Inside the Camera
Today's SLR cameras pack a lot of technology into their small bodies. They house multipart viewing and shutter mechanisms as well as a host of electronic components that make such features as automatic focus and automatic exposure possible. You can't see the mechanism for many of these features — and for the most part, you really don't have to worry about them — but it's a good idea to know where they are and what they do.
Take the lens off an SLR camera body and you'll immediately see the single-lens reflex mechanism. This is the technology that separates SLR cameras from all others.
When you look through the viewfinder on an SLR camera, what you actually see is a reflected image that's been turned the right way around before it even reaches your eye. First, the mirror takes the image that shines through the lens and reflects it upwards to the translucent glass, which functions like a miniature projection screen. The pentaprism, located above or behind the glass, flips the image on the screen, making it appear right-side-up, and redirects it to the viewfinder window.
The single-lens reflex mechanism consists of a slanted mirror positioned between the shutter and the lens, a piece of translucent glass, and a five-sided prism or pentaprism. It allows you to see exactly what the image on the film will look like.
When the shutter is clicked, the camera quickly flips the mirror out of the way so the image is directed to the film or — in the case of digital cameras — to the sensors. As long as the shutter stays open, the mirror, which is connected to the shutter timer system, stays up. Because the mirror is moved out of the way, the image can no longer be seen in the viewfinder, but this momentary blackout is barely noticeable. Once the image is captured, the shutter closes and the mirror flips back down into place. This is the reflex motion that gives the camera its name.
On modern SLR cameras, viewfinder windows do more than simply facilitate framing and focusing. What you'll also see in the window, depending on the camera's particular features, are indicators for things like shutter speed, focus, red-eye reduction, flash, depth of field, and camera-shake warning, which indicates situations where handheld snapping will yield blurry images due to camera movement and slow shutter speeds.
Most SLRs have mechanisms inside that are called focal-plane shutters. These devices are basically a couple of pieces of flexible cloth or metal blades that expose the film or sensors by very quickly opening and closing when the shutter release is pressed. In conventional cameras, the shutter is positioned in the back of the camera, just in front of the film; in digital cameras, it is placed just in front of the sensor array.
Conventional SLR cameras all have internal film handling systems, consisting of a film holder to keep the film in place while it's being exposed and a film-transport system that controls how the film moves through the camera. Digital cameras make use of memory cards or sticks, which store the image until it can be uploaded to a computer, commercial print processor, or home printer. These memory cards can be erased and reused.
SLR cameras are sometimes very intimidating to beginning photographers, but they need not be once the basic principles are understood. Most SLRs can be used in automatic mode until the photographer grasps the fundamentals of aperture and shutter speed.
