What makes an SLR?
The term SLR (single-lens reflex) is just a fancy way of saying that a camera‘s viewfinder looks through the same lens that exposes the image sensor (or film). SLR viewfinders show more accurately than a point-and-shoot camera’s viewfinder what the image sensor will capture, including the effects of any lens attachments.
As in any camera, the lens focuses light through a shutter and an aperture. But in a digital SLR, a mirror placed in front of the focal plane (where the image sensor sits) bounces the light that comes from the lens upward into a prism and then out the eyepiece. When you press the shutter button, the mirror flips up out of the way so the light can pass to the focal plane (see illustration, below).
Because light doesn’t reach the image sensor until you press the shutter, you can’t use the camera’s LCD as a viewfinder. Fortunately, most SLRs tend to have nice optical viewfinders that deliver good coverage, usually showing 95 to 98 percent of the final image.
In a digital SLR, a mirror placed in front of the focal plane (where the image sensor sits) bounces the light that comes from the lens upward into a prism and then out the eyepiece. When you press the shutter button, the mirror flips up out of the way so the light can pass to the focal plane.
In a digital camera, the RAM that is used to temporarily hold images while they are being written to the storage card.
Depth of field
A measure of the area of an image that is in focus, measured as the depth from the focal point of the image.
To avoid accidentally changing a camera parameter, some cameras require you to use multiple controls simultaneously to change a setting. This prevents accidental setting changes while carrying the camera.
The prism that sits on the top of most SLRs. The pentaprism transmits the light reflected upward by the camera’s mirror into the camera’s eyepiece.
APS-sized film sensors
Short for Advanced Photo System, APS film comes in a cassette that automatically advances to the first frame when you close the back of the camera. At the end of the roll, the camera rewinds the film back into the cassette and closes the film cover. Most digital SLRs use image sensors that are the size of a frame of APS film, rather than 35mm film. Higher-end SLRs use full 35mm-sized sensors.