Center ray

In geometric optics , the center beam is a construction aid for the beam path in an optical system.

For this purpose, it is drawn from the object point to be imaged to the point of intersection of the optical axis with the main plane on the object side , further along the axis to the point of intersection with the main plane on the image side and from there parallel to the (imaginary) extension of the first section.

In thin, symmetrical lenses, the main planes coincide with the plane of symmetry of the lens and the point of intersection between the main planes and the optical axis lies in the geometric center of the lens. The route along the axis is therefore omitted in the construction.

The central ray intersects with the parallel ray and the focal ray ; the position of the image point can be determined by constructing this intersection.