[填空题]
Spy planes fly at exb+s(86e as fgytremely high altitudes (25 ; xdvi. p3mg.,*8k8aj6 qhfeqwpv 7jx$km$) to avoid interception. Their cameras are reportedly able to discern features as small as 5 $cm$. What must be the minimum aperture of the camera lens to afford this resolution? (Use $\lambda=550\mathrm{~nm}.$)D = cm
