Answer
a). The minimum diameter of camera lens should be $0.587mm$
b). The resolving power is $57.14\times10^{-6}m$
Work Step by Step
a) To resolve the objects, camera lens should satisfy minimum angle of resolution condition.
So, $\theta_{min}=\frac{s}{r}$
and $\theta_{min}=\frac{1.22\times lambda}{D}$
Thus, $\frac{4\times10^{-3}}{3.5}=\frac{1.22\times550\times10^{-9}}{D}$
$D=0.587mm$
b) For resolving power of the camera lens :
$s=f\theta_{min}=\frac{1.22\times wavelength\times f}{D}=\frac{1.22\times 550\times 10^{-9}\times 50\times 10^{-3}}{587\times 10^{-6}}=
57.14\times10^{-6}m$
