Digital SLR cameras are the top of the line for photo enthusiasts and most pros, although there are some very high-end cameras above the digital SLR in the photography "food chain."
They employ a mirror and pentaprism system that allows the viewer to see "through the lens" in the viewfinder exactly what they will be photographing. This differs from compact cameras and newer mirrorless cameras which, by contrast, have an electronic viewfinder that renders a "picture" of the picture which is usually viewed on the LCD screen, although some do still have viewfinders.
Another common element of DSLR is that they are similar to 35mm cameras in format and sensor size. This simply means that the pictures taken will be about the same size and quality as 35mm film cameras. It is the standard by which digital cameras are measured.
Professionals and serious enthusiasts will normally use digital SLR cameras as their main camera rather than compact digital cameras. The reasons are simple. The image quality, performance, and controls are simply better.
When shooting digital, the image sensor generally determines the quality of the photo. Many people mistakenly think that the image quality is a result of a certain number of megapixels, but that is not true at all. It is the physical size of the sensor that has more influence on quality.
When you compare an image sensor in a digital SLR cameras to that of a compact digital camera, you will discover that there is a huge difference. For comparison, we will look at a Canon EOS Rebel T3 and a Canon PowerShot SD980IS. Each has about 12-megapixels of picture power. The image sensor of the T3 measures 22mm x 14.8mm, but the PowerShot sensor is a mere 6.17mm x 4.55mm. You could fit almost 9 PowerShot sensors on one T3 sensor. This difference gives manufacturers the ability to put much better, high-quality pixels on the larger sensor.
Digital SLR cameras in their own category are not created equal either. There are a few different sizes of sensors within the DSLR category. Some cameras are considered "crop sensor" cameras while others are "full frame" cameras. Again, the larger sensors in the full frame cameras produce better results.
Since about 2003, there has been a revolution in the digital SLR world. That is when the first sub-$1000 splashed onto the market. Since that time, technology has improved vastly and the price of better cameras has tumbled. Now, you can purchase an entry-level digital SLR for under $600 while getting a very well-featured mid-range camera for about $1500. Pro models still cost more, but as the old saying goes, "You get what you pay for!"
However, lower prices may not be the only reason for the sudden popularity and increase in digital SLR owners. These cameras have become so popular that many more families now have them as their main family picture machines, and even children are carrying them and doing a wonderful job of taking photos.
The reasons for this are two-fold (in addition to the price reduction, of course). First, the technology has improved tremendously in the past couple of years. They are so easy to use that even a child can do it. And secondly, there are so many more individuals and families sharing their experiences by way of photography on the social media sites, such as Facebook.
Digital SLR cameras are no longer the intimidating cameras that they used to be. They are user friendly and economical.