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A teleside converter (also known as a telephoto conversion lens or a front mount teleconverter) is a
secondary lens In photography, a secondary lens or accessory lens is a lens designed to be used in conjunction with another lens, called the ''primary lens''. A secondary lens may be designed to be used either in front of the primary lens, between it and the ...
which is mounted on the front of a
photographic lens A camera lens (also known as photographic lens or photographic objective) is an optical lens or assembly of lenses used in conjunction with a camera body and mechanism to make images of objects either on photographic film or on other media capab ...
to increase the
effective focal length The focal length of an optical system is a measure of how strongly the system converges or diverges light; it is the inverse of the system's optical power. A positive focal length indicates that a system converges light, while a negative focal ...
of the lens they are attached to. They are used on cameras and video cameras with non–interchangeable lenses to increase the
magnification Magnification is the process of enlarging the apparent size, not physical size, of something. This enlargement is quantified by a calculated number also called "magnification". When this number is less than one, it refers to a reduction in si ...
of the image. Their design is usually that of an afocal
Galilean telescope A refracting telescope (also called a refractor) is a type of optical telescope that uses a lens as its objective to form an image (also referred to a dioptric telescope). The refracting telescope design was originally used in spyglasses and a ...
that alters the width of the entering beam of light without affecting the divergence of the beam, so they can change the effective focal length 1 to 3 times without increasing
focal ratio In optics, the f-number of an optical system such as a camera lens is the ratio of the system's focal length to the diameter of the entrance pupil ("clear aperture").Smith, Warren ''Modern Optical Engineering'', 4th Ed., 2007 McGraw-Hill Pro ...
. The down side to teleside converters is they will vignette the image on the
wide angle Wide angle may refer to: * Wide-angle lens, type of camera lens * ''Wide Angle'' (TV series), television series * '' Wide Angle'', 1999 album by Hybrid * '' Wide Angles'', 2003 album by Michael Brecker * Wide-angle X-ray scattering * Wide Angle ...
setting if used on a
zoom lens A zoom lens is a mechanical assembly of lens elements for which the focal length (and thus angle of view) can be varied, as opposed to a fixed-focal-length (FFL) lens (see prime lens). A true zoom lens, also called a parfocal lens, is one t ...
. Minimum Focal Length without vignetting will increase inline with higher power of the teleside converter. Before vignetting appears (four black corners), light fall-off will appear first and in general shooting this light fall-off may not be noticeable. The other concern is Minimum Working Distance, so the teleside converter cannot be used below minimum working distance and it depends on both the camera and the teleside converter being used. These types of lenses are used on cameras which lack the facility to change the primary lens and therefore cannot accept a standard rear mount
teleconverter A teleconverter (sometimes called tele extender) is a secondary lens mounted between a camera and a photographic lens which enlarges the central part of an image obtained by the lens. For example, a 2× teleconverter for a 35 mm camera enl ...
, such as consumer and "
prosumer A prosumer is an individual who both consumes and produces. The term is a portmanteau of the words '' producer'' and ''consumer''. Research has identified six types of prosumers: DIY prosumers, self-service prosumers, customizing prosumers, coll ...
"
video camera A video camera is an optical instrument that captures videos (as opposed to a movie camera, which records images on film). Video cameras were initially developed for the television industry but have since become widely used for a variety of oth ...
s and
camcorder A camcorder is a self-contained portable electronic device with video and recording as its primary function. It is typically equipped with an articulating screen mounted on the left side, a belt to facilitate holding on the right side, hot-sw ...
s,
bridge camera Bridge cameras are cameras that fill the niche between relatively simple point-and-shoot cameras and interchangeable-lens cameras such as mirrorless cameras and single-lens reflex cameras (SLRs). They are often comparable in size and weight t ...
s,
point-and-shoot camera A point-and-shoot camera, also known as a compact camera and sometimes abbreviated to P&S, is a still camera designed primarily for simple operation. Most use focus free lenses or autofocus for focusing, automatic systems for setting the exposu ...
s and some older consumer
medium format camera Medium format has traditionally referred to a film format in photography and the related cameras and equipment that use film. Nowadays, the term applies to film and digital cameras that record images on media larger than the used in 135 fil ...
s. Some camera models have specifically designed teleside converters. Since teleside converters are afocal they can be mounted universally on almost any camera lens via adapter rings designed to fit the filter ring of the camera's primary lens.safari-guide.co.uk - Telephoto Conversion Lenses for Bridge Cameras
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See also

*
Secondary lens In photography, a secondary lens or accessory lens is a lens designed to be used in conjunction with another lens, called the ''primary lens''. A secondary lens may be designed to be used either in front of the primary lens, between it and the ...
*
Teleconverter A teleconverter (sometimes called tele extender) is a secondary lens mounted between a camera and a photographic lens which enlarges the central part of an image obtained by the lens. For example, a 2× teleconverter for a 35 mm camera enl ...
*
Convertible lens A camera lens (also known as photographic lens or photographic objective) is an optical lens or assembly of lenses used in conjunction with a camera body and mechanism to make images of objects either on photographic film or on other media capab ...


References


''Scientific photography and applied imaging'' By Sidney F. Ray, page 492


External links


safari-guide.co.uk - Telephoto Conversion Lenses for Bridge Cameras
{{photography subject Photographic lenses