Advantages

• An SLR camera allows the photographer to see through the lens with an accurate and large viewfinder. The photographer can quickly focus the subject, meter the light conditions and compose the image with very little lag time between shots or exposures. With a film camera or digital camera, the photographer can preview the light before recording the image.
  
  With non-SLR cameras, the photographer sees through a smaller viewfinder and does not see the image through the lens.
  
  

Versatility

• Most SLR cameras accept interchangeable lenses of various focal lengths such as a wide angle 18 millimeter lens or a super telephoto 500 millimeter lens. Photographers can enjoy this tool's versatility and creatively control the image. Certain smaller SLR cameras with a fixed lens will not allow this lens exchange.
  
  

Mechanics

• As light rays travel through the lens barrel, the camera's reflex mirror reflects light up to a five-sided prism known as the pentaprism that reflects a bright image to the viewfinder. When the photographer pushes the shutter button, this mirror flips up briefly and the shutter opens to record the image on the film plane or image sensor.
  
  The SLR camera can deliver sharp image quality even in low ambient light. Most high-quality SLR cameras include a depth of field preview that allows the photographer to see the acceptable range of focus.