Camera

A camera combines an image-forming arrangement with a surface that records the incident light. An optical lens collects many light rays from each object point and directs them toward a corresponding image point; a photographic emulsion or photodetector then records the image. The optical camera is the imaging part of this arrangement.

The simplest demonstration replaces the optical lens with an optical pinhole. In NASA's two-card activity, foil containing a small hole covers a window in one card, and a second white card receives the projected image of the Sun. Increasing the separation enlarges the image; making several holes produces several images. The receiving card is viewed from the side, rather than looking through the hole at the Sun.^[ref]

An optical pinhole selects narrow bundles of light rays without refraction. A finite hole also produces geometric blur, and an extremely small hole makes diffraction important. These competing effects explain why reducing the hole indefinitely does not produce unlimited spatial resolution.

The camera center is the center of projection in an ideal perspective camera model: the common origin of its viewing rays. It is a point in scene space, distinct from a principal point, which is an image-plane coordinate. Two distinct camera centers define the camera baseline used by stereoscopy.

For the calibrated perspective projection model $q\sim K(RP+t)$, where $R$ is a rotation matrix, the camera center $C$ satisfies $RC+t=0$. HenceThis follows by applying the inverse rotation to the zero camera-space position.^[ref] For $R=I$ and $t=(-0.1,0,0)$ metres, $C=(0.1,0,0)$ metres: the translation parameter is not directly the world-space camera center. Rotating about that center changes viewing directions without creating a new triangulation baseline.