Question

1-A camera uses a 200.0-mm focal length telephoto lens to take pictures from a distance of infinity to as close as 2.0 m. What are the minimum and maximum distances from the lens to the sensor?

Answer 1

The minimum distances

$\frac{1}{a}+\frac{1}{b}=\frac{1}{f}\to\frac{1}{\infin}+\frac{1}{b}=\frac{1}{0.2}\to b=0.2m$

The maximum distances

$\frac{1}{a}+\frac{1}{b}=\frac{1}{f}\to\frac{1}{2}+\frac{1}{b}=\frac{1}{0.2}\to b=0.222m$