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
An interesting comparison can be made with rear view mirrors in cars. When glancing at your mirrors, the focus point is roughly the same as that through the windscreen, so your eyes do not have to re-focus. However, a number of modern cars now have camera based mirrors. When looking at those, the eye is required to focus on the actual screen itself, requiring the eye to re-focus, which takes a small amount of time.
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