A digital camera is an electronic device used to capture and store photographs electronically instead of using photographic film like conventional cameras. Modern compact digital cameras are typically multifunctional, with some devices capable of recording sound and/or video as well as photographs. In the Western market, digital cameras now outsell their 35 mm film counterparts.
Digital cameras can be classified into several groups:
Video cameras
Professional video cameras such as those used in television and movie production. These typically have multiple image sensors (one per color) to enhance resolution and color gamut. Professional video cameras usually do not have a built-in VCR or microphone.Camcorders used by amateurs. They generally include a microphone to record sound, and feature a small LCD to watch the video during taping and playback.Webcams are digital cameras attached to computers, used for video conferencing or other purposes. Webcams can capture full-motion video as well, and some models include microphones or zoom ability.In addition, many still digital cameras have a "movie" mode, in which images are continuously acquired at a frame rate sufficient for video.
Still cameras
Canon PowerShot A95 with CompactFlash card loaded
Digital still cameras are cameras whose primary purpose is to capture photography in a digital format. Initially, a digital camera was characterized by the use of flash memory and USB or FireWire for storage and transfer of still photographs (though some early cameras used a serial port connection), and this is still the common meaning of the unadorned term. Many modern digital photography cameras have a video function, and a growing number of camcorders have a still photography function. However, even a low-end still camera can take far better still pictures than a mid-range video camera, and mid-range still cameras have much lower video quality than low-end video cameras. In addition, some newer camcorders record video directly to flash memory and transfer over USB and FireWire. Among digital still cameras, most have a rear LCD for reviewing photographs. They are rated in megapixels; that is, the product of their maximum resolution dimensions in millions. The actual transfers to a host computer are commonly carried out using the USB mass storage device class (so that the camera appears as a drive) or using the Picture Transfer Protocol and its derivatives, in addition firewire is becoming more popular and supported among more digital cameras. All use either a charge-coupled device (CCD) or a complementary metal-oxide semiconductor (CMOS) sensor or novel sensors based upon either of those two principles, i.e. chips comprised of a grid of phototransistors to sense the light intensities across the plane of focus of the camera lens. CMOS sensors are differentiated from CCDs proper in that it uses less power and a different kind of light sensing material, however the differences are highly technical and many manufacturers still consider the CMOS chip a charged coupled device. For our purposes, a chip sensor is a CCD.
Canon PowerShot A60
Compact digital cameras
Also called digicams, this encompasses most digital cameras. They are characterized by great ease in operation and easy focusing; this design allows for limited motion picture capability. They tend to have significantly smaller zooms than prosumer and DSLR cameras. They have an extended depth of field. This allows objects at a larger range of depths to be in focus, which accounts for much of their ease of use. It is also part of the reason professional photographers find their images flat or artificial-looking. They excel in landscape photography and casual use. They typically save pictures in only the JPEG file format.
Prosumer cameras
Fujifilm FinePix S9000
Bridge digital camera
Prosumer cameras or extended zoom cameras form a general group of higher end cameras that physically resemble SLR "professional" cameras and share some features, but are still geared towards consumers. Thus, the name prosumer from professional and consumer. These cameras tend to have a large optical zoom lens, which compromises a "do it all" ability with barrel distortion and pincushioning. Prosumer cameras are sometimes marketed as and confused with digital SLR cameras since the bodies resemble each other. The distinguishing characteristics are that prosumer cameras do not have a removable lens (although accessory wide angle or telephoto lenses can be attached to the front of the main lens), can usually take movies, record audio and the scene composition is done with either the LCD display or the electronic viewfinder (EVF). The overall performance tends to be slower than a true digital SLR, but they are capable of very good image quality while being more compact and lighter than DSLRs. The high-end models of this type have comparable resolutions to low and mid-range DSLRs Many of the these cameras can save in JPEG or .RAW format.
Digital single-lens reflex camera
Nikon D50
Digital single-lens reflex camera
DSLRs are conceived for professional photographers and are well adapted for action photography or specialized uses. They are based on film single-lens reflex cameras and retain their main features : image composing done through the optical viewfinder using a mirror reflected image and exchangeable lenses, albeit a few early SLR digital cameras like the Olympus E-10 have a fixed lens.
The ability to change lenses gives the same benefits as in film cameras, allowing tailoring a lens to an intended use instead of a compromise. They can use the same lenses as their film counterparts, but the sensor is usually smaller than that of 35 mm film. A common term is "APS class," being the same general size as APS film. Focusing on the smaller area results in digital cameras having a zoom of 1.5 to 2.0 times over the same lens on a 35 mm film camera. Thus a 50 mm lens on a DLSR with a 1.5 crop ratio would show the same angle of view as a 75 mm lens on a 35 mm camera.
DSLR cameras have larger image sensors than compacts or prosumers, and thus higher sensitivity in dim lighting and less noise overall in the pictures they take. They usually are instantly on and the autofocus and operation is faster. Most of them can save in JPEG and raw formats even simultaneously.
They are bulkier, heavier and frequently much more expensive. Two characteristics many consumers are surprised to find due to the reflex viewfinder is they cannot record movies and the screen is only for reviewing pictures. All composing is done through the optical viewfinder, has more resolution than an electronic viewfinder and does not produce any delay. In 2006 the Olympus E-330 is the only DSLR that can use the LCD for a live preview, and will be joined by the Panasonic Lumix DMC-L1.
Professional modular digital camera systems
When digital cameras became common, a question many photographers asked was if their film cameras could be converted to digital. The answer was yes and no. For the majority of 35 mm film cameras the answer is no, the reworking and cost would be too great, especially as lenses have been evolving as well as cameras. For the most part a conversion to digital, to give enough space for the electronics and allow an LCD screen to preview, would require removing the back of the camera and replacing it with a custom built digital unit.
Many early professional SLR cameras, such as the NC2000 and the Kodak DCS series, were developed from 35 mm film cameras. The technology of the time, however, meant that rather than being a digital "back" the body was mounted on a large and blocky digital unit, often bigger than the camera portion itself. These were factory built cameras, however, not aftermarket conversions.
A notable exception was a device called the EFS-1, which was developed by Silicon Film from ca. 1998-2001. It was intended to insert into a film camera in the place of film, giving the camera a 1.3 MP resolution and a capacity of 24 shots. Units were demonstrated, and in 2002 the company was developing the EFS-10, a 10 MP device that was more a true digital back.
A few 35 mm cameras have had digital backs made by their manufacturer, Leica being a notable example. Medium format and large format cameras (those using film stock greater than 35 mm), have users who are capable of and willing to pay the price a low unit production digital back requires, typically over $10,000. These cameras also tend to be highly modular, with handgrips, film backs, winders, and lenses available separately to fit various needs.
The very large sensor these backs use lead to enormous image sizes. The largest in early 2006 is the Hasselblad H2D, which makes images 39 MP in size from a 36.7 mm × 49 mm sensor. Medium format digitals are geared more towards studio and portrait photography than their smaller DSLR counterparts, the ISO sensivity in particular tends to have a maximum of 400, versus 3200 for some DSLR cameras.
Since the first backs were introduced there have been three main methods of "capturing" the image, each based on the hardware configuration of the particular back.
The first method is often called "Single Shot," in reference to the number of times the camera's sensor is exposed to the light passing through the camera lens. Single Shot capture systems use either one CCD with a Bayer filter stamped onto it or three separate CCDs (one each for the primary additive colors red, green and blue) which are exposed to the same image via a beam splitter.
The second method is referred to as "Multi-Shot" because the sensor is exposed to the image in a sequence of three or more openings of the lens aperture. There are several methods of application of the multi-shot technique. The most common originally was to use a single CCD with three filters (once again red, green and blue) passed in front of the sensor in sequence to obtain the additive color information. Another multiple shot method utilized a single CCD with a Bayer filter but actually moved the physical location of the sensor chip on the focus plane of the lens to "stitch" together a higher resolution image than the CCD would allow otherwise. A third version combined the two methods without stamping a Bayer filter onto the chip.
The third method is called "scan" because the sensor moves across the focus plane much like the sensor of a desktop scanner. These CCDs are usually referred to as "sticks" rather than "chips" because they utilize only a single row of pixels (more properly "photosites") which are again "stamped" with the Bayer filter.
The fourth method is a rotational scan of a linear sensor. A digital rotating line camera offers images of very high resolution.
The choice of method for a given capture is of course determined largely by the subject matter. It is usually inappropriate to attempt to capture a subject which moves (like people or objects in motion) with anything but a single shot system. However, the higher color fidelity and larger file sizes and resolutions available with multi-shot and scan-backs make them attractive for commercial photographers working with stationary subjects and large-format photographs.