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Optics technical overview

Focal length, Field of view, Depth of field, Working distance

The focal length and aperture of a lens are usually included in the product name of a lens. However, there are further specifications that are important when selecting the correct optical solution.

Focal length

The focal length of a lens is the distance between its effective centre and the point at which light from infinity will be focused to a single point. The sensor of the camera needs to be positioned behind this point on what is called the image plane.

Field of view or magnification

The magnification ß' of a lens describes the ratio between image size and object size and has a direct connection to the focal length f' of the lens and the working distance a. The following diagram shows how to calculate the ratio between object size, working distance and focal length of the lens.