Why is near clip plane necessary?

OK totally noob question here. I have searched but i cculdn’t find a suitable answer. I can understand why the far clip plane is necessary to limit the amount of information drawn on the screen. But why the near clip plane? Why not just start the camera’s view from the camera? If you have a movie camera in real life it records the images in front of it, right, not starting at 4 metres in front of it. So what’s the deal with this one? Be grateful for an explanation.

Here is a great thread regarding the question

http://www.facepunch.com/threads/1075270-What-s-the-point-of-the-near-clipping-plane-in-3d-games

Also you might take a look at the camera matrix(wikipedia).

Actually it’s the other way round. You don’t need a far clipping plane but always a near clipping plane. It’s a perspective projection with the vanishing point is your camera position. When the near-clipping plane distance would be set to 0 your whole scene would be projected onto a single point.

The mathematical background is that when setting up the projection matrix you have to calculate this:

-(2 * zFar * zNear) / (zFar - zNear)

When zNear is 0 all z values would map to 0.

Here’s a nice article about the projection matrix and some tricks how to setup one without far clipping plane.