Viewfinder - AbsoluteAstronomy.com

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 viewfinder is what the photographer looks through to compose, and in many cases to focus, the picture. Most viewfinders are separate, and suffer parallax

Parallax

Parallax is a displacement or difference in the apparent position of an object viewed along two different lines of sight, and is measured by the angle or semi-angle of inclination between those two lines. The term is derived from the Greek παράλλαξις , meaning "alteration"...

, while the single-lens reflex camera

Single-lens reflex camera

A single-lens reflex camera is a camera that typically uses a semi-automatic moving mirror system that permits the photographer to see exactly what will be captured by the film or digital imaging system, as opposed to pre-SLR cameras where the view through the viewfinder could be significantly...

lets the viewfinder use the main optical system. Viewfinders are used in many 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...

s of different types: still and movie, film, analog and digital. A zoom camera usually zooms its finder in sync with its lens, one exception being 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...

cameras.

History

Before the development of microelectronics

Microelectronics

Microelectronics is a subfield of electronics. As the name suggests, microelectronics relates to the study and manufacture of very small electronic components. Usually, but not always, this means micrometre-scale or smaller,. These devices are made from semiconductors...

and electronic display devices, viewfinders were optical.

Direct optical viewfinders

Direct viewfinders were essentially miniature Galilean telescopes; the viewers eye was placed at the back, and the scene viewed through the viewfinder optics. There was some parallax error as the viewfinder was offset from 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...

axis; the view was seen from a point above and usually to one side of the lens. The error varied at different distances, being negligible for distant scenes, and very large for close-up

Close-up

In filmmaking, television production, still photography and the comic strip medium a close-up tightly frames a person or an object. Close-ups are one of the standard shots used regularly with medium shots and long shots . Close-ups display the most detail, but they do not include the broader scene...

s. Viewfinders often had lines visible to the viewer which indicated the edge of the region which would be included in the photograph. More sophisticated cameras with direct viewfinders had coincidence (split-image) rangefinder

Coincidence rangefinder

A coincidence rangefinder is a type of rangefinder that uses mechanical and optical principles to allow an operator to determine the distance to a visible object....

s, initially with separate windows from the viewfinder, later integrated with it; they were called rangefinder camera

Rangefinder camera

A rangefinder camera is a camera fitted with a rangefinder: a range-finding focusing mechanism allowing the photographer to measure the subject distance and take photographs that are in sharp focus...

s. Cameras with interchangeable lenses had to indicate the field of view of each lens in the viewfinder; more usually, interchangeable viewfinders to match the lenses were used.

Waist-level (reflecting) viewfinders

Simple reflecting viewfinders comprised a small forward-looking lens, a small mirror at 45° behind it, and a lens at the top; the user held the camera at waist level and looked down into the viewfinder, where a small image could be seen. Such viewfinders were integrated into box camera

Box camera

The box camera is, with the exception of the pin hole camera, a camera in its simplest form. The form of the classic box camera is no more than a cardboard or plastic box with a lens in one end and film at the other. A simple box camera has only a single element meniscus fixed focus lens and...

s, and fitted to the side of folding camera

Folding camera

A folding camera is a camera that can be folded to a compact and rugged package when not in use. The camera objective is sometimes attached to a pantograph-like mechanism, in which the lid usually is a component. The objective extends to give correct focus when unfolded. A cloth or leather bellows...

s. These viewfinders were fitted to inexpensive cameras.

Sportsfinder (sports viewfinder)

For many sports and press applications optical viewfinders gave too small an image. and were inconvenient to use for scenes that were changing rapidly. For these purposes a simple arrangement of two wire rectangles, a smaller one nearer the eye and a larger one further away, was used, with no optics; the two rectangles were aligned so the smaller one was centred in the larger, and the larger rectangle would give an indication of what would be included. This was fast and convenient to use, but not particularly accurate; cameras with sportsfinders usually had optical viewfinders too.

Twin-lens reflex viewfinders

Twin-lens reflex (TLR) cameras had a large lens above the taking lens, and a large mirror at 45°, projecting an image onto a ground glass screen viewable from above, with the camera at waist level. The viewfinder lens was of similar size and focal length to the taking lens, though the optical quality was less critical; the mirror was of similar size to the film. These cameras were relatively expensive; the Rolleiflex

Rolleiflex

Rolleiflex is the name of a long-running and diverse line of high-end cameras originally made by the German company Franke & Heidecke, and later Rollei-Werk. The "Rolleiflex" name is most commonly used to refer to Rollei's premier line of medium format twin lens reflex cameras...

and cheaper sister Rolleicord

Rolleicord

The Rolleicord was a popular medium-format twin lens reflex camera made by Franke & Heidecke between 1933 and 1976. It was a simpler, less expensive version of the high-end Rolleiflex TLR, aimed at amateur photographers who wanted a high-quality camera but could not afford the expensive Rolleiflex...

were the pioneers. Both single- and twin-lens reflexes allowed focussing by adjusting the lens until the image was sharp.

Single-lens reflex viewfinders

Single-lens reflex (SLR) cameras viewed the scene through the taking lens. Early SLRs were plate cameras, with a mechanism to insert a mirror between the lens and the film which reflected the light upwards, where it could be seen at waist level on a ground glass screen. When ready to take the picture, the mirror was pivoted out of the way (without moving the camera). Later SLRs had a mechanism which flipped the mirror out of the way when the shutter

Shutter

Shutter may refer to:Windows:*Window shutter, a solid window covering used to block light and winds*Plantation Shutters/Jigsaw Shutters, interior wooden louvred shutters to control heat, light and privacy...

button was pressed, followed immediately by the shutter opening. Instead of a waist-level arrangement, a prism was used to allow the camera to be held to the eye. The big advantage of the SLR was that any lens, or other optical device, could be used; the viewfinder always showed exactly the image that would be projected onto the film. Digital camera viewfinders negate this particular advantage of the SLR, as they also show the image exactly as it will be recorded, with no additional optics or parallax error.

Modern viewfinders

Viewfinders can be optical or electronic. An optical viewfinder is simply a reversed telescope

Telescope

A telescope is an instrument that aids in the observation of remote objects by collecting electromagnetic radiation . The first known practical telescopes were invented in the Netherlands at the beginning of the 1600s , using glass lenses...

mounted to see what the camera will see. Its drawbacks are many, but it also has advantages; it consumes no power, it does not wash out in sunlight, and it has "full resolution" (i.e. the resolution of the photographer's eye). An electronic viewfinder

Electronic viewfinder

An electronic viewfinder or EVF is a viewfinder where the image captured by the lens is projected electronically onto a miniature display. The image on this display is used to assist in aiming the camera at the scene to be photographed.-Operation:...

(EVF) is a CRT

Cathode ray tube

The cathode ray tube is a vacuum tube containing an electron gun and a fluorescent screen used to view images. It has a means to accelerate and deflect the electron beam onto the fluorescent screen to create the images. The image may represent electrical waveforms , pictures , radar targets and...

, LCD

Liquid crystal display

A liquid crystal display is a flat panel display, electronic visual display, or video display that uses the light modulating properties of liquid crystals . LCs do not emit light directly....

or OLED

Organic light-emitting diode

An OLED is a light-emitting diode in which the emissive electroluminescent layer is a film of organic compounds which emit light in response to an electric current. This layer of organic semiconductor material is situated between two electrodes...

based display device, though only the LCD is commonplace today due to size and weight. In addition to its primary purpose, an electronic viewfinder can be used to replay previously captured material, and as an on-screen display

On-screen display

An on-screen display is an image superimposed on a screen picture, commonly used by modern television sets, VCRs, and DVD players to display information such as volume, channel, and time.-History:...

to browse through menus.

A still camera's optical viewfinder typically has one or more small supplementary LED

Light-emitting diode

A light-emitting diode is a semiconductor light source. LEDs are used as indicator lamps in many devices and are increasingly used for other lighting...

displays surrounding the view of the scene. On a film camera, these displays show shooting information such as the shutter speed

Shutter speed

In photography, shutter speed is a common term used to discuss exposure time, the effective length of time a camera's shutter is open....

and aperture

Aperture

In optics, an aperture is a hole or an opening through which light travels. More specifically, the aperture of an optical system is the opening that determines the cone angle of a bundle of rays that come to a focus in the image plane. The aperture determines how collimated the admitted rays are,...

and, for 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...

cameras, provide an indication that the image is correctly focussed. Digital still cameras will typically also display information such as the current ISO

Film speed

Film speed is the measure of a photographic film's sensitivity to light, determined by sensitometry and measured on various numerical scales, the most recent being the ISO system....

setting and the number of remaining shots which can be taken in a burst. Another display which overlays the view of the scene is often provided. It typically shows the location and state of the camera's provided auto-focus points. This overlay can also provide lines or a grid which assist in picture composition.

It is not uncommon for a camera to have two viewfinders. For example, a digital still camera may have an optical viewfinder and an electronic one. The latter can be used to replay previously captured material, has an on-screen display

On-screen display

An on-screen display is an image superimposed on a screen picture, commonly used by modern television sets, VCRs, and DVD players to display information such as volume, channel, and time.-History:...

, and can be switched off to save power. A camcorder

Camcorder

A camcorder is an electronic device that combines a video camera and a video recorder into one unit. Equipment manufacturers do not seem to have strict guidelines for the term usage...

may have two viewfinders, both electronic. The first is viewed through a magnifying eyepiece, and due to a rubber eyepiece it can be viewed perfectly even in bright light. The second viewfinder would be larger, of a higher resolution, and may be mounted on the side of the camera. Because it consumes more power, a method is often provided to turn it off to save energy.

Some special purpose cameras do not have viewfinders at all. These are, for example, web camera

Webcam

A webcam is a video camera that feeds its images in real time to a computer or computer network, often via USB, ethernet, or Wi-Fi.Their most popular use is the establishment of video links, permitting computers to act as videophones or videoconference stations. This common use as a video camera...

s and video surveillance

Closed-circuit television

Closed-circuit television is the use of video cameras to transmit a signal to a specific place, on a limited set of monitors....

cameras. They use external monitor

Computer display

A monitor or display is an electronic visual display for computers. The monitor comprises the display device, circuitry, and an enclosure...

s as their viewfinders.