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Digital SLR Camera
Digital Single Lens Reflex Technology (SLR)
SLR cameras are the one type of cameras that will never be made as slim and small as the digital cameras. This is because they use a quite sizable mirror system to help you obtain the picture you need. Instead of using an electronic viewfinder it has to have a mirror box to hold the lens mechanism.
The mechanism is pretty complicated. What happens is that you see the actual picture as if it was captured and for this reason it has been a prominent tool for amateur and pro photographers and still is. The light shines through a series of lenses in line than onto a mirror positioned at about 45 degrees. This directs the light onto a focusing lens through which it enters a prism which after a series of reflections returns the image to your eye. When you press the button to expose, the mirror set at a 45 degree angle moves upward so that it lay against the focusing lens. This allows the light to pass under it onto the actual film, taking the exact picture you saw.
The main difference between old and new is of course the replacement of film with a memory card. Apart from this parallax free view finding is built in. This means that any distortion from the angles of view will be compensated for. The key factor for the usability of DSLR cameras is that all facilitate interchangeable lenses. This is not a unique feature but one that made them very popular. Another feature that also makes SLR cameras more usable is the fast phase detection autofocus that can create a virtually lag free LCD screen. The reason they use it chiefly in DSLR is that it requires a special sensor placed in the pictures path.
Of course all other advantages of digital systems affect the camera. You can easily preview, and edit basic things in photos, create folders and also use simple retouching features inside the camera. Photos can now be stored on the overall much cheaper media cards and physically stored in a much smaller place. Any changes made can be viewed in an instant so the process of photographing is faster, or at least allows you to concentrate on what is more important.
Four Thirds System
For the digital age they have managed to compress all this into smaller spaces, namely through the four thirds system developed by Olympus and Kodak. Instead of the 36mm x 24mm sensor sized used in traditional 35mm film cameras they implemented a 18mm x 13.5mm sensor which is considerably smaller. Detail that is lost with this however is compensated by superior optical quality.