The Pinhole Camera

A pinhole camera is a simple version of a camera, which does not have a lens. It is a light proof box with a small hole (the size of a pin tip) on one side and a screen on the other side. A pinhole camera works in a similar way to the eye.

A detailed illustration of a tree with a lush green canopy and sturdy brown trunk on the left. On the right, there's a rectangle framing an upside-down section of the tree's top, highlighting the inverted reflection or perspective of the tree's canopy and part of its trunk. Diagonal lines connect the corresponding parts of the tree to its inverted section inside the rectangle.

In the diagram above, you can see that the light rays hit the screen at the back, and then the image is projected onto the screen. As the image can be projected onto the screen, it is called a real image. This projected image is different from a mirror image, which we call a virtual image.

Like the eye, the image formed on the screen is upside down. However, the retina in our eyes sends this information to the brain, which then turns the image the right way up so we can see it correctly. In a simple pinhole camera, the image formed will be upside down.

diagram illustrating the behaviour of light when passing through a convex lens. Parallel rays of light, coming from the left and represented by lines of various colours, converge after passing through the lens. These rays meet at a focal point on the right side of the lens. The distance between the lens and the focal point is labelled as 'Focal length'. The vertical line passing through the centre of the lens is marked as 'Optical Axis', while the horizontal line is labelled 'Principal Axis'. An 'Optical Center' is also indicated on the lens.

There are many similarities between the pinhole camera and the eye. The pinhole acts like the pupil, the hole at the centre of the iris that lets light through, forming an upside-down image. However, an eye has a much more complex structure.

The convex lens is right behind the pupil. It can get thinner or thicker, allowing us to see both far-away and up-close objects. Also, the convex lens bulges out on both sides, helping to focus light on the retina, which is the focal point.

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