Design for an angular separation before choosing magnification

Two comparable mutually incoherent point sources are 6.0 mm apart transverse to the line of sight at a range of 1.0 km. Observation uses 600 nm light and a clear circular aperture.

What minimum aperture diameter meets the ideal Rayleigh criterion?

Organize the givens & assumptions

Source separation = 6.0 mm
Range = 1.0 km
λ = 600 nm

Two comparable mutually incoherent distant point sources; monochromatic light, clear uniformly illuminated circular pupil, diffraction-limited imaging, adequate sampling, and the conventional Rayleigh criterion.

A $0.122\ \mathrm m$
B $0.061\ \mathrm m$
C $0.244\ \mathrm m$
D $0.100\ \mathrm m$

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