Digital single-lens reflex camera

Digital single-lens reflex cameras (Digital SLRs or DSLRs) operate on the same principle as standard film single-lens reflex cameras. The key difference is that the film is replaced with an electronic sensor (such as a CCD or CMOS sensor), giving the advantage of needing no film and other features common to digital cameras. Like SLRs, DSLRs are often used by professional photographers and advanced amateurs.

The purpose of the digital SLR is to allow experienced photographers to use the tools and techniques that they are familiar with from film SLRs while gaining the advantages of a digital camera. For this reason, camera manufacturers design digital SLRs to be as similar as possible to their film counterparts. A single-lens (no separate viewfinder) means that the photographer can focus through the lens itself and see the shot without parallax effects. Cameras which have a separate viewport (such as most point-and-shoot cameras) can produce a photograph which is framed differently from the photographer's intent. Another advantage of the digital SLR is the ability to accept the standard lenses used with film SLR cameras. Canon produces over 50 different interchangeable lenses for their EOS cameras. Sigma, Tamron, and Tokina each manufacture lenses to fit a variety of camera mounts inluding the Canon and Nikon. Note, however, that the electronic sensor is often smaller than a conventional 35 mm film frame, so results are slightly different from what might be expected; effectively, it is as if the 35 mm frame is first enlarged and then cropped.

DSLR accepts interchangeable lenses and accessories such as flash units, and accessories for SLRs are usually compatible with DSLRs of the same brand. When aiming a DSLR, the photographer is looking through the lens (unlike a rangefinder camera or a camera with a separate viewfinder) and the image is projected optically (unlike a camera with an electronic viewfinder).

The imaging sensor in a DSLR is typically much larger than the one in a standard digital camera. Larger sensor allows better image quality, shallower depth of field and wider field of view. However, the sensor is usually smaller than a frame of 135 film. The average size of a typical DSLR sensor being about 22 mm x 15 mm, or the size of an APS film frame. If this is not the case and the sensor is the same size as the equivalent frame of film (usually 35 mm wide), the camera is said to have a full-frame sensor. Currently (2005) only some expensive professional DSLRs have full-frame sensors (typically 36 mm x 24 mm). One example of a full-frame DSLR is the Canon EOS-1Ds Mark II.

Depending on the position of the reflex mirror, the light from the scene can only reach either the eyepiece or the sensor. Also, a mechanical shutter is used to control the exposure. Therefore even though a DSLR has a color display at the back of the camera body, it doesn't provide "live preview" (allowing focusing and framing using the display). The only exception to this rule so far is Canon EOS 20Da, a Japanese variant of Canon EOS 20D designed for astrophotography.

Camera manufacturers expect that professionals and advanced amateurs continue to prefer DSLRs over other forms of digitals cameras. However, if electronic viewfinders with near-zero lag and very low energy consumption are introduced, non-SLR cameras may become a viable choice for a large number of people who now need SLRs.

Many medium format SLRs can accept a digital camera back to turn the camera into a kind of DSLR with very high image quality (typically 22 megapixel as of 2005). However, the combination is very expensive and bulky, and thus they are rarely used outside fashion photography and portraiture.

History

At Fotokina, 1986, Nikon revealed a protoype anolog electronic still SLR camera, the Nikon SVC, a precurser to the digital SLR (Pierre J., "Nikon SLR-type digital Cameras", [1]). The prototype design lead to the Nikon N8008 two years later capable of 0.3 megapixel (ibid [2]).

In 1991, Kodak released the first comercially available digital SLR, the Kodak DCS-100. It consisted of a modified Nikon F3 SLR body, modified drive unit, and an external storage unit connected via cable. The camera was capable of producing 1.3 megapixel (1280x1024) and cost approximately $30,000 US. This was followed by the DCS-200 with integrated storage (Leefoo, "A Brief Info on Kodak DCS-Series Digital Still SLR cameras", [3]).

Over the next decade, digital SLRs have been released by various companies (prominant names include Canon, Nikon and Kodak) with higher resolution (megapixel) and lower prices.

In 2003, Canon introduced a 6.3 megapixel Digital Rebel SLR camera (known in the UK as the EOS 300D) at an MSRP of under $1000. Its popularity, especially among newspaper and amateur photographers, encouraged other manufacturers to produce affordable digital SLR cameras, significantly lowering entry costs and allowing more casual photographers an opportunity to experience Digital SLR. Canon introduced the next generation 8 megapixel EOS350D (Digital Rebel XT) in 2005.

As of 2005, only Canon currently carries a "Full Frame" dSLR- that is a dSLR with a sensor with the same dimensions as 35mm film, the 16 megapixel EOS 1Ds mkII. Such a camera does not suffer from the "magnification factor". Kodak previously released two Full Frame cameras for Nikon and Canon lens mounts, but have discontinued them, due to the very high current cost of making "Full Frame" DSLR's. However, Canon have just launched the new EOS 5D (October 2005) and it will retail for around half the price of the 1Ds mkII, making "Full Frame" DSLR's more affordable to the public and proffessionals alike. With a 12 megapixel CMOS sensor and a very high spec, this could be the start of a slow but steady "Full Frame" DLSR influx which will gather momemtum as time moves on and prices come down, and will pose a problem for people that have bought a current DSLR with lenses designed to work only with the smaller Sensor.

Nikon has a broad line of SLRs which, in 2005, includes the D2X and D2H as well as the Canon 300D competitor, the D70. Kodak and Fujifilm sell models based on Nikon lens mount, and Kodak also sells one that accepts Canon lenses. Olympus has introduced two digital SLRs. Pentax and Konica Minolta also have digital SLRs that use their lenses and accessories.

Konica Minolta incorporates technology for reducing the effects of camera shake (Canon and Nikon put similar capabilities in certain of their lenses). Kyocera manufactured SLRs and marketed them under the Contax name, but in 2005 withdrew from the digital-camera field.

Digital SLR versus Digital compacts(Digital Non-SLRs)

What is the edge of Digital SLRs over non-SLR digital cameras?

Non-SLR digitals are of 2 types, digital compacts and SLR-like "prosumer"compacts (e.g., Minolta DimageZ2, Nikon 5700). Prosumer digitals have lenses with large zoom capacity (10x-12x) which even vies with some DSLRs.

In the conventional film photography, the SLR method's biggest advantage over Rangefinder method is TTL (Through The Lens) viewing of the image to be photographed. In a Rangefinder camera, the frame is seen via a prism, not through the focusing lens and this accounts for the parallax error - ie. the frame seen in viewfinder is not exactly the frame which will impinge on the film plate.

However, most non-SLR Prosumer digitals (like Nikon 5700) also offer TTL viewing through the focusing lens, projected onto its viewfinder as well as the LCD screen,through an EVF(electronic viewfinder). This differs from the DSLR in that this is a digitally created image whereas a DSLR gives the real optical TTL image. An EVF image is slower to readjust(lag) to a change and of lower resolution than a true optical TTL. Advantages of EVF are parallax free views and far lesser bulk than a DSLR.

A DSLR camera shows the true optical image in its viewfinder.Since the mirror sits in front of the sensor(reflecting the image to the viewfinder)the LCD screen of a DSLR shows the snap only after being shot, but not before clicking. DSLRs allows for easy lens interchanges, which is not available in all but one non-SLR digital cameras (Epson R-D1 Rangefinder [4]). (High end rangefinder cameras of conventional film photography allows lens interchange.) DSLR is also faster (time from the clicking to sensor and then to store the snap onto the memory card) than digital compacts ,which helps in action photography.SLR also gives more control on aperture and shutter speed, which matters for artistic photography.

Thus, generally,DSLRs combine the plus points of both conventional and digital photography. But the gap between the digital SLR and Non-SLR is closing in as most digital Non-SLRs have overcome the inherent problems of the Rangefinders of conventional photography, notably the parallax-error.They are far cheaper and smaller than a DSLR and provide phenomenal zooms,which all appeal to amateurs.

The main drawbacks of DSLR are the cost and bulk of the equipment(as it houses the flipping pivoted reflecting mirror between the lens and the sensor)

DSLR also suffers dust over the sensor problem.Because of the interchangeabilty of lenses, environmental dust accumulates on the super-thin glass cover in front of the sensor.It has to be cleaned periodically to avoid surprising blotches in the enlarged print outs.If not properly done,permanent scratches will be etched on the glass cover and spoils the performance.

See also

• digital photography