Geometrical Optics

[jst81161]

1. The problem statement, all variables and given/known data

Explain why for a given object screen distance there are two positions where the image is in focus. Is this always true?

2. Relevant equations



3. The attempt at a solution

[berkeman]

Two positions of what, the lens? What kind of lens? What is the background for this question? What are the relevant equations?