How To Choose A Digital SLR
What to look for...and look out for
Choosing a digital SLR is a bit trickier than choosing a film SLR because you have all of the film-camera considerations, plus a number of digital aspects to weigh. One benefit, though, is that you can't go wrong with any of today's D-SLRs—they all offer lots of features, good performance and enough resolution to produce quality 12x18 inkjet prints.
Some D-SLR models are better suited than others for specific tasks, naturally. Consider your needs. If you shoot 500 images every day in harsh conditions, you want a super-rugged, pro-model D-SLR. If you're a backpacker, you might want one of the smaller models. If you specialize in high-speed action sequences, you want a camera with a fast shooting rate. If your photography involves a wide variety of subject matter, though, most of today's D-SLRs will meet your requirements.
The size of the image sensor makes a big difference in how wide an angle of view a given lens provides. Smaller sensors "see" smaller portions of the image produced by the lens (see the illustration below). The Canon EOS-1Ds Mark II and EOS 5D have full-frame image sensors, meaning they're the same size as a full 35mm film frame (36x24mm). A given lens used on one of these cameras will have the same angle of view as when used on a 35mm SLR.
Other D-SLRs have smaller sensors. Fujifilm, Konica Minolta, Nikon and Pentax D-SLRs, for example, have APS-C-sized image sensors (about 23.7x15.6mm), with a 1.5x magnification factor-if you put a 100mm lens on one of these cameras, it frames like a 150mm lens on a 35mm SLR. So, if you specialize in wildlife and sports photography and like long lenses, a D-SLR with a smaller sensor magnifies the subject within the compositional frame. If you specialize in wide-angle work, you want a camera with a large image sensor, so it doesn't narrow the angle of view of your wide-angle lenses; D-SLR makers and independent lens manufacturers offer super-wide-angle lenses designed specifically for the smaller-sensor D-SLRs, however, so wide-angle fans can shoot truly wide-angle shots.
The size of the image sensor also determines how many pixels the camera has, or the size of the pixels. The larger the pixels, in theory at least, the better they are at gathering light, so you get better low-light and high-ISO performance, and a wider dynamic range. And all other things being equal, the more pixels an image contains, the greater its resolution—you get images with more detail and can make larger prints (or crop into an image and blow up a small section). Of course, all other things aren't equal. Image quality depends on many things besides pixel count, among them the sensor's dynamic range, the camera's A/D converter, its image-processing engine, the image compression used, the quality of the lens used for the shot, and how steadily the camera was held. Assuming the image is sharp (focused accurately, without camera shake) and properly exposed, all of today's D-SLRs produce sufficient image quality to run a shot across two pages in this magazine or produce a superb 12x18-inch inkjet print. Resolutions range from 5 to 16.7 megapixels.
Larger image sensors have their downsides. They cost a lot more, their larger surface areas seem to attract more dust, and for telephoto fans, they reduce or eliminate the crop factor. High-megapixel images take up lots of room on memory cards (you get fewer shots per card) and require lots of computer horsepower.
Some D-SLRs use CCD (charged-coupled device) image sensors, while others use CMOS (complimentary metal oxide sensor) sensors. Long ago, CMOS sensors weren't as good as CCD sensors, but the technology has certainly leveled the playing field, and CCD versus CMOS no longer makes a difference. Working pros use D-SLRs with CCDs and D-SLRs with CMOS imagers.