In the field of

photography Photography is the art, application, and practice of creating durable images by recording light, either electronically by means of an image sensor, or chemically by means of a light-sensitive material such as photographic film. It is employed i ...

, a manual focus

camera A camera is an optical instrument that can capture an image. Most cameras can capture 2D images, with some more advanced models being able to capture 3D images. At a basic level, most cameras consist of sealed boxes (the camera body), with a ...

is one in which the user has to adjust the focus of the

lens A lens is a transmissive optical device which focuses or disperses a light beam by means of refraction. A simple lens consists of a single piece of transparent material, while a compound lens consists of several simple lenses (''elements''), ...

by hand. Before the advent of

autofocus An autofocus (or AF) optical system uses a sensor, a control system and a motor to focus on an automatically or manually selected point or area. An electronic rangefinder has a display instead of the motor; the adjustment of the optical system ...

, all cameras had manually adjusted focusing; thus, the term is a retronym. The focus itself may be adjusted in a variety of ways. Larger

view camera A view camera is a large-format camera in which the lens forms an inverted image on a ground-glass screen directly at the film plane. The image is viewed and then the glass screen is replaced with the film, and thus the film is exposed to exact ...

s and the like slide the lens closer or further from the film plane on rails; on smaller cameras, a focus ring on the lens is often rotated to move the lens elements by means of a helical screw. Other systems include levers on the lens or on the camera body. There are a number of ways in which focus may be determined. Simplest is using a distance scale and measuring or estimating distance to the subject. Other methods include the rangefinder, which uses triangulation to determine the distance. On other cameras, the photographer examines the focus directly by means of a focusing screen. On the view camera, this ground glass is placed where the film will ultimately go, and is replaced by a sheet of film once focus is correct. Twin lens reflex cameras use two lenses that are mechanically linked, one for focusing and the other to take the photograph. Single lens reflex cameras, meanwhile, use the same objective lens for both purposes, with a mirror to direct the light to either the focusing screen or the film. Focusing screens, in their simplest form, consist of a matte glass or plastic surface on which the image can be focused. Other devices, such as split-image prisms or microprisms, can help determine focus. Manual focus lenses can also be used on modern digital cameras with an adapter. Zeiss, Leica and Cosina Voigtländer are among current manufacturers who continue to make manual lenses in lens mounts native to modern cameras.

References

{{Reflist Photographic techniques