Immediately after the light moves through the lens and enters the camera, it reaches a mirror. The mirror reflects the light to a five-sided prism, known as a pentaprism. The combination of the mirror mechanism and the pentaprism make up the basic, central aspect of SLR cameras. The fact that the pentaprism reflects the light multiple times means that the image is corrected. That is, it appears in the viewfinder exactly as it does in the world, rather than being reversed as most mirror images are.
Typically, SLR cameras are activated by pressing the shutter release button. When this happens, the mirror flips up, creating an unobstructed path between the lens and the now open shutter. The light travels through the lens, past the shutter, and reaches the image sensor, which captures the photographic image. A separate shutter closes, whilst the mirror returns to its original position and the first shutter resets.
This entire process takes place in under a second, allowing the camera to preserve a highly precise image that is close in time to the moment the camera is activated. The mirror and pentaprism combination also gives the photographer a clear preview of the final photograph.
The mechanism at the heart of an SLR camera is the image sensor, as this is the device which actually catches and preserves the photographic image. Image sensors measure and record the amount, intensity, and hue of the light which passes through the lens and the shutter. To do so, they make use of multiple smaller devices. These devices typically include a lens, a signal amplifier, and an analogy to digital converter.
Most SLR cameras contain image sensors that are larger than the ones found in typical compact digital cameras. This allows SLR cameras to take pictures that are similar in quality to traditional film formats. In particular, they have similar depth of field, color quality, and picture angle.
Understanding the SLR digital camera requires examining each of its components and their role in creating the photographic image. One final component is the internal computer contained within the camera. This allows for in-camera processing of the images, which can include basic tasks such as removing noise and grain as well as eliminating red eye.