Accommodation in Eye and Camera

Accommodation is the process of adjusting the focus distance of an optical instrument to the object which is to be viewed. This process is done very differently by the eye and a camera. Accommodation from distant to close objects for the eye is done by rounding out the lens to shorten its focal length, since the image distance to the retina is essentially fixed. Accommodation from distant to close objects for the camera is done by moving the lens further from the film since the focal length is fixed.

The Camera and the Eye

Images are formed in a camera by refraction in a manner similar to image formation in the eye. However, accommodation to image closer objects is done differently in the eye and camera.

True Zoom Telephoto Lens

In a true zoom lens, two or more of the lens elements are moved within a fixed tube to change the focal length while keeping the image in focus on the film. One scheme with the triplet arrangement shown below is to keep the front and back elements at a fixed separation and move them and the center element to accomplish the zoom.

Example

Single-Lens Reflex Camera

The single-lens reflex 35 mm camera is the choice of many serious amateur as well as professional photographers because the light from the object reflects from a mirror and is taken through the eyepiece to the eye of the photographer, in contrast to a viewfinder camera where the photographer is looking through a separate lens at the subject. The advantage of the SLR is that the eye sees approximately what the film will record, so that you can freely interchange lenses, use close-up lenses, etc. and still see what you will

Light is bounced from a mirror through a pentaprism to the viewer's eye while choosing the object for photography. The shutter button lifts the viewing mirror while opening the shutter to allow the light to fall on the film.