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| Camera |
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| Construction |
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| A photographic camera consists of a converging lens system at least one end of a box and a light sensitive film at the other end, a focusing device for adjusting the distance of the lens from the film and an exposure arrangement which provides the correct exposure. The object is placed in such a way that a real inverted image of the object is formed on the film. The amount of light entering the film region can be adjusted by adjusting the aperture of the lens. |
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| The lens system contains an achromatic doublet and separated lenses, which can minimize chromatic aberration. The box is painted black inside to avoid unnecessary reflection inside. |
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| A shutter is placed between the lens and the film. When a photograph is taken, the shutter opens and closes quickly, thereby exposing the film to light for a short time to light entering the camera. The sensitive photographic film is coated with a chemical emulsion of silver halogen compound, which is very sensitive to light. The film is mounted with the help of film spooks. |
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| A sharp image of the object is focused on the film by adjusting the distance of the lens from the film. There is a focusing ring, which turns over a scale engraved on the lens. By means of this ring, the distance between the lens and the film can be adjusted by moving the lens forward and backwards. |
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| The film speed is a measure of how quickly the film will be exposed when in use. A fast film needs a relatively short time exposure while a slow speed film needs somewhat longer time. |
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| Most of the cameras have a viewfinder, which helps the user to see what the camera sees before exposing the film. |
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| The lens aperture is generally expressed as the fraction of focal length 'f of the lens. When the lens is focused for a certain distance, the different parts of the object at that distance are sharp and the other points look blurred circles called the 'circles of confusion'. |
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| Many cameras have built in exposure meters, having light sensitive surfaces. A current flows in the meter depending on the amount of light falling on it. So, the photographer has to adjust a suitable set of aperture and exposure times for correct exposure. |
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| There is also another aspect called as 'the depth of focus'. When the aperture is large, the image is not focused in a single plane but gets spread out. The depth of focus indicates the range of the object distances. |
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