Why is the image in games on the sides of the screen stretched?

Question

Windows

Hello world,
And I increasingly notice that I seem to have changed something. More precisely, I began to pay attention to the graphics in games, when you turn the camera, objects from the side seem to be stretched. It seems that the projection matrix is ​​responsible for this, but I can’t understand how such a defect occurs.

Answer 1

This also happens in the image that the video camera receives in the real world with a fairly wide viewing angle. Such is the nature of the projection onto the two-dimensional plane of the screen.
Here, I depicted approximately what is happening. An object, when turning the camera or moving the camera forward, for example, increases its projection on the camera matrix, because the matrix is ​​not round, but flat. Therefore, it visually stretches.