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Reflex Finder
A reflex finder is a viewfinder system with a mirror placed behind a lens. The light passing through the lens is reflected by the mirror to a focusing screen, usually ground glass. The image formed on this ground glass can be observed directly, giving a ''waist-level reflex finder,'' or through a redressing optical device (set of mirrors or prism) for eye-level viewing, giving an ''eye-level reflex finder''. With a reflex finder, you can focus the image on the ground glass and frame your picture at the same time. It is common to find a device on the center of the ground glass to help precise focusing, for example a split-image or a microprism device. Today's reflex cameras usually incorporate autofocusing. Reflex finders are found in: * Single-lens reflex (SLR) cameras, with one lens for both viewing and taking the picture * Twin-lens reflex A twin-lens reflex camera (TLR) is a type of camera with two objective lenses of the same focal length. One of the lenses is the photo ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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 optical system. Viewfinders are used in many cameras of different types: still and movie, film, analog and digital. A zoom camera usually zooms its finder in sync with its lens, one exception being rangefinder cameras. History Before the development of microelectronics and electronic display devices, only optical viewfinders existed. Direct optical viewfinders Direct viewfinders are essentially miniature Galilean telescopes; the viewer's eye was placed at the back, and the scene viewed through the viewfinder optics. A declining minority of point and shoot cameras use them. Parallax error results from the viewfinder being offset from the lens axis, to point above and usually to one side of the lens. The error varies with distance, being ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Lens (optics)
A lens is a transmissive optical device which focuses or disperses a light beam by means of refraction. A simple lens consists of a single piece of transparent material, while a compound lens consists of several simple lenses (''elements''), usually arranged along a common axis. Lenses are made from materials such as glass or plastic, and are ground and polished or molded to a desired shape. A lens can focus light to form an image, unlike a prism, which refracts light without focusing. Devices that similarly focus or disperse waves and radiation other than visible light are also called lenses, such as microwave lenses, electron lenses, acoustic lenses, or explosive lenses. Lenses are used in various imaging devices like telescopes, binoculars and cameras. They are also used as visual aids in glasses to correct defects of vision such as myopia and hypermetropia. History The word ''lens'' comes from '' lēns'', the Latin name of the lentil (a seed of a lentil plant), ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Focusing Screen
A focusing screen is a flat translucent material, either a ground glass or Fresnel lens, found in a system camera that allows the user of the camera to preview the framed image in a viewfinder. Often, focusing screens are available in variants with different etched markings for various purposes. For instance, "overall matte" focusing screens with no etchings are a popular choice for astrophotography and other low-light situations. Overview The history of the focusing screen is almost as long as the history of the camera. Some primitive cameras consisted of a box with a board holding the lens in the front and a focusing screen in the back that was replaced by the imaging medium (plate, film holder) before taking the picture. The most common type of focusing screen in non-autofocus 35 mm SLR cameras is the split screen and microprism ring variation that aids focusing and became standard in the 1980s. The microprism ring breaks up the image unless the lens setting is in focu ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ground Glass
Ground glass is glass whose surface has been ground to produce a flat but rough (matte) finish, in which the glass is in small sharp fragments. Ground glass surfaces have many applications, ranging from ornamentation on windows and table glassware to scientific uses in optics and laboratory glassware. Uses Photography In photography, a sheet of ground glass is used for the manual focusing in some still and movie cameras; the ground-glass viewer is inserted in the back of the camera, and the lens opened to its widest aperture. This projects the scene on the ground glass upside down. The photographer focuses and composes using this projected image, sometimes with the aid of a magnifying glass (or loupe). In order to see the image better, a dark cloth is used to block out light, whence came the image of the old-time photographer with his head stuck under a large black cloth. A ground glass is also used in the reflex finder of an SLR or TLR camera. In motion-picture cameras, t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Split-image Focusing Screen
A focusing screen is a flat translucent material, either a ground glass or Fresnel lens, found in a system camera that allows the user of the camera to preview the framed image in a viewfinder. Often, focusing screens are available in variants with different etched markings for various purposes. For instance, "overall matte" focusing screens with no etchings are a popular choice for astrophotography and other low-light situations. Overview The history of the focusing screen is almost as long as the history of the camera. Some primitive cameras consisted of a box with a board holding the lens in the front and a focusing screen in the back that was replaced by the imaging medium (plate, film holder) before taking the picture. The most common type of focusing screen in non-autofocus 35 mm SLR cameras is the split screen and microprism ring variation that aids focusing and became standard in the 1980s. The microprism ring breaks up the image unless the lens setting is in focu ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Autofocusing
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 has to be done manually until indication. Autofocus methods are distinguished as active, passive or hybrid types. Autofocus systems rely on one or more sensors to determine correct focus. Some AF systems rely on a single sensor, while others use an array of sensors. Most modern SLR cameras use through-the-lens optical sensors, with a separate sensor array providing light metering, although the latter can be programmed to prioritize its metering to the same area as one or more of the AF sensors. Through-the-lens optical autofocusing is usually speedier and more precise than manual focus with an ordinary viewfinder, although more precise manual focus can be achieved with special accessories such as focusing magnifiers. Autofocus accuracy ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Single-lens Reflex 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 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. History File:Hasselblad 1600F.jpg, Medium format SLR by Hasselblad (Model 1600F), Sweden File:Zenza BRONICA S2 with ZENZANON 100mm F2.8.JPG, Medium format SLR by Bronica (Model S2), Japan. Bronica's later model—the Bronica EC—was the first medium format SLR camera to use an electrically operated focal-plane shutter File:Asahiflex600.jpg, The 1952 (Pentax) Asahiflex, Japan's first single-lens reflex camera. File:Contaflex BW 2.JPG, The Contaflex III a single- ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Twin-lens Reflex Camera
A twin-lens reflex camera (TLR) is a type of camera with two objective lenses of the same focal length. One of the lenses is the photographic objective or "taking lens" (the lens that takes the picture), while the other is used for the viewfinder system, which is usually viewed from above at waist level. In addition to the objective, the viewfinder consists of a 45-degree mirror (the reason for the word ''reflex'' in the name), a matte focusing screen at the top of the camera, and a pop-up hood surrounding it. The two objectives are connected, so that the focus shown on the focusing screen will be exactly the same as on the film. However, many inexpensive 'pseudo' TLRs are fixed-focus models. Most TLRs use leaf shutters with shutter speeds up to 1/500 of a second with a bulb setting. For practical purposes, all TLRs are film cameras, most often using 120 film, although there are many examples which used 620 film, 127 film, and 35 mm film. Few general-purpose digital TLR cam ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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