A digital camera is a camera that captures photos in digital memory. Most cameras manufactured today are digital and have largely replaced those that capture images on photographic film. Digital cameras are now widely integrated into mobile devices such as smartphones, with the same or more capabilities and features as dedicated cameras (which are still available). High-end specialized high-resolution cameras are still commonly used by professionals and those who want to take higher quality photos.
Digital and digital film cameras share an optical system, usually using a variable aperture lens to focus light onto the imaging device. The diaphragm and shutter let a controlled amount of light into the image, just as with film, but the image capture device is electronic rather than chemical. However, unlike film cameras, digital cameras can display images on the screen immediately after recording and store and delete images from memory. Some digital cameras can crop and stitch images and perform other basic image editing.
The two main types of digital image sensors are CCD and CMOS. A CCD sensor has one amplifier for all pixels, while each pixel in a CMOS active pixel sensor has its own amplifier. Compared to CCD, CMOS sensors consume less power. Small-sensor cameras use a back-illuminated CMOS (BSI-CMOS) sensor. A camera’s image processing capabilities determine the outcome of the resulting image quality much more than the sensor type.
The resolution of a digital camera is often limited by the image sensor, which converts light into discrete signals. Depending on the physical structure of the sensor, an array of color filters may be used which requires demosaicing to recreate a full color image. The number of pixels in the sensor determines the “pixel count” of the camera. In a typical sensor, the number of pixels is the product of the number of rows and the number of columns. For example, a 1000 x 1000 pixel sensor would have 1,000,000 pixels or 1 megapixel.
A firmware resolution selector allows the user to optionally lower resolution, reduce file size per image, and extend lossless digital zoom. The lower resolution is usually 640 × 480 pixels (0.3 megapixels).
A lower resolution extends the number of photos left in free space, thus delaying storage depletion, which is useful where no additional storage device is available and for less important images where the benefit of lower storage consumption outweighs the disadvantage of reduced detail.
The digital camera lens captures the light from the object and focuses it onto the sensor. The design and manufacture of the lens are decisive for the quality of the photographs. A technological revolution in camera design during the 19th century modernized optical glass production and lens design. This contributed to modern manufacturing processes for a wide variety of optical instruments such as reading glasses and microscopes. Pioneering companies include Zeiss and Leitz.
Camera lenses are manufactured in a wide range of focal lengths such as ultra-wide, standard and medium telephoto. Lenses have either a fixed focal length or a variable focal length (zoom lens). Each lens is best suited for certain types of photography. Extremely wide angles may be preferred for architecture due to their ability to capture a wide view of buildings. Standard lenses normally have a wide aperture and are therefore often used for street and documentary photography. A telephoto lens is useful for sports and wildlife, but is more prone to camera shake, which can cause motion blur.
An image of flowers, with one in focus. The background is out of focus od digital camera.
The range of distance at which objects appear bright and sharp, called depth of field, can be adjusted with many cameras. This allows the photographer to control which subjects appear in focus and which do not.
Due to the optical properties of the photographic lens, only objects within a limited range of distance from the camera will be clearly reproduced. The process of adjusting this range is known as changing the camera’s focus. There are different ways to accurately focus your camera. The simplest cameras have fixed focus and use a small aperture and wide-angle lens to ensure that everything within a certain range of distance from the lens, usually around 3 meters (10 ft) to infinity, is reasonably in focus. Fixed focus cameras are usually inexpensive, such as disposable cameras. A camera may also have a limited focus range or focus according to a scale marked on the camera body. The user estimates or calculates the distance to the subject and adjusts the focus accordingly.
A flash provides a short burst of bright light during exposure and is a commonly used artificial light source in photography. Most modern flash systems use a battery-powered high-voltage discharge through a gas-filled tube to generate bright light for a very short time (1/1,000 of a second or less).
Many flash units measure the light reflected from the flash to help determine the appropriate duration of the flash. When the flash is attached directly to the camera—typically in a slot at the top of the camera (the flash shoe or hot shoe) or through a cable—activating the shutter on the camera triggers the flash, and the camera’s internal light meter can help determine the duration of the flash.
After exposure, each photo is captured using pressure rollers inside the instant camera. The developing paste contained in the paper “sandwich” is thus spread over the image. After a minute, just remove the cover sheet and one will have a single original positive image with a fixed format. With some systems, it was also possible to create an instant image negative, from which copies could then be made in a photo lab. The final development was Polaroid’s SX-70 system, in which a series of ten pictures could be taken – powered by a motor – without having to remove the cover sheets from the image. There were instant cameras for various formats, as well as adapters for instant film use in medium and large format cameras.
Subminiature cameras were first made in the nineteenth century and use film significantly smaller than 35mm. The expensive 8×11mm Minox, the only type of camera produced by the company between 1937 and 1976, became very famous and was often used for espionage (Minox later produced larger cameras). Later inexpensive subminiatures were produced for general use, some using reshot 16mm motion picture. Image quality was limited at these small film sizes.
The introduction of films allowed existing plate camera designs to be much smaller and the base plate to be foldable so that the bellows could be folded and compressed. These designs were very compact and the small models were called pocket cameras. Folding film cameras were preceded by folding-plate cameras, more compact than other designs.
Box cameras were introduced as cheap cameras and had few if any controls. The original Brownie box models had a small mirrored viewfinder mounted on the top of the camera and had no aperture or focus controls and only a simple shutter. Later models such as the Brownie 127 had larger direct-view optical viewfinders along with a curved film path to reduce the impact of lens imperfections.