Pellicle mirror
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A pellicle mirror is an ultra-thin, ultra-lightweight semi-transparent mirror employed in the light path of an optical instrument, splitting the light beam into two separate beams, both of reduced light intensity. Splitting the beam allows its use for multiple purposes simultaneously. The thinness of the mirror practically eliminates beam or image doubling due to a non-coincident weak second reflection from the nominally non-reflecting surface, a problem with mirror-type
beam splitter A beam splitter or ''beamsplitter'' is an optical device that splits a beam of light into a transmitted and a reflected beam. It is a crucial part of many optical experimental and measurement systems, such as interferometers, also finding wide ...
s. The name ''pellicle'' is a diminutive of ''pellis'', a skin or film.


In photography

In photography, the pellicle mirror has been employed in single-lens reflex (SLR) cameras, at first to enable through-the-lens exposure measurement and possibly to reduce camera shake, but later most successfully to enable fast series photography, which otherwise would be slowed down by the movement of the reflex mirror, while maintaining constant finder vision. The first use of pellicle mirrors for consumer photography however were in color separation cameras. The Devin Tricolor Camera from at least the 1938 version used two pellicle mirrors plus three color filters to split the image from a single lens into three images of the three additive primary color

Pellicle mirrors are ideal for this purpose, even today, since they are lighter and cheaper than an optical block of dichroic prisms, which would be heavy and expensive for large, high resolution film or plates. The conventional
SLR camera A single-lens reflex camera (SLR) 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. With twin le ...
has a reflex mirror directing the light beam from the lens to the focusing screen in the viewfinder, which is swung out of the light path when the exposure is made and causing the viewfinder to go dark. This action adds a delay between pressing the shutter release and the actual exposure of the film. The first camera to employ the pellicle mirror as a beam splitter for the viewfinder was the
Canon Pellix The Canon Pellix is a manual-focus single-lens reflex (SLR) camera released in 1965 that uses a stationary half-silvered mirror behind which a metering cell is raised during light level metering. The First Canon with TTL Canon suddenly switche ...
, launched by Canon Camera Company Inc. Japan in 1965. The object was to accomplish exposure measurement through the lens (TTL), which was pioneered by Tokyo Kogaku KK, Japan in the 1963
Topcon is a Japanese manufacturer of optical equipment for ophthalmology and surveying. History September 1932—TOPCON was established based on the surveying instruments division of K. Hattori & Co., Ltd. (currently SEIKO HOLDINGS CORPORATION) in or ...
RE Super. That employed a
CdS The compact disc (CD) is a digital optical disc data storage format that was co-developed by Philips and Sony to store and play digital audio recordings. In August 1982, the first compact disc was manufactured. It was then released in Octo ...
meter cell placed behind the reflex mirror that had narrow slits cut into the surface to let the light reach the cell. Canon improved on the idea by making the mirror semi-translucent and fixed. The meter cell was swung into the light-path behind the mirror by operating a lever on the right-hand camera front for stopped down exposure reading, momentarily dimming the viewfinder. Two thirds of the light from the camera lens was let through the mirror, while the rest was reflected up to the viewfinder screen. The Pellix pellicle mirror was an ultra-thin (0.02 mm) Mylar film with a vapour deposited semi reflecting layer. Since there was no mirror blackout, the user could see the image at the moment of exposure. The next 35mm SLR camera to employ the pellicle mirror was the Canon F-1 High Speed, made available in the event of the 1972 Olympic games, the object being rapid series photography, difficult at the time to obtain with a moving mirror. The mirror design was the same as in the Pellix. In 1984, Canon released another version of their then "New F-1", which attained a record 14
frames per second A frame is often a structural system that supports other components of a physical construction and/or steel frame that limits the construction's extent. Frame and FRAME may also refer to: Physical objects In building construction *Framing (con ...
performance, being the fastest analog SLR of that time. Nippon Kogaku KK, Japan introduced their high-speed
Nikon F2 The Nikon F2 is a professional-level, interchangeable lens, 35mm format, 35 mm film, single-lens reflex (SLR) camera. It was manufactured by the Japanese optics company Nippon Kogaku K. K. (Nikon Corporation since 1988) in Japan from September 1 ...
H in 1976. The mirror is a pellicle rather than a conventional front surfaced mirror that swings out of the light path when the exposure is made. To identify the F2H, note the shutter speed dial has no T, B or 1/2000; has no
self-timer A self timer is a device on a camera that gives a delay between pressing the shutter release and the shutter's firing. It is most commonly used to let the photographer to take a photo of themselves (often with a group of other people), hence t ...
and has a non-removable Type B focusing screen. Two further Canon models were produced with pellicle mirrors, the EOS RT and the EOS-1N RS, the RT being based on the
EOS 600 In ancient Greek mythology and Ancient Greek religion, religion, Eos (; Ionic Greek, Ionic and Homeric Greek ''Ēṓs'', Attic Greek, Attic ''Héōs'', "dawn", or ; Aeolic Greek, Aeolic ''Aúōs'', Doric Greek, Doric ''Āṓs'') is the godd ...
/
EOS 630 In ancient Greek mythology and religion, Eos (; Ionic and Homeric Greek ''Ēṓs'', Attic ''Héōs'', "dawn", or ; Aeolic ''Aúōs'', Doric ''Āṓs'') is the goddess and personification of the dawn, who rose each morning from her home ...
and the 1N RS being based on the EOS-1N. As development of SLR cameras has progressed since these early models, fast sequence shooting has apparently become possible using ordinary moving mirrors in high-speed cameras, getting rid of the vulnerable pellicle mirror that was prone to dust and dirt. The mirror mechanism of conventional SLR cameras has improved since the Pellix mirror was introduced; the viewfinder is dark for only a very short time, the
shutter lag In photography, shutter lag is the delay between triggering the shutter and when the photograph is actually recorded. This is a common problem in the photography of fast-moving objects or animals and people in motion. The term narrowly refers only t ...
is small, and the mirror-return is fast enough for rapid shooting. Digital SLR cameras are able to take ten frames or more per second employing an instant-return mirror.


Sony SLT concept

Sony has introduced cameras with plastic pellicle-like mirrors, which it describes as "Single-Lens Translucent" cameras. These cameras divert a portion of incoming light to a phase-detection
autofocus An autofocus (or AF) optical system uses a sensor, a control system and a motor to focus on an automatically or manually selected point or area. An electronic rangefinder has a display instead of the motor; the adjustment of the optical system ...
unit, while the remaining light strikes a digital
image sensor An image sensor or imager is a sensor that detects and conveys information used to make an image. It does so by converting the variable attenuation of light waves (as they pass through or reflect off objects) into signals, small bursts of curr ...
. Sony "SLT" cameras employ an
electronic viewfinder An electronic viewfinder (EVF) is a camera viewfinder where the image captured by the lens is displayed on a small screen (usually LCD or OLED) which the photographer can look through when composing their shot. It differs from a live preview sc ...
(EVF) allowing
exposure value In photography, exposure value (EV) is a number that represents a combination of a camera's shutter speed and f-number, such that all combinations that yield the same exposure have the same EV (for any fixed scene luminance). Exposure value is a ...
,
white balance In photography and image processing, color balance is the global adjustment of the intensities of the colors (typically red, green, and blue primary colors). An important goal of this adjustment is to render specific colors – particularly neu ...
and other settings to be verified and adjusted visually before taking a picture, although typically the EVF displays far less
dynamic range Dynamic range (abbreviated DR, DNR, or DYR) is the ratio between the largest and smallest values that a certain quantity can assume. It is often used in the context of signals, like sound and light. It is measured either as a ratio or as a base-1 ...
than the sensor. The refresh rate of the viewfinder is limited by the time it takes the sensor to make a usable exposure; thus in low light the frame rate of the viewfinder may be as low as four frames per second. "SLT" cameras also lack a real-time view at high shooting rates, when the viewfinder shows the last picture taken instead of the one being taken — a phenomenon comparable to certain older SLRs that can only achieve their maximum burst rate in
mirror lock-up Mirror lock-up (often abbreviated to MLU) is a feature employed in many Single Lens Reflex (SLR) cameras. It allows the operator to reduce vibration-induced motion blur during exposure. It also allows the mounting of lenses which extend into th ...
.


Motion-picture cameras

Few film movie cameras have been made that make use of the pellicle mirror. Probably the earliest is the Pathé WEBO M, m for membrane, of 1946. With that camera light is reflexed sideways into a primary plano-convex finder lens, the plane side being partially or fully matted. Another French amateur movie camera with a pellicle is the Christen Reflex for Double-Eight film. It was made from 1960 on and provides a lightly slanted deflection. Later, in 1967, the professional Mitchell NCR and BNCR cameras were equipped with a pellicle-based finder. In the Soviet Union in 1970 appeared the Kiev 16 Alpha, also featuring a pellicle mirror finder system that deflects strictly vertically.


Advantages and disadvantages

Advantages of a pellicle mirror: * The user has an uninterrupted view through the viewfinder while making an exposure. * There is no vibration from mirror movement, reducing shake and audible noise. At the same time, the system is devoid of play or backlash. * Shutter lag may be diminished, and pictures taken at a faster rate, compared to systems employing a reflex mirror. * Continuous phase-detection autofocus during video, live view or continuous shooting mode. Disadvantages of a pellicle mirror: * The pellicle mirror causes an up to 1/3-
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loss of light at the receptor, and a corresponding 2-
stop Stop may refer to: Places * Stop, Kentucky, an unincorporated community in the United States * Stop (Rogatica), a village in Rogatica, Republika Srpska, Bosnia and Herzegovina Facilities * Bus stop * Truck stop, a type of rest stop for truck d ...
loss of light in the
viewfinder In photography, a viewfinder is what the photographer looks through to compose, and, in many cases, to focus the picture. Most viewfinders are separate, and suffer parallax, while the single-lens reflex camera lets the viewfinder use the main ...
* The mirror has to be kept perfectly clean, or the light sensor and other electronics (as well as the image quality) will suffer. * Owing to its thinness, the pellicle mirror is fragile, making it difficult to clean. * As the viewfinder does not go dark, there is no visual indication that the shutter has fired. This could be a problem in a noisy environment where the shutter cannot be heard.


Cameras

* Devin Colorgraph Company ** Devin Tricolor Camera (1938) * Canon **
Canon Pellix The Canon Pellix is a manual-focus single-lens reflex (SLR) camera released in 1965 that uses a stationary half-silvered mirror behind which a metering cell is raised during light level metering. The First Canon with TTL Canon suddenly switche ...
(1965) ** Canon Pellix QL (1966) ** Canon F-1 High Speed Motor Drive (for the
1972 Winter Olympics The 1972 Winter Olympics, officially the and commonly known as Sapporo 1972 ( ja, 札幌1972), was a winter multi-sport event held from February 3 to 13, 1972, in Sapporo, Japan. It was the first Winter Olympic Games to take place outside Europe ...
) ** Canon New F-1 High Speed Motor Drive (for the
1984 Summer Olympics The 1984 Summer Olympics (officially the Games of the XXIII Olympiad and also known as Los Angeles 1984) were an international multi-sport event held from July 28 to August 12, 1984, in Los Angeles, California, United States. It marked the secon ...
) **
Canon EOS RT The Canon EOS RT is a 35mm single-lens reflex camera produced by Canon and sold from 1989 to 1992. The camera is essentially an EOS 630/ EOS 600 with a pellicle mirror. Only 25,000 were manufactured at the end of the EOS 630 production run, ...
(1989) ** Canon EOS-1N RS (1994) * Nikon ** Nikon F High Speed (1976)Cameraquest – Nikon F 7 fps High Speed
/ref> ** Nikon F2H (1978) ** Nikon F3H (for the
1998 Nagano Olympics The 1998 Winter Olympics, officially known as the and commonly known as Nagano 1998 ( ja, 長野1998), was a winter multi-sport event held from 7 to 22 February 1998, mainly in Nagano, Japan, with some events taking place in the ...
) * Sony ** Sony α33 (SLT-A33) (2010) ** Sony α35 (SLT-A35) (2011) ** Sony α37 (SLT-A37) (2012) ** Sony α55 (SLT-A55) / Sony α55V (SLT-A55V) (2010) ** Sony α57 (SLT-A57) (2012) ** Sony α58 (SLT-A58) (2013) ** Sony α65 (SLT-A65) / Sony α65V (SLT-A65V) (2011) ** Sony α68 (ILCA-68) (2015) ** Sony α77 (SLT-A77) / Sony α77V (SLT-A77V) (2014) ** Sony α77 II (ILCA-77M2) (2014) ** Sony α99 (SLT-A99) / Sony α99V (SLT-A99V) (2012) ** Sony α99 II (ILCA-99M2) (2016)


References

{{Pellicle mirror film cameras Camera features Mirrors