Microscopes are used to look at small objects that are close to you, and telescopes are used to

look at small objects that are far away from you.

The bacterium E$.$ Coli measures $1$ micron across. What minimum numerical aperture is

required to resolve a single bacterium? $($hint: to resolve an object, the blur circle diameter

is at most $0\mathrm{.}5$ x the size of the object$)$

It is thought that a space$-$based surveillance telescope $(200$ km altitude$)$ can resolve

grapefruit$-$sized objects on the Earth's surface. What is the required diameter of the

telescope?

Assume the size of grapefruit to be $10$ cm