Question

Give the principle,construction and working of a pinhole camera.

Answer 1

 A pinhole camera is a simple camera without a lens and with a single small aperture – effectively a light-proof box with a small hole in one side. Light from a scene passes through this single point and projects an inverted image on the opposite side of the box. The human eye in bright light acts similarly, as do cameras using small apertures. Up to a certain point, the smaller the hole, the sharper the image, but the dimmer the projected image. Optimally, the size of the aperture should be 1/100 or less of the distance between it and the projected image. Because a pinhole camera requires a lengthy exposure, its shutter may be manually operated, as with a flap of light-proof material to cover and uncover the pinhole. Typical exposures range from 5 seconds to several hours. A common use of the pinhole camera is to capture the movement of the sun over a long period of time. This type of photography is called Solargraphy. Pinhole cameras can be handmade by the photographer for a particular purpose. In its simplest form, the photographic pinhole camera can consist of a light-tight box with a pinhole in one end, and a piece of film or photographic paper wedged or taped into the other end. A flap of cardboard with a tape hinge can be used as a shutter. The pinhole may be punched or drilled using a sewing needle or small diameter bit through a piece of tinfoil or thin aluminum or brass sheet. This piece is then taped to the inside of the light tight box behind a hole cut through the box. A cylindrical oatmeal container may be made into a pinhole camera. Pinhole cameras can be constructed with a sliding film holder or back so the distance between the film and the pinhole can be adjusted. This allows the angle of view of the camera to be changed and also the effective f-stop ratio of the camera. Moving the film closer to the pinhole will result in a wide angle field of view and a shorter exposure time. Moving the film farther away from the pinhole will result in a telephoto or narrow angle view and a longer exposure time. Pinhole cameras can also be constructed by replacing the lens assembly in a conventional camera with a pinhole. In particular, compact 35 mm cameras whose lens and focusing assembly has been damaged can be reused as pinhole cameras—maintaining the use of the shutter and film winding mechanisms. As a result of the enormous increase in f-number while maintaining the same exposure time, one must use a fast film in direct sunshine. Pinholes (homemade or commercial) can be used in place of the lens on an SLR. Use with a digital SLR allows metering and composition by trial and error, and is effectively free, so is a popular way to try pinhole photography.[15] Unusual materials have been used to construct pinhole cameras, e.g., a Chinese roast duck. Tank u for asking