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 splitters.[1] The name pellicle is a diminutive of pellis, a skin or film.
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.[2]
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 colors. 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 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.[3]
The first camera to employ the pellicle mirror as a beam splitter for the viewfinder was the Canon Pellix, 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 RE Super. That employed a CdS 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.[4] The Pellix pellicle mirror was an ultra-thin (0.02mm) 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.[5]
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.[5] In 1984, Canon released another version of their then "New F-1", which attained a record 14 frames per second performance, being the fastest analog SLR of that time.
Nippon Kogaku KK, Japan introduced their high-speed Nikon F2H 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 and has a non-removable Type B focusing screen.[6]
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/EOS 630 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 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 has introduced cameras with plastic[7] pellicle-like mirrors, which it describes as "Single-Lens Translucent" cameras.[8] These cameras divert a portion of incoming light to a phase-detection autofocus unit, while the remaining light strikes a digital image sensor. Sony "SLT" cameras employ an electronic viewfinder (EVF) allowing exposure value, white balance and other settings to be verified and adjusted visually before taking a picture, although typically the EVF displays far less dynamic range 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.
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-stop loss of light at the receptor, and a corresponding 2-stop loss of light in the viewfinder
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.
A single-lens reflex camera (SLR) is a camera that typically uses a mirror and prism system that permits the photographer to view through the lens and see exactly what will be captured. With twin lens reflex and rangefinder cameras, the viewed image could be significantly different from the final image. When the shutter button is pressed on most SLRs, the mirror flips out of the light path, allowing light to pass through to the light receptor and the image to be captured.
A digital single-lens reflex camera is a digital camera that combines the optics and the mechanisms of a single-lens reflex camera with a digital imaging sensor.
The Nikon F3 was Nikon's third professional single-lens reflex camera body, preceded by the F and F2. Introduced in 1980, it had manual and semi-automatic exposure control whereby the camera would select the correct shutter speed. The Nikon F3 series cameras had the most model variations of any Nikon F camera. It was also the first of numerous Nikon F-series cameras to be styled by Italian designer Giorgetto Giugiaro, and to include a red stripe on the handgrip – a feature that would later become a signature feature of many Nikon cameras.
The Canon A-1 is an advanced level single-lens reflex (SLR) 35 mm film camera for use with interchangeable lenses. It was manufactured by Canon Camera K. K. in Japan from April 1978 to 1985. It employs a horizontal cloth-curtain focal-plane shutter with a speed range of 30 to 1/1000 second plus bulb and flash synchronization speed of 1/60 second. It has dimensions of 92 millimetres (3.6 in) height, 141 millimetres (5.6 in) width, 48 millimetres (1.9 in) depth and 620 grams (22 oz) weight. Unlike most SLRs of the time, it was available in only one color; all black. The introductory US list price for the body plus Canon FD 50 mm f/1.4 SSC lens was $625, the camera was generally sold with a 30–40% discount.
Advanced Photo System type-C (APS-C) is an image sensor format approximately equivalent in size to the Advanced Photo System film negative in its C ("Classic") format, of 25.1×16.7 mm, an aspect ratio of 3:2. It is therefore also equivalent in size to the Super 35 motion picture film format, which has the dimensions of 24.89 mm × 18.66 mm.
In photography, through-the-lens (TTL) metering refers to a feature of cameras whereby the intensity of light reflected from the scene is measured through the lens; as opposed to using a separate metering window or external hand-held light meter. In some cameras various TTL metering modes can be selected. This information can then be used to set the optimal film or image sensor exposure, it can also be used to control the amount of light emitted by a flash unit connected to the camera.
A full-frame DSLR is a digital single-lens reflex camera (DSLR) with a 35 mm image sensor format. Historically, 35 mm was considered a small film format compared with medium format, large format and even larger.
The Canon F-1 is a 35 mm single-lens reflex camera produced by Canon of Japan from March 1971 until the end of 1981, at which point it had been superseded by the New F-1 launched earlier that year. The Canon FD lens mount was introduced along with the F-1, but the previous Canon FL-mount lenses and older R- series lenses were also compatible with the camera with some limitations. The Canon F-1 was marketed as a competitor to the Nikon F and Nikon F2 single lens reflex cameras by Nikon.
The Canon FT QL is a 35mm single-lens reflex camera introduced by Canon Inc. in March 1966. It has a Canon FL lens mount compatible with the large range of FL series lenses. The FT can also operate the later Canon FD series lenses in stop-down mode, but the earlier R series has a different lens aperture mechanism and cannot be used, although the bayonet fitting is similar. The standard kit lenses were Canon's 50mm f/1.8 ; 50mm f/1.4 and 58mm f/1.2, the body-only option was offered later.
The history of the single-lens reflex camera (SLR) begins with the use of a reflex mirror in a camera obscura described in 1676, but it took a long time for the design to succeed for photographic cameras: the first patent was granted in 1861, and the first cameras were produced in 1884 but while elegantly simple in concept, they were very complex in practice. One by one these complexities were overcome as optical and mechanical technology advanced, and in the 1960s the SLR camera became the preferred design for many high-end camera formats.
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, so the EOS RT was technically "out of production" before it ever went on sale.
The EOS-1N is a 35mm single lens reflex (SLR) camera body produced by Canon. It was announced by Canon in 1994, and was the professional model in the range, superseding the original EOS-1. The camera was itself superseded by the EOS-1v in 2000.
The Canon Pellix is a manual focus camera released in 1965 that uses a semitransparent stationary reflex mirror behind which a metering cell is raised during the reading.
Live preview is a feature that allows a digital camera's display screen to be used as a viewfinder. This provides a means of previewing framing and other exposure before taking the photograph. In most such cameras, the preview is generated by means of continuously and directly projecting the image formed by the lens onto the main image sensor. This in turn feeds the electronic screen with the live preview image. The electronic screen can be either a liquid crystal display (LCD) or an electronic viewfinder (EVF).
This article is about photographic lenses for single-lens reflex film cameras (SLRs) and digital single-lens reflex cameras (DSLRs). Emphasis is on modern lenses for 35 mm film SLRs and for DSLRs with sensor sizes less than or equal to 35 mm ("full-frame").
The Canon EOS 500D is a 15-megapixel entry-level digital single-lens reflex camera, announced by Canon on 25 March 2009. It was released in May 2009. It is known as the EOS Kiss X3 in Japan, and as the EOS Rebel T1i in North America. It continues the Rebel line of mid-range DSLR cameras, is placed by Canon as the next model up from the EOS 450D, and has been superseded by the EOS 550D (T2i).
A mirrorless interchangeable-lens camera (MILC) or simply mirrorless camera, also called digital single lens mirrorless (DSLM), is a photo camera featuring a single, removable lens and a digital display. The camera does not have a reflex mirror or optical viewfinder like a digital single-lens reflex (DSLR) camera. Many mirrorless cameras retain a mechanical shutter. Like a DSLR, a mirrorless camera accepts any of a series of interchangeable lenses compatible with its lens mount.
Single-lens translucent (SLT) is a Sony proprietary designation for Sony Alpha cameras which employ a pellicle mirror, electronic viewfinder, and phase-detection autofocus system. They employ the same Minolta A-mount as Sony Alpha DSLR cameras.
The Sony α77 was the flagship for Sony's midrange Alpha SLT camera line.
The Sony Alpha 99 was announced by Sony on September 12, 2012. It was the flagship Sony DSLR camera and of the Sony Alpha SLT line until late 2016 when it was replaced by the Sony α99 II.
References
↑ Eric P. Goodwin, James C. Wyant (2006). "Plate and Pellicle Beamsplitters". Fundamentals of Interferometry. SPIE Press Book. p.8. ISBN978-0-8194-6510-8.
↑ Roger Hicks (1984). A history of the 35mm Still Camera. Focal Press. ISBN0-240-51233-2.
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