How does pinhole camera work?
Every point on the surface of a visible object emits or reflects light rays in all directions.
In order for vision to work, the lens inside the eye serves to bring the light rays to a common focus. The everyday camera works in a similar way to the eye. The pinhole camera does not have a lens for focusing.
How does the pinhole work without using a lens?
Light rays travel in a straight path. In theory, if the pinhole is tiny enough, it will only allow one ray of light from any point of an object to pass through it. It will then intersect with the with film pane at one point. The accumulation of these single light rays from every point of the object will form the image of the object on film pane. This is how a pinhole camera “focuses” its image. However, since the pinhole is not a “point” but a hole, instead of a single light ray, it allows a small bundle of light rays to pass through. Thus images formed in pinhole cameras are a bit softer than from everyday cameras with have a focusing lens. A smaller pinhole will produce sharper images. However, the image will be dimmer too as the number of light rays allowed to pass through the hole is less, so exposure times will be longer to achieve the proper exposure of image.