A pinhole camera is a light-proof box with a small hole in the centre of one side.
What is pinhole camera?The simple answer to 'what is a pinhole camera?' is that it is the simplest device one can use to take photographs. Pinhole camera is a light-tight box with a pinhole on one side through which light enters and a reversed and inverted image is cast on the side opposite to the hole on the rear-side or photo film. Normally pinhole device does not have any lens and through a small hole light reflected off the object travels in rectilinear propagation principle and reaches the rear end (opposite to the pinhole) of the box. In our daily life we come across the example of these images but we hardly notice it.
Light falling through the canopy of leaves is very good example especially during solar eclipse when we can clearly see a number of crescent shaped images of sun cast on the ground through the leaves of trees. This has been observed from ancient times and in fifth century BC Mo Ti, a Chinese philosopher has recorded these effects. The size of the hole (aperture) makes a big difference on the type of image.
The smaller the better. However there is a critical smallness in size for the hole beyond which the images fade and goes out of focus. Light, though has rectilinear propagation, is essentially a wave like phenomenon and diffraction of light occurs when the hole is very small. The required optical diameter for the aperture has been calculated for achieving the sharpest images possible. In this photography optimally the size of the aperture should be less than 1/100 of the distance between the aperture and the image screen.
The hole must be perfectly round and the material on which the hole is punched must be very thin in order to reduce diffraction and vignetting of images. The shutter is usually operated manually in this type of photography. The special characteristic of the images are their uneven exposure. It captures wide angle of scenery and this results in light taking longer time to reach the edges than the centre. The edges of the images get darkened due to under exposure in photography which adds an unique beauty to the images. Another characteristics of pinhole photography is that the depth of field is infinite and near and far objects being captured with same equal sharpness. In the modern days, pinhole camera photography has taken special place in spacecraft photography and space photography as well as use in spy camera to obtain discrete images. There are certain limitations in this photography like knowing the exact exposure time. In this photography, aperture adjustments for moving objects and variance of light intensity for images also have limitations. Special features can be build in to the pinhole device like simultaneous exposure with multiple holes and special effects photography by curving the image screen. Construction of pinhole camera is very easy and can be made from household boxes of various sizes.