Question

If camera A has $f4.5$ lens and camera B has $f2.8$ lens, and the diameters of both the lenses are equal, then.

• A. A is better for photographing fast moving objects
• B. Pictures taken by B will always be sharper
• C. Pictures taken by A will always be shaper
• D. B is better for photographing fast moving objects

Answer 1

Answer: (C)

Pictures taken by A will always be shaper

$\begin{array}{c}\text{Given}\\ \text{Numerical Aperture of lens}A=f/4.5\\ \text{Numerical Aperture of lens}B=f/2.8\\ \text{where}f=\text{focal length}\\ \text{A lens with larger numerical aperture}\\ \text{will form less sharper image.}\\ \text{Here numerical aperture of}A\text{is less than}\\ \text{B ( since}f\text{is constant)}\\ \text{so pictures taken by A will always}\\ \text{be shaper.}\\ \text{option}C\text{is correct.}\end{array}$