Aperture An adjustable iris or opening through which light enters a camera's lens. The larger the aperture is, the greater the camera's photosensitivity. A smaller aperture, however, gives greater depth of field to a picture. The aperture setting is called the f-stop. A small aperture has a relatively high f-number, such as f8 or f11, and a larger aperture has a smaller number, such as f2.8. The aperture setting must be balanced against the shutter speed. The faster the shutter speed, the larger the aperture must be, and vice versa, to admit the right amount of light to the image sensor for proper exposure.
Compression A process that reduces the amount of data representing an image so that the file takes up less space in your camera, memory card, and computer. Compressing and saving an image actually takes less time than saving an uncompressed image. Smaller files are quicker to use for e-mail and on the Web. When a file is overcompressed, however, image quality can be seriously degraded.
Depth of field An indication of how much of a scene will be sharp and in focus. A greater depth of field implies an increased distance between well-focused background and foreground, with everything in between properly focused. A narrow depth of field concentrates its area of focus within a small range, based on the central subject's distance from the camera. For instance, if your subject is standing alone in a ballpark, using a narrow depth of field will make most of the ballpark look blurry; only the subject will be focused. A greater depth of field might keep most of the ballpark in focus.
Image sensor The semiconductor chip in a digital camera that replaces film. It captures the light of a scene or subject, which it turns into electrical signals that the camera can understand and use. The camera in turn converts these signals to digital data that your computer can understand and use. The most common image sensor types are CCD (charge-coupled device) and CMOS (complementary metal-oxide semiconductor).
Interpolation A process that increases the image file size and can occur either in your camera or by computer software. Interpolation allows a picture to be magnified but does not improve image quality and can decrease sharpness. It is the opposite of compression.
LCD viewfinder A small electronic screen on the back of a digital camera that displays what the lens sees. You would use it to compose your picture, choose your settings, focus and frame an image in macro mode, and view just-shot photos.
Megapixel A measure of a digital camera's resolution. A one-megapixel rating means that the camera can capture up to 1 million pixels, or points of data.
Memory card A small, removable storage device that saves the images a digital camera captures. When it is full, you can swap one memory card for another and continue shooting. A card reader can be attached to your computer for opening and saving image files outside of your camera. Memory cards come in various densities, as do any other drives or storage devices. The most common types of memory cards are CompactFlash, SmartMedia, and Secure Data (SD), with Sony's Memory Stick a distant fourth. You must use the right type of card for your digital camera.
Pixel A point of data in a digital image; the word is short for picture element. A digital camera's resolution is a measure of the number of pixels it can capture on its image sensor.
Shutter speed A measure of how long a camera allows light to fall on the active image sensor (expressed as a fraction of a second). In traditional film cameras, there is a physical, mechanical shutter in the lens that opens and closes to regulate how long the film is exposed to light. Though many digital cameras have both electronic and mechanical shutters, inexpensive models rely solely on electronic shutters that turn off the photosensitivity of the image sensors.
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