Chapter 44: Problem 40

Question: The focal length of a small camera is $f~=~50~{\rm mm}$, and the focal range extends from $1.2~{\rm m}$ out to $\infty$. Find the range of movement necessary between the lens and the film.

Solution: When $O~=~\infty$, $I~=~f~=~50~{\rm mm}$, and when $O~=~1.2~{\rm m}$, $I~=~52.18~{\rm mm}$. Therefore, the motion must be $2.18~{\rm mm}$.