How To Mirror Reddit?

How does a mirror have a 3-dimensional image?

• This is kind of a weird question, but let me try to explain. I did a simple experiment last night. I put one of my 35mm SLR cameras (a Minolta SRT-101) in front of the bathroom mirror. I was going to set the timer and let the camera take a picture of itself, just as a kind of joke. You know how everyone does those lame MySpace pictures in front of a bathroom mirror...well I wanted to get one with just a camera by itself. Anyway, when I was looking through the viewfinder and focusing on the reflection on the mirror, I noticed something really weird that I didn't expect at all. When I focused on the reflection of the camera, I noticed that the reflection of the background became blurry. That means that the image on the mirror has a depth of field. But how is that possible? I always assumed that the reflection in a mirror is a 2-dimensional image. Like a painting, or a tv screen or a photograph. I thought that if you took a picture of a mirror, everything would be in focus...like if you were taking a picture of a painting. If you take a picture of a painting, everything in the painting is on the same focal plane since it's a flat 2-dimensional image. And I THOUGHT that would be the same with a mirror. But since the reflection in the mirror has a depth of field, that means it's actually a 3-dimensional image. How? How can something that is a flat, 2-dimensional object still keep 3-dimensional information? I know this question is long and kind of strange. But I'm really curious about this. Does anyone have any ideas?

• Answer:

  It's because the 3D information is embodied in the _angles_ from which the light comes into the lens. Since the mirror does a fine job of reflecting not only light that hits it perpendicularly, but also light that comes at it from every possible angle, it reflects in 3D. The easiest way to envision this is to draw a top-view diagram of the mirror, camera and and object behind the camera (off to one side to get out of the camera's "shadow"). Pick two points of light emanating from the object (one on each end should suffice), and draw their angles of incidence at the camera lens after reflecting off the mirror. You'll note that to do this, those points of light are still not converged at the mirror - they don't converge until you get to the camera lens - in fact INSIDE the camera lens, where they finally converge and then flip from side to side and top to bottom. You may notice that shooting an image in the mirror is not much different than shooting through a sheet of glass. .