What does SLR mean in a camera?

Answer 1

"SLR" means single lens reflex. What that means is that what you see through the eyepiece is directly through the lens - in other words what you see is exactly what you get. The way it works is that light comes in through the lens, 'hits' a mirror that bends the light up to a prism (typically a "pentaprism") that bends the light around and then out the back of the camera through an eyepiece to your eye. Light is amazing. When taking a picture, releasing the shutter will cause the mirror to lift up (and then if there's a focal plane shutter behind it to open that as well) allowing light to strike the film or digital sensor for the length of the exposure and then to drop down again at the end of the exposure. The primary disadvantage to the traditional SLR is that while the mirror is in the "up" position you can't see what's going on. The primary advantage was to frame your image exactly as you saw it and to be able to actually focus the exact image. And if you have a telephoto lens mounted, you're actually seeing what the lens sees, close up.

Prior to the invention of the "SLR" you had a few choices of how to view what you're taking a picture of. The most popular alternative was the "rangefinder" which is still available today and is used widely. The rangefinder's primary difference from the SLR is that you're not looking "through the lens" itself, but through a viewing window. And there would be a little "box" you would see in the window, that would define actually how much of what you see would wind up on the film (or sensor in a digital rangefinder). So even if you had a long telephoto mounted, then without special equipment you'd still see the same image in the viewing window, except the box would get smaller. Also focusing the camera differs in that in a rangefinder, there is usually a second smaller "window" off to one side, with a separate light source, that superimposes a second image on what you view through the viewing window, and by manipulating the focus ring on the lens, it aligns the two images to appear as one at which point theoretically if the camera is accurate enough, you are in focus. Also, when you release the shutter, you can still see what's going on; therefore if you're panning you can continue to keep the subject in the window box.

Answer 2

sorry late reply:D - super anon