The lens focuses light as it passes through to the film plane or digital sensor.
Light passes through multiple camera controls to create an image on film or a digital sensor. These controls vary depending on the type of camera you are using; however, every camera has a lens, a shutter and an aperture, regardless of whether you have manual control over them. Once the camera focuses and controls the amount of light for a given situation, film turns dark according to the amount of light present, or a digital sensor converts the light into data.
Lens
A camera lens usually consists of six or eight separate lenses called elements. Each element has at least one curved side, if not two, to compensate for focusing defects in the others. These convex lenses refract the light so rays of light that bounce off an object are focused at a single point on the film plane or sensor. A lens with a short focal length, such as 28 mm, bends rays of light more than one of a longer focal length because of the shorter distance between the lens elements and film plane. The result is an image with a wider angle of view when you use a short focal length lens and an image of greater magnification with a long lens.
Aperture Ring
The aperture is a diaphragm present in the lens of a camera that controls the width of the opening, allowing light to pass onto the film plane or sensor. The wider this opening, the more of a difference you'll see in the focus between the background and foreground. This is referred to as a photograph's "depth of field." When the aperture opening is wide, light passes through different thicknesses of the convex lens, creating variations in sharpness of the image, depending on depth. When the aperture opening is small, light passes through a more uniform area of thickness on the lens, resulting in a wider depth of field with more sharpness throughout the image.
SLR Pentaprism
If you have a single-lens reflex or SLR camera, it contains a series of mirrors called a pentaprism. The pentaprism is what allows you to see in the viewfinder exactly what your lens sees. Light reaches a mirror bent at a 45-degree angle in the camera body, which bounces the light up into the pentaprism. It then turns at a series of angles allowing you to see an image in the viewfinder. When you press the shutter release button, this first mirror drops down so that light can hit the film or sensor and you momentarily cannot see the image in the viewfinder because the light is striking the film or sensor.
Shutter
SLR cameras use a focal plane shutter that is built into the camera body. This type of shutter has two overlapping curtains that create slits allowing light to pass through to the film or sensor. Large-format cameras, some medium-format cameras and point-and-shoot cameras use a leaf shutter. A leaf shutter has multiple overlapping blades that retract, creating a circular opening from the center to let light pass through.
Capture
After these controls, light finally reaches the film plane or digital sensor. Wherever light strikes the film, the light-sensitive silver compound on the film surface turns dark. When reversed in an enlarger, these dark areas correspond to highlights in an image. The longer light passes through, the darker the film becomes. A digital camera's sensor is made of millions of photosites, resembling a checkerboard. The photosites collect electrons as light strikes them and store this information as numerical data. Computers interpret these numbers and create a photographic image with the information.
Tags: film plane, passes through, digital sensor, light passes through, film sensor
