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Focus (optics) Eye focusing ideally collects all light rays from a point on an object into a corresponding point on the retina. A demonstration of camera focus on different distances, showing a bamboo rooftop. Text on a page that is partially in focus, but mostly not in varying degrees. In geometrical optics, a focus, also called an image point ...
Focal length. The focal point F and focal length f of a positive (convex) lens, a negative (concave) lens, a concave mirror, and a convex mirror. 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 ...
Fixed-focus lens. The back of an iPhone 3G, showing its small fixed-focus lens. Mid-20th-century medium-format fixed-focus camera. A photographic lens for which the focus is not adjustable is called a fixed-focus lens or sometimes focus-free. The focus is set at the time of lens design, and remains fixed. It is usually set to the hyperfocal ...
In optics and photography, hyperfocal distance is a distance from a lens beyond which all objects can be brought into an "acceptable" focus. As the hyperfocal distance is the focus distance giving the maximum depth of field, it is the most desirable distance to set the focus of a fixed-focus camera. [1] The hyperfocal distance is entirely ...
Depth of field is the front-to-back range of focus in an image, or how much of it appears sharp and clear. In deep focus, the foreground, middle ground, and background are all in focus. Deep focus is normally achieved by choosing a small aperture. Since the aperture of a camera determines how much light enters through the lens, achieving deep ...
Follow focus. An Arri 35mm film camera with a follow focus mechanism mounted to a zoom lens. Pulling focus using a follow focus device. A follow focus is a focus control mechanism used in filmmaking with film cameras and in television production with professional video cameras. It is ergonomic rather than strictly necessary; in other words it ...
Zoom lenses (sometimes referred to as "true" zoom) are ideally parfocal, in that focus is maintained as the lens is zoomed (i.e., focal length and magnification changed), which is convenient and has the advantage of allowing more accurate focusing at maximal focal length then zooming back to a shorter focal length to compose the image.
A collection of telephoto lenses. A telephoto lens, also known as telelens, is a specific type of a long-focus lens used in photography and cinematography, in which the physical length of the lens is shorter than the focal length. [1] : 93 This is achieved by incorporating a special lens group known as a telephoto group that extends the light ...