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

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 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.[16]

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please give thumbs up

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 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.

http://upload.wikimedia.org/wikipedia/commons/thumb/3/3b/Pinhole-camera.svg/220px-Pinhole-camera.svg.png

Find or Build the Camera Body: Shown here is one-half of a cardboard box that has an identical shaped lid slightly larger for a snug fit. Note: shallow lids tend to leak light. Generally, you will want your camera body to be light-tight. When you look for a potential container, it should be easy to open and close. This is important if you plan to use the camera to make more than a few photographs. Select a material that paint adheres to easily. Cardboard or wood is a good choice. For metal lightly sanding will help the paint to adhere and not flake off. While metal such as a cookie tin, will not leak light, it is still a good idea to paint the inside because of reflections. Using a container with a plastic lid can lead to difficulties because repeated bending may cause the the paint to crack and leak light.

 

 http://pinhole.us/pinhole_info/pinhole_images/cbrush.gif

 http://pinhole.us/pinhole_info/pinhole_images/cpaint.gif


Darken the Camera Body:
 Paint the interior of the camera body. You will probably need to paint more than one coat to make the camera light-tight. Usually, I prefer latex, flat black paint out of a can rather that spray paint. Between each application, allow the paint to dry completely. Later, when testing your camera, if you find a small light leak you can use the black tape listed below.

 brass or metal piece


Aperture Plate:
 Next you will need some thin metal for the pinhole aperture. Although I use paper-thin, brass shim stock obtained from an automotive supply store you may substitute a piece of aluminum from a beverage can.

       

 

 http://pinhole.us/pinhole_info/pinhole_images/cpush.gif

Piercing a hole or aperture: Place the metal on a flat surface with wood or matt board underneath while piercing. I use a push pin to make a small hole for the aperture. Start by gently piercing a tiny hole. This creates a burr (raised metal around the edge of the hole) on the opposite side. Using fine sandpaper, remove the burr. Enlarge the hole with the push pin and repeat this procedure until the desired size of the hole is reached. Trying to create the full diameter of the hole at one time will result in a less than perfect circle. For smaller size holes work slowly and carefully. Paint the back side of the aperture plate. After the paint is dry, use the push pin to carefully clear the aperture of paint if necessary.


Aperture Size: There is an ideal size aperture for each camera'sfocal length (the distance of the aperture to the back of the camera where the film lies). However, it is possible to work simply. For example if the depth of the container - focal length - is 12 inches make your aperture the maximum diameter of the push pin. For smaller cameras, use the point of the push pin. For larger cameras you may use a drill bit. In fact, drill bits are one option used by some which create a hole with a known size based on the diameter of the bit. Jewelers bits come in very small sizes. There are drilled pinholes available in different sizes. I would recommend knowing your aperture size if you are planning to expose film instead of B&W paper for your negatives. A micrometer can also be used to measure the needle or instrument you make the aperture with.

 http://pinhole.us/pinhole_info/pinhole_images/ctape.gif

Cut a hole just smaller than the size of your aperture plate. 
Using black masking or electrical tape, attach the aperture to the front of the camera. For a shutter simply use a small piece of black tape over the aperture. Note: electrical tape works but in time (or hot weather) it deteriorates much faster than masking tape.

 

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hey u copied from wiki pedia thats cheating

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