Cameras work a lot like the human eye. In a modern camera (as in your smart phone) a convex lens focuses the image on an electronic sensor. The distance between the lens and the sensor determines the size of the image – a longer focal length results in a magnified view. The trade-off with increasing the focal length and image size is that the amount of area visible (the field of view) decreases. On larger cameras the diameter of the lens opening can be changed (similar to the iris of the human eye) to let in more light or to restrict the amount to ensure a correctly illuminated image. On most smart phone cameras the amount of light is controlled by varying the amount of time that light passes through the lens.


Electronic sensors in cameras contain millions of light-sensitive elements called pixels on an imaging chip. The sensor information is converted to ones and zeros that camera software converts into pictures that are instantly displayed on the camera screen. Selfies result from basic principles of physics being cleverly squeezed into a small phone.


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