TLR

Twin-lens reflex camera

From Wikipedia, the free encyclopedia

The front of a Kinaflex twin-lens reflex camera. The two lenses are coupled with gears around their circumference in this simple design.

Sketch of an early-20th-century twin-lens reflex camera

A great TLR — the Rolleiflex

Mamiya C220 & Mamiya C330 with typical rollfilm box

1957 Kodak Duaflex IV, an inexpensive fixed-focus TLR

A twin-lens reflex camera (TLR) is a type of camera with two objective lenses of the same focal length. One of the lenses is the photographic objective (the lens that takes the picture), while the other is used for the waist-level viewfinder system. In addition to the objective, the viewfinder consists of a 45-degree mirror (the reason for the word reflex in the name), a matte focusing screen at the top of the camera, and a pop-up hood surrounding it. The two objectives are connected, so that the focus shown on the focusing screen will be exactly the same as on the film. However, many inexpensive TLRs are fixed-focus models. Most TLRs use leaf shutters with shutter speeds up to 1/500th sec with a B setting.

Higher-end TLRs may have a pop-up magnifying glass to assist the user in focusing the camera. In addition, many have a "sports finder" consisting of a square hole punched in the back of the pop-up hood, and a knock-out in the front. Photographers can sight through these instead of using the matte screen. This is especially useful in tracking moving subjects such as animals or race cars, since the image on the matte screen is reversed left-to-right. It is nearly impossible to judge composition with such an arrangement, however.

Mamiya's C-Series, introduced in the 1960s, the C-3, C-2, C-33, C-22 and the Mamiya C330 and Mamiya C220 along with their predecessor the Mamiyaflex,^[1] are the only conventional TLR cameras to feature truly interchangeable lenses.^[2] The Mamiya SLRs also employ bellows focusing, making extreme closeups possible.

Rollei Rolleiflex model TLRs have an additional feature for the "sports finder" that allows precise focusing. When the hinged front hood knock-out is moved to the sports finder position a secondary mirror swings down over the view screen to reflect the image to a secondary magnifier on the back of the hood, just below the direct view cutout. This permits precise focusing while using the sports finder feature. The magnified central image is reversed both top-to-bottom and left-to-right.

TLRs are different from single-lens reflex cameras (SLR) in several respects. First, unlike virtually all SLRs, TLRs provide a continuous image on the finder screen. The view does not black out during exposure. Additionally, models with leaf shutters rather than focal-plane shutters can synchronize with flash at higher speeds than can SLRs. However, because the photographer views through one lens but takes the photograph through another, parallax error makes the photograph different from the view on the screen. This difference is negligible when the subject is far away, but is critical for nearby subjects. For accuracy in tabletop photography, in which the subject might be within a foot (30 cm) of the camera, devices are available that move the camera upwards so that the taking lens goes to the exact position that the viewing lens occupied. This solves the parallax problem but it is still impossible to preview depth of field as one can with an SLR, as the TLR's viewing lens has no diaphragm.

A primary advantage of the TLR is its simplicity as compared to the more common single-lens reflex cameras. The SLR must employ some method of blocking light from reaching the film during focusing, either with a focal plane shutter (most common) or with the reflex mirror itself. Both methods add significant noise to the camera's operation. Most TLRs use a leaf shutter in the lens. The only mechanical noise during exposure is from the shutter leaves opening and closing. Most TLRs are also significantly lighter in weight than a medium format SLR.

Another advantage of the TLR design can be seen when long exposures are required. During exposure, an SLR's mirror must be retracted, blacking out the image in the viewfinder. A TLR's mirror is fixed and the taking lens remains open throughout the exposure, letting the photographer examine the image while the exposure is in progress. This can ease the creation of special lighting or transparency effects.

The TLR is especially useful for action portrait photography (e.g., martial arts portraits) as the action of the shutter can be very responsive to the photographer compared to the time required to move the mirror of an SLR. Owing to the availability of medium-format cameras and the ease of image composition, it is also preferred by many portrait studios for static poses.

The typical TLR is medium format, using 120 roll film with square 6×6 cm images. Presently, the Chinese Seagull Camera and the German Rollei are in production, but in the past, many manufacturers made them. Models with the Mamiya, Minolta and Yashica brands are common on the used-camera market, and many other companies made TLRs that are now classics. The Mamiya C series TLRs had interchangeable lenses, allowing focal lengths from 55mm (wide angle) to 250mm (telephoto) to be used. The simple, sturdy construction of many TLRs means many have endured the years well. Many low-end cameras used cheap shutters however, and the slow speeds on these often stick or are inaccurate.

There were smaller TLR models, using 127 roll film with square 4×4 cm images, most famous the "Baby" Rolleiflex and the Yashica 44. The TLR design was also popular in the 1950s for inexpensive fixed focus cameras such as the Kodak Duaflex and Argus 75. Though most used medium format film, a few 35mm TLRs were made, the Contaflex TLR being the most elaborate, with interchangeable lenses and removable backs.

The smallest TLR camera is the Swiss-made Tessina, using perforated 35mm film forming images of 14×21 mm.

SLR

Single-lens reflex camera

From Wikipedia, the free encyclopedia

The historic Contax S, 1949, the first pentaprism SLR for eye-level viewing

The single-lens reflex (SLR) camera uses an automatic moving mirror system which permits the photographer to see exactly what will be captured by the film or digital imaging system, as opposed to non-SLR cameras where the view through the viewfinder could be significantly different from what was captured on film.

Prior to the development of SLR, all cameras with viewfinders had two optical light paths: one path through the lens to the film, and another path positioned slightly off to the side seen by the photographer. Because the viewfinder and the film lens cannot share the same optical path, the viewfinder is aimed to intersect with the film lens at a fixed point somewhere in front of the camera. This is more or less helpful for pictures taken at a middle or longer distance but a close-up shot framed in the viewfinder will not look the same as the film image. Moreover, focusing the lens of a non-SLR camera when it is opened to wider apertures (such as in low light or while using low-speed film) is not easy.

SLR cameras permit direct viewing using a pentaprism situated above the optical path through the lens to the film plane. Light is reflected by a movable mirror upwards into the pentaprism where it is reflected several times until it aligns with the viewfinder. When the shutter is released, the mirror moves out of the light path and the light shines directly onto the film, or in the case of a DSLR, the CCD or CMOS imaging sensor.

The focus can be adjusted manually by the photographer or automatically by the autofocus system. The viewfinder can include a matte focusing screen located just above the mirror system to diffuse the light. This system permits accurate viewing, composing and focusing, especially useful with interchangeable lenses.

Up until the 1990s, SLR was the most advanced photographic preview system available. But the recent development and refinement of digital imaging technology with an on-camera live LCD preview screen has overshadowed SLR's popularity. Nearly all inexpensive compact digital cameras now include an LCD preview screen allowing the photographer to see exactly what the CCD is capturing. However, SLR is still popular in high-end and professional cameras, because the pixel resolution, contrast ratio, and color gamut of an LCD preview screen cannot compete with the clarity and shadow detail of a direct-viewed optical SLR viewfinder.

Common camera types

This is the types of camera. I'll explain each type later.

SLR
TLR
Point-And-Shoot
Rangefinder
Viewfinder
Box
Folding
Subminiature
View Camera
Pinhole Camera

Camera Types - Distinguishing features

There are many types of cameras. Almost all of them can be classified according to the following features:

• the sensor: nature (digital, 35mm film, 120 film, APS film, other rollfilm, cut film...) and size (24×36mm, 6×6cm...);
• the viewing system (external finder, electronic finder, LCD screen, single lens reflex, twin lens reflex...);
• the rigidity of the body (rigid, swivelling lens, telescopic tube, folding, monorail...);
• the focusing system (autofocus, rangefinder focusing, manual reflex focusing, guess focusing, ground glass back...);
• the lens attachment (interchangeable lens, non interchangeable zoom lens, fixed lens);
• the metering system: metering sensor and metering modes (programmed, speed-priority, aperture-priority, manual).

The features that will most determine the aspect of the camera are the viewing system and the rigidity. Once they are known, the general shape of the body is usually quite predictable.

The size of the sensor matters for the size of the camera and for the end result, while its nature has an incidence on the internal construction: a film camera usually needs place for the supply and take up spools, except for the cameras using cut film or plate film.

The focusing system and metering system will mostly influence how you will use the camera, but has few impact on its shape.

Unusual combinations of these features have existed, for example folding TLRs, subminiature SLRs and so on. However not every combination does make sense. For example an subminiature folding autofocus TLR is not theoretically impossible, but unlikely to ever exist.

(taken from http://www.camerapedia.org/wiki/Camera_Types)

How Cameras Work

by Tom Harris

A fully manual single-lens-reflex camera.

­ Photography is undoubtedly one of the most important inventions in history -- it has truly transformed how people conceive of the world. Now we can "see" all sorts of things that are actually many miles -- and years -- away from us. Photography lets us capture moments in time and preserve them for years to come.

The basic technology that makes all of this possible is fairly simple. A still film camera is made of three basic elements: an optical element (the lens), a chemical element (the film) and a mechanical element (the camera body itself). As we'll see, the only trick to photography is calibrating and combining these elements in such a way that they record a crisp, recognizable image.

There are many different ways of bringing everything together. In this article, we'll look at a manual single-lens-reflex (SLR) camera. This is a camera where the photographer sees exactly the same image that is exposed to the film and can adjust everything by turning dials and clicking buttons. Since it doesn't need any electricity to take a picture, a manual SLR camera provides an excellent illustration of the fundamental processes of photography.

The optical component of the camera is the lens. At its simplest, a lens is just a curved piece of glass or plastic. Its job is to take the beams of light bouncing off of an object and redirect them so they come together to form a real image -- an image that looks just like the scene in front of the lens.

But how can a piece of glass do this? The process is actually very simple. As light travels from one medium to another, it changes speed. Light travels more quickly through air than it does through glass, so a lens slows it down.

When light waves enter a piece of glass at an angle, one part of the wave will reach the glass before another and so will start slowing down first. This is something like pushing a shopping cart from pavement to grass, at an angle. The right wheel hits the grass first and so slows down while the left wheel is still on the pavement. Because the left wheel is briefly moving more quickly than the right wheel, the shopping cart turns to the right as it moves onto the grass.

The effect on light is the same -- as it enters the glass at an angle, it bends in one direction. It bends again when it exits the glass because parts of the light wave enter the air and speed up before other parts of the wave. In a standard converging, or convex lens, one or both sides of the glass curves out. This means rays of light passing through will bend toward the center of the lens on entry. In a double convex lens, such as a magnifying glass, the light will bend when it exits as well as when it enters.

This effectively reverses the path of light from an object. A light source -- say a candle -- emits light in all directions. The rays of light all start at the same point -- the candle's flame -- and then are constantly diverging. A converging lens takes those rays and redirects them so they are all converging back to one point. At the point where the rays converge, you get a real image of the candle. In the next couple of sections, we'll look at some of the variables that determine how this real image is formed.

History of Camera

From Wikipedia, the free encyclopedia

Camera obscura.

The forerunner to the camera was the camera obscura. The camera obscura is an instrument consisting of a darkened chamber or box, into which light is admitted through a convex lens, forming an image of external objects on a surface of paper or glass, etc., placed at the focus of the lens. The camera obscura was first invented by the Iraqi scientist Ibn al-Haytham (Alhazen) as described in his Book of Optics (1015-1021). Irish scientist Robert Boyle and his assistant Robert Hooke later developed a portable camera obscura in the 1660s.

The first camera that was small and portable enough to be practical for photography was built by Johann Zahn in 1685, though it would be almost 150 years before technology caught up to the point where this was practical. Early photographic cameras were essentially similar to Zahn's model, though usually with the addition of sliding boxes for focusing. Before each exposure, a sensitized plate would be inserted in front of the viewing screen to record the image. Jacques Daguerre's popular daguerreotype process utilized copper plates, while the calotype process invented by William Fox Talbot recorded images on paper.

The first permanent colour photograph, taken by James Clerk Maxwell in 1861.

The first permanent photograph was made in 1826 by Joseph Nicéphore Niépce using a sliding wooden box camera made by Charles and Vincent Chevalier in Paris. Niépce built on a discovery by Johann Heinrich Schultz (1724): a silver and chalk mixture darkens under exposure to light. However, while this was the birth of photography, the camera itself can be traced back much further. Before the invention of photography, there was no way to preserve the images produced by these cameras apart from manually tracing them.

The development of the collodion wet plate process by Frederick Scott Archer in 1850 cut exposure times dramatically, but required photographers to prepare and develop their glass plates on the spot, usually in a mobile darkroom. Despite their complexity, the wet-plate ambrotype and tintype processes were in widespread use in the latter half of the 19th century. Wet plate cameras were little different from previous designs, though there were some models, such as the sophisticated Dubroni of 1864, where the sensitizing and developing of the plates could be carried out inside the camera itself rather than in a separate darkroom. Other cameras were fitted with multiple lenses for making cartes de visite. It was during the wet plate era that the use of bellows for focusing became widespread.

The first colour photograph was made by Scottish physicist James Clerk Maxwell, with the help of English inventor and photographer Thomas Sutton, in 1861

What is Camera?

Camera

From Wikipedia, the free encyclopedia

A modern single-lens reflex camera

Left to right: an Agfa box camera, a Polaroid Land camera, and a Yashica 35 mm SLR

A camera is a device that records images, either as a still photograph or as moving images known as videos or movies. The term comes from the camera obscura (Latin for "dark chamber"), an early mechanism of projecting images where an entire room functioned as a real-time imaging system; the modern camera evolved from the camera obscura.

Cameras may work with the light of the visible spectrum or with other portions of the electromagnetic spectrum. A camera generally consists of an enclosed hollow with an opening (aperture) at one end for light to enter, and a recording or viewing surface for capturing the light at the other end. A majority of cameras have a lens positioned in front of the camera's opening to gather the incoming light and focus all or part of the image on the recording surface. The diameter of the aperture is often controlled by a diaphragm mechanism, but some cameras have a fixed-size aperture.