How a camera works Lens CCD Photosite VCR Sensor Zoom Aperture Shutter Light
The Basics • A camera section, consisting of a CCD, lens and motors to handle the zoom, focus and aperture • A VCR section, in which a typical TV VCR is shrunk down to fit in a much smaller space. • The camera receives visual information; • The VCR records the information.
Aperture • The opening in the lens that controls the given amount of light that enters the camera. • The smaller the opening, the higher the number. • The camcorder monitors the photosite charges and adjusts the camera's iris to let more or less light through the lenses.
Aperture • The aperture is the size of the opening in the camera. It's located behind the lens. On a bright sunny day, the light reflected off your image may be very intense, and it doesn't take very much of it to create a good picture. In this situation, you want a small aperture. But on a cloudy day, or in twilight, the light is not so intense and the camera will need more light to create an image. In order to allow more light, the aperture must be enlarged.
Shutter Speed • Traditionally, the shutter speed is the amount of time that light is allowed to pass through the aperture. • Think of a mechanical shutter as a window shade. It is placed across the back of the aperture to block out the light. Then, for a fixed amount of time, it opens and closes. The amount of time it is open is the shutter speed. One way of getting more light into the camera is to decrease the shutter speed -- in other words, leave the shutter open for a longer period of time.
Video vs. Film • Once film is exposed, it cannot be used again. Its chemicals react to light to form a latent image. • The sensor in a digital camera can be reset electronically and used over and over again. This is called a digital shutter. Some digital cameras employ a combination of electrical and mechanical shutters.
Point and Shoot • Exposing the SensorThese two aspects of a camera, aperture and shutter speed, work together to capture the proper amount of light needed to make a good image. In photographic terms, they set the exposure of the sensor. Most digital cameras automatically set aperture and shutter speed for optimal exposure, which gives them the appeal of a point-and-shoot camera.
Some digital cameras also offer the ability to adjust the aperture settings by using menu options on the LCD panel. More advanced hobbyists and professionals like to have control over the aperture and shutter speed selections because it gives them more creative control over the final image. As you climb into the upper levels of consumer cameras and the realm of professional cameras, you will be rewarded with controls that have the look, feel and functions common to film-based cameras.
Lens • In any sort of camera, you can magnify a scene by increasing the focal length of the lens. • An optical zoom lens is a single lens unit that lets you change this focal length. • A zoom range tells you the maximum and minimum magnification.
Focal Length • The important difference between the lens of a digital camera and the lens of a 35mm camera is the focal length. The focal length is the distance between the lens and the surface of the sensor. The surface of a film sensor is much larger than the surface of a CCD sensor. In fact, a typical 1.3-megapixel digital sensor is approximately one-sixth of the linear dimensions of film. In order to project the image onto a smaller sensor, it is necessary to shorten the focal length by the same proportion.
The CCD • Like a film camera, a camcorder "sees" the world through lenses. • . The lens in a camcorder serves to focus light; it shines the light onto a small semiconductor image sensor. • This sensor, a charge-coupled device (CCD), measures light with a half-inch (about 1 cm) panel of 300,000 to 500,000 tiny light-sensitive diodes called photosites.
Just as an artist sketches a scene by contrasting dark areas with light areas, a CCD creates a video picture by recording light intensity. • To create a color image, a camcorder has to detect not only the total light levels, but also the levels of each color of light. Since you can produce the full spectrum of colors by combining the three colors • red, green and blue, a camcorder actually only needs to measure the levels of these three colors to be able to reproduce a full-color picture.
Capturing Color • Unfortunately, each photosite is colorblind. It only keeps track of the total intensity of the light that strikes its surface. In order to get a full color image, most sensors use filtering to look at the light in its three primary colors. Once all three colors have been recorded, they can be added together to create the full spectrum of colors
Color • Capturing Color: Beam Splitter • Capturing Color: Spinning DiskCapturing Color: Interpolation • Digitizing Information
The Lens • When the camera is zoomed in, it is difficult to maintain focus, especially when there is movement from either the camera or subject. • This is why all camcorders come with an autofocus device, usually an infrared beam that bounces off objects in the center of the frame and comes back to a sensor on the camcorder. • To find the distance to the object, the processor calculates how long it takes the beam to bounce and return, multiplies this time by the speed of light, and divides the product by two
digital zoom. This doesn't involve the camera's lenses at all; it simply zooms in on part of the total picture captured by the CCD, magnifying the pixels. • Since it magnifies the scene, however, the resolution is not as good as an optical zoom.