A wildlife photographer uses a moderate telephoto lens of focal length 135 mm and maximum aperture f/4.00 to photograph a bear that is 11.5 m away. Assume the wavelength is 550 nm. (a) What is the width of the smallest feature on the bear that this lens can resolve if it is opened to its maximum aperture? (b) If, to gain depth of field, the photographer stops the lens down to f/22.0, what would be the width of the smallest resolvable feature on the bear?

The resolving power of an optical instrument, also known as the limit of resolution of an object, is a property that quantifies the minimum angular separation of two objects that an instrument can resolve.

Here;

D is the aperture diameter

y is the minimum width resolved by the lens

s is the distance of the objects from the lens

$\lambda$is wavelength

The aperture is a numerical description of the size of the opening in the lens through which light can pass.

Here;

f is the focal length

D is the aperture diameter

Hence, the smallest bear feature that the lens can resolve using the maximum aperture is

The value of the diameter of the camera’s aperture

Limit of resolution;

Therefore, the data is;

Hence, the smallest bear feature that the lens can resolve using the smaller f/22.0 aperture