The name does not mean that there is only one lens in the optical system, but that the photographer looks through the same lenses that the picture is taken with, instead of looking through a separate ...The name does not mean that there is only one lens in the optical system, but that the photographer looks through the same lenses that the picture is taken with, instead of looking through a separate parallel optical system as in the twin reflex camera. The angular field of view (AFOV) is defined for scenes at large distances and is equal to the angle subtended at the lens by the detector when the image distance is the focal length f, i.e.
