Before we go much further, it’s probably a good idea to explain what an SLR actually is. SLR
is short for “single lens reflex,” and it refers to a class of cameras that rely on a mirror in the camera body to determine where the light goes, to the viewfinder or to the image sensor.
SLRs address one of the most serious shortcomings of point-and-shoot cameras: the fact that
light can’t generally go to two places at once, so as the light goes through the lens and on to the
sensor, the optical viewfinder is out of the loop. As a result, the optical viewfinder in most digital
cameras can’t show you the exact image that the camera is about to photograph (though the LCD display on the back of the camera gets its image from the sensor, so it does reflect the image you’re about to capture). So, as you can see in Figure below, the mirror in a D-SLR reflects the light from the lens to the viewfinder using a collection of mirrors. But when you press the shutter release, the mirror flips up and out of the way, allowing the light to travel straight back to the sensor. After the image is exposed, the mirror moves back into its original position, so you can see through the viewfinder again.
Of course, because the mirror blocks the light from reaching the sensor before you take
the picture, it means you can’t preview a picture in the LCD display on the back of the camera
before you take the photo. D-SLR users must use the optical viewfinder to compose a photo,
while point-and-shoot users can choose to use either one.
It’s also worth pointing out that even this seeming immovable law of photography—that the
LCD can’t be used to compose photos when using a D-SLR—is changing. Some new cameras
(like the Olympus E-330) are using clever technology, like a mirror assembly that reflects some
light to the sensor and some to the viewfinder, allowing you to use the LCD all the time. Time
will tell if this kind of thing catches on.
Many folks are reasonably satisfied with a kit lens that’s often included with the camera
purchase. These lenses vary, but frequently they’re zoom lenses with a range like 80–200mm.
That’s not a bad range for what many photographers refer to as a “walking-around lens.” What
it’s missing, though, is wide angle—and believe it or not, you’ll need a wide lens a lot more
often than you need telephoto. After all, think about the kinds of pictures you frequently take. I
bet you do a lot indoors. If so, then 80–200 will be close to useless. Here’s what’s in my personal
Lens - What It’s Good For
12–24mm - Very wide angle photography. Good for tight corners indoors, capturing lots of people in a crowded room, and special effects in which the photo’s perspective is a little skewed, since 12mm is so wide that it looks a bit unnatural.
18–200mm - Several manufacturers sell an 18–200mm lens now, and it’s possibly the most
perfect walking-around lens ever made. It covers all the most common focal lengths you need day-to-day and while on vacation, so it could easily be the only lens you own.
100mm macro - If you like macro photography, a macro lens in the 100mm range is ideal for
a lot of common close-ups, and it’s long enough to get small insects like bees and butterflies without getting so close that you bother them. When you’re not shooting close-ups, this lens is a handy short telephoto.
80–400mm - Granted, this is a massive zoom, but I’ve used it for years to pull in distant
wildlife as if it were in my backyard. If you do wildlife or sports photography, you’ll want a big zoom that goes well beyond 200mm.
I recommend that you read lens reviews on the Web. Here
are some sites I highly recommend: