How Do SLR Camera Lenses Work?
The Purpose of an SLR Camera
SLR stands for single-lens reflex. Its purpose is to provide a photographer with an exact view of what will appear in the frame of a particular picture to be taken. This means that the photographer will not accidentally cut anything out of her photograph.
How SLR Lenses Show the Image to be Taken
SLR lenses project the image a photographer is about to take into either the eyepiece or the shutter and to the film, but never to both concurrently. This is done with a mirror, a series of lenses, and a pentaprism. When a photographer looks through the eyepiece, the light reaching his eye has been sent through the SLR lens, but not to the shutter. The incoming light goes through all the lenses that are in front of the shutter (also known as the lens assembly). However, instead of hitting the shutter, the light is reflected upward by a mirror that rests at a 45-degree angle to the light's original path. This reflects the light 90 degrees upward and into a focusing screen and through a condensing lens. This lens directs the light through to a pentaprism, which is a prism that has five sides. The light is reflected off the inside walls of the prism until it goes directly to the eyepiece. The pentaprism is used to ensure that the image displays without being flipped.
How SLR Camera Lenses Take a Picture
It may seem that a 45-degree mirror in front of the shutter would inhibit light from reaching the shutter to take a picture. However, when a picture is taken, the mirror turns to a horizontal position as the shutter opens. This allows light to go through the shutter and onto the film, where it is captured as a picture. Because the mirror is flipped up, the eyepiece goes dark momentarily as the picture is taken.
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