= Solution
For a uniformly illuminated single slit of width $b$, summing the <wave amplitudes> across the slit gives the <Fraunhofer diffraction> profile
$$
I(\theta)=I(0)\left(\frac{\sin\beta}{\beta}\right)^2,\qquad \beta=\frac{\pi b\sin\theta}{\lambda}.
$$
The first minimum occurs at $\sin\theta=\lambda/b$. The <Rayleigh criterion> places one source's central maximum at the other source's first minimum; hence the slit gives $\Delta\theta\simeq\lambda/b$. A circular <aperture> instead produces an <Airy disk>, whose first minimum is at $1.22\lambda/D$. For the camera's circular <lens>,
$$
\boxed{\Delta\theta=\frac{1.22\lambda}{D}=4.88\times10^{-4}\,\mathrm{rad}=0.0280^\circ\simeq101\text{ arcseconds}.}
$$
The factor $1.22$ belongs to circular-<aperture> <diffraction>, rather than the single-slit profile.
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