You are thinking to buy a digital SLR camera. You are unable to make a decision whether it is suitable for you. Then you should properly understand this camera before you spend money on it. Read this discussion further to clear all your doubts.
Mostly the digital single-lens reflex cameras use a pentaprism and mechanical mirror system for directing light from the lens to the optical viewfinder placed at camera back.
The DSLR uses a basic operation for viewing. Mirror reflects light coming from an attached lens at an angle of 90 degree upwards. Then it is reflected thrice by a roof pentaprism, and rectified for the eye of a photographer.
During the exposure, mirror assembly is swing upward, aperture gets narrows and shutter opens. This allows the projection of light from lens to an image sensor. After this a second shutter covers sensor, ends exposure, and mirror is lowered as shutter resets itself. The phase during which mirror gets flipped up is called viewfinder blackout. The fast acting shutter and mirror should be used to avoid delays during any action photo.
This process automatically happens over a time of milliseconds, and cameras are designed to achieve this 3 to 10 times every second.
Many professionals prefer these cameras as they have larger sensors than most of the compact digitals. You should note that DSLRs possess sensors generally close in size to the usual film formats. The large sensors permit similar picture angle and depth of field like the film formats. You also get higher signal/ noise ratio.
