So I was taking a photo of the reflection of an exit sign. The sign was about 20ft away. I was shooting the screen of a phone which was about 1 foot away. In order for the sign in the reflection to be in focus, I had to set the focus to about 20ft even though the reflection I was shooting a phone screen that was a foot away. The phone and table it was sitting on were very out of focus including the screen, but the reflection of the sign was crystal clear. Why?
In: Physics
Physically, there is no difference between a perfect mirror, reflecting an object behind you, and a transparent pane of glass through which you see an object in front of you. In both cases, the light had to travel the same distance, and arrives at the same angle, so the optical equations are exactly the same.
As a result, even though the *mirror surface* is only a foot away, the *light* from the object you are examining moves and behaves exactly as though it is as far away from the phone as though it were “really” on the other side of the mirror.
This fact, that you can pretend that reflections are actually mirror-side real things, is used in math and physics to simplify the solution to complex differential equations it is called the “method of images.” Quite useful.
Latest Answers