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Internal Focusing
An internal focus lens (sometimes known as IF) is a photographic lens design in which focus is shifted by moving the inner lens group or groups only, without any rotation or shifting of the front lens element. This makes it easy to use, for example, a screwed-in polarizing filter or a petal shaped lens hood. During macro photography, using an internal focus lens reduces the risk of the front of the lens accidentally hitting the subject during focusing as the front element does not move. The physical size of an internal focusing lens does not change during focus, nor does the front of the lens rotate. This is particularly useful for large lenses, keeping the size more compact, or when using filters or accessories mounted on the front of the lens that may require careful alignment. One issue internal focusing lens can have is that the true focal length of the lens is reduced when not focused at infinity. See also * Breathing (lens) Breathing originally referred to any geometric chan ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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 capable of storing an image chemically or electronically. There is no major difference in principle between a lens used for a still camera, a video camera, a telescope, a microscope, or other apparatus, but the details of design and construction are different. A lens might be permanently fixed to a camera, or it might be interchangeable with lenses of different focal lengths, apertures, and other properties. While in principle a simple convex lens will suffice, in practice a compound lens made up of a number of optical lens elements is required to correct (as much as possible) the many optical aberrations that arise. Some aberrations will be present in any lens system. It is the job of the lens designer to balance these and produce a desi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Focus (optics)
In geometrical optics, a focus, also called an image point, is a point where light rays originating from a point on the object converge. Although the focus is conceptually a point, physically the focus has a spatial extent, called the blur circle. This non-ideal focusing may be caused by aberrations of the imaging optics. In the absence of significant aberrations, the smallest possible blur circle is the Airy disc, which is caused by diffraction from the optical system's aperture. Aberrations tend to worsen as the aperture diameter increases, while the Airy circle is smallest for large apertures. An image, or image point or region, is in focus if light from object points is converged almost as much as possible in the image, and out of focus if light is not well converged. The border between these is sometimes defined using a "circle of confusion" criterion. A principal focus or focal point is a special focus: * For a lens, or a spherical or parabolic mirror, it is a point ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Polarizing Filter (Photography)
A polarizing filter or polarising filter (see spelling differences) is often placed in front of the camera lens in photography in order to darken skies, manage reflections, or suppress glare from the surface of lakes or the sea. Since reflections (and sky-light) tend to be at least partially linearly-polarized, a linear polarizer can be used to change the balance of the light in the photograph. The rotational orientation of the filter is adjusted for the preferred artistic effect. For modern cameras, a circular polarizer (CPL) is typically used; this comprises firstly a linear polarizer which performs the artistic function just described, followed by a quarter-wave plate which further transforms the now-linearly polarized light into circularly-polarized light before entering the camera. This additional step avoids problems with autofocus and light-metering sensors within some cameras, which otherwise may not function reliably with a simple linear polarizer. Use Light ref ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Lens Hood
In photography, a lens hood or lens shade is a device used on the front end of a lens to block the Sun or other light source(s) to prevent glare and lens flare. Lens hoods may also be used to protect the lens from scratches and the elements without having to put on a lens cover. The geometry of a lens hood is dependent on three parameters: the focal length of the lens, the size of the front lens element and the dimensions of the image sensor or film in the camera. Cause of lens flare Flare occurs when stray light strikes the front element of a lens and then bounces around within the lens. This stray light often comes from very bright light sources, such as the Sun, bright studio lights, or a bright white background. If a light source is in the lens' angle of view, a lens hood will hardly have any effect, but the light does not have to cause lens flare. It is sufficient that stray light from a bright light source enters the lens. Multi-layer coatings in newer lenses also help t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Macro Lens
Macro photography (or photomacrography or macrography, and sometimes macrophotography) is extreme close-up photography, usually of very small subjects and living organisms like insects, in which the size of the subject in the photograph is greater than life size (though ''macrophotography'' also refers to the art of making very large photographs). By the original definition, a macro photograph is one in which the size of the subject on the negative or image sensor is life size or greater. In some senses, however, it refers to a finished photograph of a subject that is greater than life size. The ratio of the subject size on the film plane (or sensor plane) to the actual subject size is known as the reproduction ratio. Likewise, a macro lens is classically a lens capable of reproduction ratios of at least 1:1, although it often refers to any lens with a large reproduction ratio, despite rarely exceeding 1:1. Apart from technical photography and film-based processes, where the s ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Breathing (lens)
Breathing originally referred to any geometric change in field-of-view when changing focus distance. Even if the angle-of-view is constant distortion changes will cause visible breathing. It has been recently used by photographers for changes of focal length of a lens when changing the focus. Breathing is sometimes used for the suction and expulsion of air from within the lens as its internal volume changes. A lens with a constant focal length will exhibit narrowing of the angle of view at closer focus, and conversely, maintaining a constant angle of view requires precise reduction of focal length as focus is decreased, which some (often higher quality) lenses are designed to do. Lens breathing does not prevent one from racking focus A focus puller or first assistant camera (1st AC) is a member of a film crew's camera department whose primary responsibility is to maintain the camera lens's optical focus on whatever subject or action is being filmed. "Pulling focus" refers to ... o ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
