Manual focus
Encyclopedia
In the field of photography
, a manual focus camera
is one in which the operator has to adjust the focus
of the lens
by hand. Before the advent of autofocus
, 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
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.
Photography
Photography is the art, science and practice of creating durable images by recording light or other electromagnetic radiation, either electronically by means of an image sensor or chemically by means of a light-sensitive material such as photographic film...
, a manual focus camera
Camera
A camera is a device that records and stores images. These images may be still photographs or moving images such as videos or movies. The term camera comes from the camera obscura , an early mechanism for projecting images...
is one in which the operator has to adjust the focus
Focal length
The focal length of an optical system is a measure of how strongly the system converges or diverges light. For an optical system in air, it is the distance over which initially collimated rays are brought to a focus...
of the lens
Photographic lens
A camera lens is an optical lens or assembly of lenses used in conjunction with a camera body and mechanism to make images of objects either on photographic film or on other media capable of storing an image chemically or electronically.While in principle a simple convex lens will suffice, in...
by hand. Before the advent of autofocus
Autofocus
An autofocus optical system uses a sensor, a control system and a motor to focus fully automatic or on a manually selected point or area. An electronic rangefinder has a display instead of the motor; the adjustment of the optical system has to be done manually until indication...
, all cameras had manually adjusted focusing; thus, the term is a retronym
Retronym
A retronym is a type of neologism that provides a new name for an object or concept to differentiate the original form or version of it from a more recent form or version. The original name is most often augmented with an adjective to account for later developments of the object or concept itself...
.
The focus itself may be adjusted in a variety of ways. Larger view camera
View camera
The view camera is a type of camera first developed in the era of the Daguerreotype and still in use today, though with many refinements. It comprises a flexible bellows which forms a light-tight seal between two adjustable standards, one of which holds a lens, and the other a viewfinder or a...
s and the like slide the lens closer or further from the film plane
Film plane
A film plane is the area inside any image taking device with a lens and a digital sensor or film; such as a camera. The film plane varies in distance from the lens focal point in each manufacturer...
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
Rangefinder
A rangefinder is a device that measures distance from the observer to a target, for the purposes of surveying, determining focus in photography, or accurately aiming a weapon. Some devices use active methods to measure ; others measure distance using trigonometry...
, which uses triangulation to determine the distance. On other cameras, the photographer examines the focus directly by means of a focusing screen
Focusing screen
A focusing screen is a flat translucent material, usually ground glass, found in a system camera that allows the user of the camera to preview the framed image in a viewfinder. Often, focusing screens are available in variants with different etched markings for various purposes...
. 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.