What Does a DSLR Camera Mean?
The "SLR" of "DSLR" camera stands for single-lens reflex. Unlike a TLR (twin-lens reflex), this camera only uses one lens to focus and capture an image. The "D" simply stands for digital, meaning it captures an image with a digital sensor as opposed to film. DSLR cameras have more controls over exposure and focus than their digital point-and-shoot counterparts.
Pentaprism and Viewfinder
Point-and-shoot cameras are problematic when photographing subjects close up. The fact that the viewfinder is on one side of the camera body but the lens is in the center creates shifts in composition. The DSLR camera fixes this issue by using a pentaprism. Light enters the camera through the lens and bounces off a series of mirrors in the pentaprism, displaying the image in the viewfinder in its precise composition of how the digital sensor captures the image.
Unlike a digital point-and-shoot, DSLRs allow for precise focusing. You can either manually focus the lens or use autofocus, which you activate by tapping the shutter release button halfway. Most DSLRs automatically focus on what is in the center of the composition, though some others provide options to focus on other areas or to even keep the focus trained on moving objects.
DSLRs are built to accept a variety of lenses. Many come with a zoom lens such as a 28 mm to 80 mm lens that allows for both wide-angle and magnified compositions. Extremely wide-angle lenses, called fisheye lenses, are available to create spherical images. You can also acquire fixed focal length lenses that usually provide advantages in terms of wider aperture openings, allowing for quicker shutter speeds. DSLR lenses behave similarly to film SLR lenses, particularly if your DSLR is a "full-frame" model. This means the digital sensor is the same size as a traditional piece of film, so depth of field performs the same.
With a DSLR, you can choose your aperture setting through either a manual mode or a partially-automatic mode. Aperture choice affects how much of the depth of your composition is in focus. How wide your aperture will open, and thus how fast of a shutter speed you can use, is linked to your chosen lens. "Faster" lenses, due to their wider apertures, are more expensive than standard ones.
Shutter speed controls how long the shutter lets in light and is capable of freezing or blurring motion. Many DSLR cameras have a Bulb setting in the shutter speed that lets you keep the shutter open as long as you hold down the shutter release button. Shutter speeds of about 1/2000 of a second are standard for DSLRs, though more expensive models can go even faster.