Twin-Lens Reflex Camera
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The twin-lens reflex (TLR) camera,
formerly the mainstay of magazine photographers for many years, remains
popular with both professional and amateur photographers. It is most
commonly used in the 21/4 x 21/4 inch format, but can be had in formats
as small as 35 mm or as large as 4 x 5 inches.
Twin-lens reflex cameras can vary in shape and proportions and this
type of camera is basically two box-body cameras placed one atop the
other, with one mechanism controlling the focusing of the two lenses.
The lower lens, the "taking" lens, forms the image directly on the
film, while the upper lens, the "viewing" lens, has its light path
deflected upward to a horizontal ground glass viewing screen. This
screen is usually protected by a collapsible hood to prevent stray
light from obscuring the image.
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Within the hood is a folding magnifier,
which aids in accurate focusing when it is swung into position over the
ground glass. In operation, the photographer holds the camera at waist
or chest level, looks into the top of the camera while framing and
focusing the image, and makes the picture when ready.
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The viewing lens has no shutter, and
usually no iris diaphragm. The shutter mechanism on the taking lens is
of the between-the-lens leaf type, with the diaphragm incorporated in
it. The twin-lens reflex combines certain features of both the
rangefinder and SLR designs. In one sense it is a rangefinder camera
with an exceptionally large viewfinder; in another sense it is a reflex
design, but with the mirror permanently out of the taking lens light
path, so that it requires its own image-forming lens.
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The twin-lens reflex is not an inherently
versatile camera, but it does have certain advantages. It is an
exceptionally easy camera with which to learn basic photography. Most
people find it easy to handle and pleasant to operate. The shutter is
almost noiseless, and the waist-level viewing position makes it quite
inconspicuous to use. (For instance, it is well out of sight from the
side when hanging by its neck strap between the flaps of an open coat
or jacket.) The 21/4 x 21/4 inch negative is larger than 35 mm, an
advantage with respect to image quality. The shutter is readily
synchronized to any type of flash at any speed. The viewfinder is
usually large and brilliant.
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There are several disadvantages. Most
models come with lenses of only one focal length and are without
provisions for interchanging. A very few types offer limited
interchangeability of lenses, with pairs of matching lenses being
mounted on a single interchangeable front plate. Obviously, such
interchangeability is limited to lenses made for the specific camera,
and is expensive because lenses must be in matched pairs. The
alternative, is use two cameras with different lens types, is not
entirely satisfactory, either. It is annoying to have more than one
camera hanging about one's person at any given and doing so requires
care to prevent damage from banging them together. So having two
complete cameras with different lenses is less than satisfactory, as
well as being expensive.
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Depth of field cannot be checked directly
on the ground glass unless a diaphragm is on the viewing lens-and this
is seldom the case. Waist-level viewing results in "seeing the world
through one's navel," often not a suitable angle of view. In addition,
the simple mirror-type viewer of most twin-lens reflex cameras reverses
the image laterally, which, by reversing the apparent direction of
cross-axis movement, makes following fast motion quite difficult. This
angle-of-view problem can be partially corrected by use of a "sports
viewfinder," a simple open frame and peepsight device built into the
viewer hood. A few twin-lens reflex cameras can be equipped with a
prism or other optical system that erects the image to allow eye-level
viewing and corrects the lateral reversal. But the sports viewfinder
makes accurate framing chancy while removing all possibility of judging
the depth of field, and the eye-level prism increases the camera's
weight, bulk, and cost.
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Close-up subjects can be photographed
only when slip-on supplementary lenses are added. These lenses, however
well made, tend to degrade the image, and usually require additional
special devices to aid in accurate composition and focusing. The
viewing and taking lenses being separated in space, the two separate
angles of view produce image displacement or parallax. There is no
difficulty in long-distance viewing, and relatively little at
intermediate distances. But there is too much parallax in the twin lens
viewing system for accurate viewing at really close distances. The more
expensive cameras feature built-in parallax correction; the viewing
lens is canted forward to include the same field of view in the plane
of prime focus as the taking lens. This still does not provide an
identical angle of view, and thus the foreground-background overlaps
will differ in viewing and on the film. Even where correction is
provided, and where it remains satisfactory in use, it is usually
operative only down to about three feet from the lens. At closer
distances the only real way to avoid parallax problems is to make use
of a vertical-shift device on a tripod after composing and focusing, to
place the taking lens in the former position of the viewing lens before
exposing the film.
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The subject area in which the twin-lens
reflex camera is most at home is the photography of people and their
surroundings. As stated earlier, it has done noble service in magazine
illustration, and has also done yeoman service in field ethnology in
the last several decades.
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