Optical properties of photographic lenses, only objects within a limited range of distance from the camera are clearly shown. The process of adapting this series is known as changing the focus of the camera. There are several ways of focusing a camera accurately. The simplest cameras are fixed and use a small aperture and wide angle at all within a certain range of distance of the lens, usually around 3 meters (10 feet) to infinity, is in reasonable focus. Fixed focus cameras are usually cheap species as well as one-use cameras. The camera may be limited focusing range or scale-focus that is indicated in the camera body. The user will guess or calculate the distance to the object and adjust the focus accordingly. On some cameras this is indicated by symbols (head and shoulders facing two people, a tree, mountain).Rangefinder cameras allow the distance to objects to be measured by the combined parallax unit on top of the camera, allowing accurate focus. Single-Lens Reflex cameras allow the photographer to determine the composition of visual focus and lens and to move back to project an image of ground glass or plastic micro-prism screen. Twin-lens reflex cameras use the lens and focus lens unit (usually coincides with the lens.) In the parallel structure of the composition and focusing. View cameras use the ground glass screen which is removed and replaced by either a photographic plate or a reusable holder sheet film before exposure. Modern cameras often offer autofocus systems to focus the camera automatically by a variety of methods, such as fishing.
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