How does a mirror have a 3-dimensional image?

Question

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 1

That is a good observation. The reason everything in a painting will be in focus on a painting is because it begins as a 2D image. That is, it was painted on a plane, which means that the light you see from the picture is spreading out from the same distance.

When you look in the mirror, however, it doesn't begin as a 2D image. Instead what you see is the reflection of the 3D objects behind you, which means the light enters your eye as if it had been spreading out from the objects, if they were an equal distance behind the mirror (this is one of the basic properties of a mirror, the reflected rays leave the plane at the same angle they strike at, meaning it is geometrically no different from looking through a window). This why the camera went out of focus... the objects you see are (counter-intuitively) not actually on the same plane. If you know someone who has trouble seeing distances, you can test this. No matter how close to the mirror.he gets, he'll nevef see something that is a long distance from the mirror to be in focus.



Interesting question though!

Answer 2

Every point on the object can be assumed to be a point-object whose image is formed as far behind the mirror as the object is in front of the mirror.

So if you can imagine, If a perpendicular line is present in the mirror, then all points on that line will have different images but in the same line. Hence you get a straight image.

In case, there is width (3 D), the height factor will also come into consideration.

Actually the image is a collection of various point images which seems to be 3D

Answer 3

The Images of a mirror have a relativity between the actual 3 dimensional event.



The mirror contracts the image of what it actually is in realty. Thus we have an equation of length contraction as if an observer was viewing the event from a long distance. And by the same token observe motion much slower than it acctualy is.



Thus what we see in a mirror is how things appear from a distance.It is a relativity effect.

Answer 4

When the light rays bounce of the mirror, they approach the camera at the same angle as if they'd come from the real object, so don't come together where the screen in your camera is to form a sharp image.

Answer 5

the depth of field you see in the mirror is the distance between the mirror and the camera,so the background was out of focus, because it was the distance from the camera to the background

Answer 6

Wow! What an interesting question! I'm subrcribing to the answers so I find out what people have to say!