The lens is by far the most important element in a camera. Its function is to collect and bend light rays onto the sensor (film) so that you will get a sharp, correctly coloured image of whatever you photograph.
If you’ve ever looked through an ordinary magnifying glass, you’ve probably noticed that colours viewed through the lens tend to separate, giving the magnified objects rainbow-like edges.
The same thing happens in a camera lens. By bending and redirecting the light, the many glass elements in the lens, which are precisely assembled at specified distances and orientations, correct both the distortions in shape and the aberrations in colours.
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In addition, the metal tube that holds the collection of glass elements is itself a complexly engineered product, with controls that allow you to adjust the amount of light passing through the lens and to focus.
The control that enables you to adjust the amount of light reaching the film(sensor)is the aperture ring. Its location varies from camera to camera.
Whatever its position, the aperture ring controls an adjustable diaphragm – a series of overlapping metal blades that together operate much like the iris of the eye.
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The size of the opening created as the blades open and close determines the amount of light passing through.
The diaphragm can be opened to let in all the light the lens collects or it can be closed down to let only a tiny dot of light through. And, of course, it can be adjusted for any amount of light in between.
The size of this opening, or aperture, is usually indicated in f-numbers 1.4, 2, 2.8, 4, 5.6, 8, 11, 16, 22 and 32. The larger the number, the smaller the opening. On most lenses for 35mm cameras, the smallest aperture is f/16, f/22.
The largest aperture varies, but on most models, it is at least f/2.8. On more expensive models, it is often f/2 or even wider.
F – numbers are arrived at by a formula based on the ratio of the size of the opening to the lens’s focal length. The lens on most compact rangefinder has a focal length between 35mm and 45mm.
Normal lenses have a focal length between 50mm and 55mm. Lenses with a focal length longer than 55mm are telephoto lenses.
Both the focal length and the maximum aperture of a lens are engraved on the ring around the front of the lens.
I started the road of photography, repairing some film cameras. But soon I've realised that I need some knowledge on how the photos are formed inside the camera. This road is tougher than I thought, but life is always a learning experience, and I am hoping that you could join me in this wonderful world of photography.
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