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
The path that light has to travel from the object to your camera was 21 feet long, 20 ft from object to mirror then 1 ft from mirror to camera. You’re trying to focus on the object, not the mirror itself, so it’s just like any other time you’re trying to focus on an object 21 feet away. The fact that there’s a mirror changing the angle of this path partway through doesn’t matter or affect anything.
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