<Table> <Tr> <Td> </Td> </Tr> <Tr> <Td> With a simple lens, much more light can be brought into sharp focus . </Td> </Tr> </Table> <Tr> <Td> With a simple lens, much more light can be brought into sharp focus . </Td> </Tr> <P> From the front of the camera, the small hole (the aperture), would be seen . The virtual image of the aperture as seen from the world is known as the lens's entrance pupil; ideally, all rays of light leaving a point on the object that enter the entrance pupil will be focused to the same point on the image sensor / film (provided the object point is in the field of view). If one were inside the camera, one would see the lens acting as a projector . The virtual image of the aperture from inside the camera is the lens's exit pupil . In this simple case, the aperture, entrance pupil, and exit pupil are all in the same place because the only optical element is in the plane of the aperture, but in general these three will be in different places . Practical photographic lenses include more lens elements . The additional elements allow lens designers to reduce various aberrations, but the principle of operation remains the same: pencils of rays are collected at the entrance pupil and focused down from the exit pupil onto the image plane . </P> <P> A camera lens may be made from a number of elements: from one, as in the Box Brownie's meniscus lens, to over 20 in the more complex zooms . These elements may themselves comprise a group of lenses cemented together . </P>

Camera uses which lens to form an image