What is a reflex camera? When I read the characteristics of cameras, It`s common to see this. I think that probably a reflex camera is a camera which you can change the lens, but I'm not sure.

I know, maybe it's a silly question but I don't know.

Thanks for the help in advance.

up vote 7 down vote accepted

A reflex is defined by its mirror. Most reflex cameras have interchangeable lenses but this is not always the case and many interchangeable lens cameras have no mirror and hence are not reflex cameras. This is why modern ILCs are often called mirrorless.

The mirror is used to direct light that comes from the lens to be reflecting into the viewfinder. This lets the photographer frame with great precision. Compare this to a range-finder or camera with an optical tunnel where view is made by a separate optical path and so shows parallax error and may even be partially obstructed by the lens.

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    As an example of reflex cameras without interchangeable lenses, see Olympus' iS/L-Series of autofocus film cameras from the 1990s, which it labelled "Zoom Lens Reflex": olympus-global.com/en/corc/history/camera/l_series – osullic Aug 27 '16 at 16:56
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    There are single lens reflex cameras (SLRs), and there are twin-lens reflex cameras (TLRs). The twin-lens kind have the same parallax issues that a rangefinder camera has. – Solomon Slow Aug 27 '16 at 18:28
  • @james As an incidental aside, I have a distinct memory of going into a camera store about 3 years ago and asking if they stocked any second-hand "twin-lens reflex" cameras. The assistant, a man whose appearance would have made him contemporaneous with the popular days of TLRs, tried to convince me that there was no such thing as a "twin-lens reflex", only a "twin-lens camera". I left without arguing. – osullic Sep 2 '16 at 22:06

A reflex camera is simply one that has a mirror in its guts. It allows the light coming in from a lens to be reflected up into a viewfinder or onto ground glass so the photographer can see the image and adjust composition before taking it.

This is in contrast to, say, a view camera (the kind with bellows), where the light just goes straight through to the image plane/ground glass [so it appears upside down and reversed left-to-right]; a rangefinder, where you view the scene straight through a separate lens next to the one used to take the image; or a digital mirrorless or compact camera, where light goes directly to the sensor and sensor data is conveyed to the viewfinder/LCD.

Most reflex cameras are in one of two categories: SLR or TLR.

  • Single-lens reflex (SLR) cameras are by far the most prevalent and have supplanted the older TLR cameras and these days come with digital sensors. The lens reflected by the mirror up into the viewfinder is then passed through a pentamirror or pentaprism to flip the image around so it appears in the eye-level viewfinder the same way the scene does, rather than upside down and left-to-right reversed.

  • Twin-lens reflex (TLR) cameras use two lenses: one for taking an image, the other for the viewfinder. The viewfinder lens is usually stacked over the taking lens. So you have two separate lightpaths and parallax, like with a rangefinder. But the viewfinder lens's light is projected up onto ground glass, and you compose looking down at the glass at waist level (i.e., a waist-level viewfinder). But, the image on the glass is reversed left-to-right. TLRs never really went digital, and mostly remain a specialist tool for medium-format film enthusiasts.

A reflex camera is a camera with a reflex mirror, the purpose of which is to throw the image coming through the lens into the viewfinder. The reflex part comes from the fact that, when you press the shutter button, the mirror raises up to allow the light to hit the sensing medium (sensor or film).

You have probably read about DSLRs. DSLR stands for Digital Single Lens Reflex, ie it has a digital sensor, it uses the same lens for both the viewfinder and the imaging medium, and has a reflex mirror.

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    "Reflex" only means that there is a mirror in the viewfinder optical path. It doesn't necessarily mean that the mirror moves (e.g., a typical Twin Lens Reflex camera would have a non-moving mirror) en.wikipedia.org/wiki/Twin-lens_reflex_camera – Solomon Slow Aug 27 '16 at 18:30
  • Canon had some fixed mirror SLR cameras back in the film days (probably others, too) and sony did this for digital without an optical viewfinder with the fixed mirror in place only for AF. They call that thing SLT (T for translucent). – null Aug 27 '16 at 22:50
  • The Canon Pellix was introduced in 1965, the Canon F-1 Hi-Speed with pellicle mirror came out just in time for the 1972 Olympics, and the "New F-1" that could do 14 fps was released in 1984. Two EOS models, The RT and the 1N Rs, were pellicle mirror versions of the otherwise identical conventional mirrored models 600/630 and 1N. – Michael C Aug 27 '16 at 23:32

Consider "reflex" as an abbreviation for "reflection". That's it. It implies that a mirror is utilised in the camera to reflect and project the image to your view finder.

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    +1, although it is not so much an abbreviation as just another word for. – mattdm Nov 12 '17 at 5:33

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