diffraction zeros
A uniformly illuminated rectangle of width $w$ and height $h$ has field proportional to $\operatorname{sinc}(q_xw/2)\operatorname{sinc}(q_yh/2)$, with angular spatial <wavenumbers> $q_x,q_y$ measured in inverse length. The first envelope zeros give $w=2\pi/|q_{x,0}|$ and $h=2\pi/|q_{y,0}|$. Two identical rectangles with horizontal centre separation $s$ introduce an additional $\cos(q_xs/2)$ factor, so the interference period is $\Delta q_x=2\pi/s$.
The factors $2\pi$ depend on using angular spatial <frequency>; axes in cycles per length would use the reciprocal widths directly. Fourier <light intensity> alone cannot determine an overall aperture translation or distinguish a mask from its inverted copy. Extra assumptions about shape and coherent illumination are necessary for a unique geometrical reconstruction.
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