Single-lens Reflex Camera
A single-lens reflex (SLR) camera is a camera that typically uses a mirror and prism system (hence "reflex", from the mirror's reflection) that permits the photographer to view through the lens and see exactly what will be captured, contrary to viewfinder cameras where the image could be significantly different from what will be captured.
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 above (TLR or twin-lens reflex) or to the side (rangefinder). Because the viewfinder and the film lens cannot share the same optical path, the viewing lens is aimed to intersect with the film lens at a fixed point somewhere in front of the camera. This is not problematic for pictures taken at a middle or longer distance, but parallax causes framing errors in close-up shots. Moreover, focusing the lens of a fast reflex camera when it is opened to wider apertures (such as in low light or while using low-speed film) is not easy.
Most SLR cameras permit upright and laterally correct viewing through use of a roof pentaprism situated in the optical path between the reflex mirror and viewfinder. Light, which comes both horizontally and vertically inverted after passing through the lens, is reflected upwards by the reflex mirror, into the pentaprism where it is reflected several times to correct the inversions caused by the lens, and align the image 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 Canon Pellix film camera was an exception to the moving mirror system, wherein the mirror was a fixed beamsplitting pellicle.
Focus can be adjusted manually by the photographer or automatically by an autofocus system. The viewfinder can include a matte focusing screen located just above the mirror system to diffuse the light. This 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 what the CCD is capturing. However, SLR is still popular in high-end and professional cameras because they are system cameras with interchangeable parts, allowing customization. They also have far less shutter lag, allowing photographs to be timed more precisely. Also the pixel resolution, contrast ratio, refresh rate, and color gamut of an LCD preview screen cannot compete with the clarity and shadow detail of a direct-viewed optical SLR viewfinder.
Read more about Single-lens Reflex Camera: Optical Components, Further Developments, History, Film Formats, Common Features, Advantages, Disadvantages, Future of SLRs
Famous quotes containing the words reflex and/or camera:
“As a medium of exchange,... worrying regulates intimacy, and it is often an appropriate response to ordinary demands that begin to feel excessive. But from a modernized Freudian view, worrying—as a reflex response to demand—never puts the self or the objects of its interest into question, and that is precisely its function in psychic life. It domesticates self-doubt.”
—Adam Phillips, British child psychoanalyst. “Worrying and Its Discontents,” in On Kissing, Tickling, and Being Bored, p. 58, Harvard University Press (1993)
“If I were just curious, it would be very hard to say to someone, “I want to come to your house and have you talk to me and tell me the story of your life.” I mean people are going to say, “You’re crazy.” Plus they’re going to keep mighty guarded. But the camera is a kind of license. A lot of people, they want to be paid that much attention and that’s a reasonable kind of attention to be paid.”
—Diane Arbus (1923–1971)