What is a Digital SLR Camera?

Way back in the old days cameras had a thing called film.  Light would strike tiny particles of silver in this film and whenever more than a couple photons of light hit one of these silver grains it would be called exposed.  Exposed grains were soaked in a solution called a developer and they would then turn black.  The parts of the film that received the most light would have the most silver grains developed, and that part of the film would be blacker than the rest.

One problem was that if a grain was developed, whether by two photons or by a thousand photons, the entire grain turned black.  So the resolution of the film was limited by the size of the silver grains, and in order to have a good resolution, like what we call today pixels, the film size had to be as large as possible.  The most practical size for film for good pictures  was 35mm, and thus the most popular camera was called the 35 mm camera.

Now the 35mm camera took pictures that were good enough that people wanted to see exactly what they were filming before they pressed the shutter.  Cheaper, smaller format cameras had a viewfinder that was offset from the lens, so it looked at a slightly different part of the world than the camera lens, so there was some guesswork involved in what exactly would show up on the film.  The solution was to place a movable mirror right in the middle of the main camera lens.  This mirror would move out of the way when you pressed the shutter, but until then, it would deflect the light that would normally fall onto the film up to the viewfinder so you could see exactly what would fall onto the film.

The motion of this mirror was called reflex, and because there was only one main camera lens – instead of a camera lens plus a viewfinder lens – the cameras were called single lens reflex, or SLR.  Almost all of those cameras exposed 35mm film, meaning that the size of the exposed film was 35mm across.  Every part of the camera, from the body to the lens to the distance of the lens from the film, was designed specifically to make an image of the outside world onto a 35mm long strip of silver grains.

Fast forward to the 1980s and 1990s.  Innovations in design and manufacture of light sensitive semiconductor arrays made possible small chips with at least 640 by 480 individual light sensitive regions, which was as good as or better than most commercial camera film of the same size.  This availability of cmos and ccd led to an entire generation of small consumer cameras; remember that both the lens, the body and the geometry of a camera revolves around the size of the film, and in this case these chips compared in size to 8mm or 16mm film, much smaller than 35mm.

These small form cameras featured a viewfinder like their old small film type cameras:  the viewfinder was offset from the camera so it showed a slightly different picture than the film, or in this case the chip, saw.   But the new cameras were now digital, so they read the amount of light at each point, or pixel, of the chip and converted that amount of light into a number; the digital cameras could display this digital image on a small screen, so the photographer could preview exactly what the chip was seeing.   Previews on the back of the camera gave these small form cameras the major advantage of SLR with the convenience of inexpensive consumer point and shoot cameras, and today these cameras comprise a large part of the consumer electronics market.

Small point and shoot cameras, like the popular Canon Digital Elph series, routinely shoot pictures of far better resolution and clarity than the old consumer cameras of similar sized film.  The ubiquity of excellent picture quality with the convenience of computer and internet connectivity have truly revolutionized consumer photography and its ability to be shared with much larger groups of people than just friends or family.   Still,  there is a constant demand in digital products for improvement in all of the specifications, and these demands for even better image quality motivated a whole new generation of digitial cameras.

These new cameras are called digital single lens reflex, or DSLR, cameras, and they are almost exactly like the old fashioned 35mm SLR cameras, except they use a larger 16mm or 35mm sensor chip instead of film, and some makers have taken the opportunity to redesign their removable lenses.   Some cameras can still use the lenses made for older 35mm film cameras, but other cameras need their own brand of lenses.  Still, almost all DSLR cameras have removable lenses so that the photographer has a choice of lens format, from macro lenses to telephoto zoom lenses.

The larger format DSLR cameras have other advantages over the point and shoot digital cameras, but whichever camera you choose you can be sure that it exceeds the image quality of most all of the last generation consumer cameras.