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【Concept】
 
     Dual camera, dual-lens reflex camera means. Called the twin-lens reflex viewfinder lens reflex viewfinder type camera.
     Single, double, refers to the camera, that is a single-lens reflex, or twin-lens reflex.
     Now we are more familiar with the SLR, SLR is a camera, two lenses is dual.
     English abbreviation TLR
 
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【History term】
 
     Dual camera originated 130 years ago, and its development process can be divided into two periods, one before World War II, the second is the post-war.
     German dual camera, including RolleiFlex, Rolleicord and Ikoflex belong to the former
     Japanese dual camera, dual like Ricoh, Mamiya C330, belongs to the latter.

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1. It is said that the original shape of the double-reverse camera is bunk house style camera. The camera is called the "Reporter", for the time being it translated as "reporter."
     It was in 1872 in London, England produced, dating back over 137 years.
     For such an old camera, then we may not be able to imagine how much time it takes to do it now seems very simple operations, such as in the focusing screen up to adjust the position of the subject, focus or just replace the cassette, release the shutter, etc. and so on.
     Of course, that time in order to take moving objects, it is more difficult. Although the "reporter" was not yet using the camera mirror device, but its overall look away from our common dual camera later style is not far off.
 
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2. Probably in 1880, some of London's weather observer in order to shoot the clouds of heaven, they think of a way, that is placed in the camera in a mirror reflection to the clouds, so that when people do not have the viewfinder old upturned neck look days, but just look ahead focusing screen on it!

But do not underestimate this improvement, which was the people in the first attempt to set up a camera in the mirror, oh.
     Because it is made for the camera while shooting the clouds, so people call it "the cloud machine", a great technological innovation, so it was born!
     In the cloud machine, two shots from the middle of the gear unit linked together, allowing movement of the lens to achieve synchronization. Moreover, the image on the focusing screen because of the mirror and become erect, you know, before the mirror in there, the image is inverted.
     Cloud machine, is considered a prototype dual camera directly, of course, there are some problems cloud machine is, for example, the body is too great, very practical, and there are serious parallax, not close-range photography, and so on. However, in any case, the significance of the cloud machine in the history of the camera will not be obliterated, because it opens a new chapter in the development of the camera!
 
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【Principle term】
 
     As the name suggests, the biggest feature is the TLR system has two lenses, one directly above one another in.
     The following lenses that transmit images to the film, but the image just above the lens is transmitted for framing and focusing.

People can see the image through the lens above, but in fact only the following lenses really shooting for.
 
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【Digital and film double reverse dual terminology】
 
     The dual-lens digital camera with a dual-lens film before different purposes.
 
1. Kodak's dual-lens viewfinder and imaging capabilities are both, in fact, is the integration of the two single-lens.
     Among them, one is used as a fixed focal length (23 mm) wide-angle lens, the other is used as a variable focal length 3x telephoto lens (39-117 mm), together with a wide-angle focal length, with a total of nearly 5 optical zoom focal length changes .
     When using a wide angle shot, automatic start in the upper part of the lens; when using the telephoto shooting, the lens automatically converted below.
     Moreover, each corresponding to a CCD camera imaging system. Such dual-lens design, to avoid making the problem of power-retractable zoom lens too long.
     Thus, dual camera lens function is not the same.
     As such dual-lens design is a trend, a rare clear.
     According to this design ideas of view, but added a bunch of shots possible integrated multi-lens camera, the need which automatically starts the lens focal length. Like panpipes each tube can sound like a blow.

2. Previously, Rollei also had one pair of vintage camera lens, just one shot is just a decorative role, in fact, a single-lens camera, just to sell the concept of a retro look it, the camera image is poor.

3. The dual-lens camera has been around nearly a hundred years time, however recently, some foreign websites showed a concept digital camera --Clam.
     The two camera lenses are designed for the camera in front and rear ends. With traditional digital cameras is different, Clam using clam-like body shape can be opened and closed, the two lenses were designed in the lens front and rear, a bit like dual camera 3G handsets.
     This feature of the camera is that when you close the camera can shoot scenes on the back of the camera and the photographer in front of the camera, and shoot at the same time to get the self-timer.
     It also supports two composite pictures, create images with artistic effects. When you open the Clam camera that can shoot full-size images and automatically merge, described as a machine can.
     In addition to the two lenses, Clam camera also has two liquid crystal screen, can show different angles captured photos.
 
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【Advantages Terminology】
 
1. Traditional dual lens camera, is used for filming, one for imaging. But generally can not replace the lens, two lenses together, if not replace, then viewing and imaging lens parallax would be great.

2. There is a dual-lens camera imaging feature is the viewfinder lens is often seen in the image on the film with an imaging lens recorded different, there is a disparity.

3. When the viewfinder is too much trouble, it is difficult in focus, have started a magnifying glass to see the viewfinder. If you use it well, and almost SLR camera imaging.

4. Because dual camera viewfinder when the photographer looking down, so when the portrait photography can alleviate the subject's unnatural performance.

5. SLR cameras (SLR) In contrast, dual camera (TLR) camera for more than a viewfinder, mirror is fixed, and thus do not affect the photo exposure during shooting (SLR cameras due to lift and mirror cover the viewfinder screen, invisible image exposure period). Exactly the same on the frosted glass of imaging and film imaging size.
 
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【Term Disadvantages】
 
 1. Since the viewfinder lens and photographic lenses are separated, and the next shaft framing cameras, TLR parallax problem (ie not WYSIWYG).
     When shooting close objects evils of this problem will become more apparent.
     So some modern TLR camera viewfinder built into the system automatically parallax compensation device.

2. Compared with the optical viewfinder or rangefinder, frosted glass on the image is not very bright.

3. You must watch the way down to waist level in front of the object will make the operation very convenient.
     Modern TLR camera adds a called Polo (Porro) eye-level viewfinder viewfinder accessory, can overcome this shortcoming.

4. The twin-lens system on its inherent characteristics, the larger, and when changing lenses, you need to replace two lenses simultaneously;
     This is great for today's fast aperture lenses, it is indeed a problem.

5. lens interchangeability limited. If you replace the camera lens, you must also replace the viewfinder lens.
     Today's TLR cameras typically offer interchangeable twin-lens system.
 
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【Article is excerpted from: Web Search】
【Reserved Integrate / Just Reference】
【Translation is by The Network】