Pinhole Camera

The word camera comes from the Greek kamara, a vaulted chamber. A pinhole camera is the simplest camera possible. It consists of a light-proof box, some sort of film and a pinhole. The pinhole is simply an extremely small hole like you would make with the tip of a pin in a piece of thick aluminium foil. 

A pinhole camera works on a simple principle. 
Imagine you are inside a large, dark, room-sized box containing a pinhole. Imagine that outside the room is a friend with a flashlight, and he is shining the flashlight at different angles through the pinhole. When you look at the wall opposite the pinhole, what you will see is a small dot created by the flashlight’s beam shining through the pinhole. The small dot will move as your friend moves his flashlight. The smaller the pinhole (within limits), the smaller and sharper the point of light that the flashlight creates.

Rays scatter off objects in all directions. The pinhole in the front of the camera selects only the rays traveling in the direction of the pinhole. These rays pass into the camera and strike the back surface.The front and side walls shade that point on the back from rays coming from different points of origin.

A pinhole camera casts an inverted image on the back. This image will also be slightly blurry, because light coming from one atom on the object spreads out over the back of the camera according to the size of the pinhole. Each disk of light  casts  onto the back overlaps and blurs with disks from nearby atoms.

One can reduce the blur by making the pinhole smaller. However, then the image becomes darker and may not be visible or recordable on film.

Extended Learning – Activities and Projects

1. Phenomenon of path travelled by light and reflection of light from mirror.
Fix a comb on one side of a large thermocol sheet and fix a mirror on the other side as shown in the figure. Spread a dark-coloured sheet of paper between the mirror and the comb. Keep this in sunlight or send a beam of light from a torch through the comb. What do you observe? Do you get a pattern similar to that shown in the figure?

Light travels in straight line and gets reflected from the mirror. Yes, we get a pattern similar to that shown in the figure.

2.  To observe the path of light.

•     Take a chart paper and roll it into a pipe. Look at a lighted candle through it as shown in. Take care not to touch the chart paper with the flame.
•     Now bend the pipe from the middle and repeat the activity as shown in. Why are you not able to see the lighted candle through the bent pipe?

Light travels in a straight line and does not bend with the pipe.