So what is a digital SLR, anyway?
The term digital SLR is short for digital single lens reflex, so named because these types of cameras use a mirror positioned behind the camera lens to direct light toward the viewfinder when you're composing a photo. When you release the shutter, the mirror swings quickly out of the way, letting light from the lens travel straight to the sensor and momentarily blacking out the viewfinder. The viewfinder in an SLR incorporates a prism--usually a pentaprism--that flips the incoming image around so that you can see it right side up and bounces it onto the focusing screen where you see it.
The SLR design allows one camera to accommodate a very wide range of lens focal lengths, and that's the biggest reason that SLRs dominate serious photography. The explanation? With a non-SLR camera, you have to match the angle of view of the "taking" lens with that of the "viewing" lens. That's easy with a fixed lens or a short-range zoom, but it requires increasingly complex and expensive viewfinder mechanisms as you try to cover a wider range of focal lengths. With an SLR, you avoid this problem because the taking and viewing lens are one and the same.
Most dSLR models beyond entry-level models incorporate a Live View mode, which allows the photographer to use the LCD to compose shots the same way they can with a snapshot camera. The most basic implementations generally lock up the mirror, with the prism diverting the image to a small sensor that feeds through to the LCD rather than to the capture sensor. This does tend to hurt performance, however. Early versions required that you focus manually when in Live View mode, but current models use contrast autofocus.
Types of digital SLRs
These are what most people mean when they say "digital SLR," and they are the primary focus of this buying guide. As the name implies, the capability to remove one lens and replace it with another--to go from, say, ultra-wide-angle to supertelephoto--is what sets these cameras apart.
Examples: Almost all of the digital SLRs available today are of this type. Here you'll find reviews of the entry-level, prosumer, and professional models that we like best.
The lenses on these cameras can't be removed, which limits their versatility. The best known of these models use a semitransparent, nonmoving mirror to bounce some light to the viewfinder while letting most through to the sensor, which means you can use their LCDs for composing.
Examples: Olympus E-20N
These are standard digicams that use an electronic viewfinder (EVF)--just a small LCD--in place of an SLR's pentaprism or a point-and-shoot's optical finder. They can't truly be considered SLRs because they have no mirror, and we've yet to see an EVF that approaches the image quality of a decent pentaprism viewfinder. Most cameras of the type have extremely long zoom lenses and cameras are sometimes referred to as ZLRs or megazooms.
Examples: Megazoom
Also referred to as Hybrid cameras, these are models which use the same technology as point-and-shoots, but incorporate an interchangeable lens mount. The first "standard" to emerge in this market is the Olympus/Panasonic Micro Four Thirds joint technology venture. Like SLR-style cameras, they use an EVF, since they lack a mirror for an optical through-the-lens view.
Examples: Panasonic Lumix DMC-G1
Digital SLR camera pros and cons
Digital SLR vs. prosumer digital camera
These days, the consumer camera midrange consists of megazoom models--those bulky cameras with manual features and ridiculously long zoom lenses that looka lot like SLRs but are otherwise nothing like them when it comes to performance or photo quality.Advantages | Disadvantages |
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Greater lens versatility. Several manufacturers' SLR lens systems offer more than 40 lenses, each optimized for its intended purpose. Sample from a smorgasbord of zooms, ultrawide-angles, supertelephotos, and specialty optics such as macro and perspective-control lenses. | Generally bigger and heavier. The SLR mirror box and pentaprism add some weight and bulk compared to a point-and-shoot's design. Other factors include heavier, more durable materials and the need for larger batteries to power higher-performance components. That said, many recent entry-level models are about as light and compact as the larger EVF cameras. |
Almost always better image qualityat a given resolution. In other words, 10 megapixels from a digital SLR beats 10 megapixels from a typical digicam. This advantage is especially dramatic at higher light sensitivities (ISO 400 and greater). | Increased complexity. Choosing and changing lenses while shooting is an unwelcome chore for some folks. Plus, digital SLRs generally have a plethora of buttons and dials, which can intimidate some users. |
Better performance. Typically, digital SLRs have faster autofocus, shorter shutter delay, faster continuous shooting, and a bigger memory buffer. | Higher prices. While the least-expensive digital SLRs are now available at prices that compete with non-SLR cameras, the price range for digital SLRs is generally higher. |
Usually a more functional "shooter's" design. Some designs are better than others, but digital SLRs tend to have easily accessible thumb and forefinger wheels for exposure settings, discrete buttons for other critical features (exposure compensation, white balance), vertical position shutter releases, and just less menu surfing overall. | Generally inconvenient to use the LCD for framing. The introduction of Live View mode has made it possible to frame with a dSLR the way you do with a point-and-shoot model, but because dSLRs are signficantly bigger and heavier than your typical snapshot camera, and not really designed to be held at a distance in front of you, the process can be a bit awkward. |
Greater flexibility. Access to a much broader range of accessories, including powerful external flashes, alternate power sources, wireless transmitters, and remote triggering devices. |
Digital SLR vs. Interchangeable-lens camera
Interchangeable-lens cameras are similar to SLRs, but don't have the mirror an SLR uses to bounce the image up to the viewfinder. As such, they're theoretically smaller than their old-school counterparts.Advantages | Disadvantages |
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Better viewfinder With the possible exception of a live preview, the through-the-lens (TTL) optical viewfinders found on dSLRs are superior than the electronic viewfinders on ILCs and megazoom snapshot cameras. There's no update lag, regardless of lighting, and they're usable for shooting action; an EVF, which receives its image from the sensor, can only show you what's already happened, while an optical viewfinder, which passes the image straight through the lens, can show you what's currently happening. That makes it impossible to pan during continuous shooting. | No live preview in viewfinder An EVF can show you what the sensor sees, and therefore accurately display exposure, white balance and 100 percent of the scene. Some optical viewfinders can do the latter, but it adds a lot of cost to the camera. |
Fast TTL focusing speed For standard shooting, dSLRs use phase detection autofocus which is generally faster than contrast-detection AF, though not necessarily. | Slow Live View focus dSLRs use contrast-detection AF in Live View mode, which tends to be very slow. There are some fast implementations, usually by incorporating a second sensor, but this adds cost. |
Larger lens selection Simply by virtue of being a more mature technology, and because they can usually use older film-camera lenses without an adapter, there's a much bigger choice of lenses in all price ranges for dSLRs. ILCs can also use older lenses, but only via adapters and usually without support for autofocus. Plus, the large film and dSLR lenses tend to be uncomfortably bulky compared to many of the smaller ILC bodies. | No autofocus in video capture Though this should be rectified as time goes on, currently dSLRs don't support AF during video for a couple of reasons. First, the current crop of lenses aren't optimized to be quiet, which you need when capturing video. Second, most current dSLR lenses only support on-demand autofocus, rather than the continuous AF required by video. |
Size Though there are several very large ILCs and several relatively compact dSLRs, overall dSLRs are bigger and heavier than ILCs. |
Digital SLR vs. film SLR
Digital cameras have been around long enough that few people are really comparing them to film SLRs anymore, but we'll leave this here for nostalgia value.Advantages | Disadvantages | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Instant results. The instant review of your shots and the instant transmission capability (by e-mail or even via wireless transmitter, for instance) is the beauty of digital photography, regardless of whether the camera is an SLR or a standard digicam. | Greater initial expense. Feature for feature, digital SLRs tend to be two to four times more expensive than their film counterparts. | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Virtually no per-shot cost. There's no film or processing expenses. Flash media and disk space are reusable. Your archiving media can be counted as a per-shot expense, but it's tiny. | Larger and bulkier. Many digital SLRs are bigger and heavier than similar film cameras, although a number of newer models have narrowed this gap. | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Greater shooting flexibility. The capability to change ISO sensitivity, white balance, and a host of other image parameters from shot to shot. | Much greater power consumption. Digital SLR batteries are bigger, more complex, and more expensive. Plus, keeping them charged and ready is a critical part of your photography routine. All about digital SLR sensorsSensor typesCurrently the most common type of digital SLR sensor. Almost every dSLR manufacturer offers at least one CCD-based model. Pros: Traditionally, the highest image quality, pixel for pixel. Current sensors include innovative chip architectures designed to enhance dynamic range or speed. Cons: Most expensive. Most power-hungry. Initial implementations took advantage of CMOS' on-chip electronics to make cheap but noisy sensors. Stripping off the extra circuits increased each pixel's light-collecting area, thereby boosting sensitivity and quality to surpass that of many CCDs. Pros: Theoretically, lower production cost. Uses less power than CCD. Cons: CMOS sensors tend to be bigger than their CCD equivalents, resulting in larger cameras. The bottom line on sensor types Ignore the theoretical claims and judge the cameras, not the sensor types. We've seen great photos--and crummy ones, too--from digital SLRs with every technology. Sensor sizesNearly all digital SLR sensors are much bigger--and consequently much more expensive--than the thumbnail-size imagers in point-and-shoot digicams. Current digital SLR models use these sensor sizes.Four Thirds The specified sensor size for the Four Thirds format, an open digital SLR standard created by Olympus and Kodak. Dimensions: 17.3mm by 13mm Example cameras: All Olympus, Panasonic dSLRs APS A loose term for imagers that are approximately the size of the APS-C or APS-H film formats. Most digital SLRs use this size. Dimensions: Varies, APS-C (ranges from about 14mm by 21mm to 16mm by 24mm), APS-H (28.7mmx19.1mm). Example cameras: Canon EOS Digital Rebel XSi, Nikon D80, Sony Alpha DSLR-A350, Canon EOS-1D Mark III 35mm-film format Often called full-frame, to indicate that the sensor is the same size as a standard frame on a roll of 35mm film. Sensors this big are very expensive to build, but they eliminate the so-called focal-length magnification factor (see page 4 for more on this). Dimensions: 24mm by 36mm. Example cameras: EOS-1Ds Mark III, Canon EOS 5D, Nikon D3 Geek note Larger sensors are the secret to why 10 megapixels from a digital SLR beat 10 megapixels from a consumer digicam. To spread the same number of pixels over a larger sensor area, the pixels (technically, photosites containing diodes) must be bigger. These bigger photosites gather more light, so they produce less-noisy images, capture greater dynamic range, and perform much better at high ISO settings. So what sensor resolution do I need?The short answerAny current dSLR has sufficient resolution to handle Web or newspaper reproduction. For magazines and large print sizes (16x20 inches and greater), especially where you'll be cropping for detail, 8 megapixels is a good starting point. Fine-art landscape photographers and others seeking maximum detail should consider 10-megapixel-plus digital SLRs. The long answer Do the math. For example, let's say you're making an 8x10-inch print on an inkjet printer. Step 1: Figure out the required output resolution. Our inkjet printer produces best results at a resolution of 240 pixels per inch or greater. Step 2: Multiply the required output resolution by the linear dimensions of your final print. 8 inches x 240 pixels per inch = 1,920 pixels required for the vertical dimension 10 inches x 240 pixels per inch = 2,400 pixels required for the horizontal dimension Step 3: Multiply vertical by horizontal. 1,920 x 2,400 = 4,608,000, or 4.6 megapixels, is our minimum required resolution. Step 4: Accommodate some overhead for cropping. If you think you'll usually crop out about 30 percent of a photo, add 30 percent more pixels to the minimum required resolution. 4.6 megapixels x 1.3 = 5.9 megapixels Keep in mind: The math outlined above isn't written in stone; you can usually get good large prints even when you scale an image's resolution up in a program such as Photoshop. What about dust?Every time you change the lens, you run the risk of dust getting on the sensor, which at best can result in bad pixels you'll need to retouch out of your photos and at worst can muck up your camera's insides. Unless you shoot in very dusty, sandy, or otherwise particulate-heavy environments, and if you take reasonable care when you swap lenses, dust shouldn't be a huge worry; most cameras include a combination of antidust technologies, such as vibrating the sensor on startup to dislodge particles. If you are partial to shooting around dirt and sand, then you may want to search for discussions about the efficacy of various systems. Some sites, such as Chasseur d'Images, ran comparative tests in 2007 and concluded that Olympus had the only decent performance in this area. However, a year (or more) is a long time in a camera product cycle, and the results may have changed with subsequent generations of cameras.Digital SLR lens considerationsFocal-length multiplierWe already noted that most digital SLRs use APS-size sensors, which are smaller than a 35mm-film frame. This gives rise to a confusing notion variously called focal-length magnification, focal-length multiplier, crop factor, or lens conversion factor, which requires a brief lesson in camera optics:Example: On a Nikon D300, which has an APS-size sensor and a resulting focal-length multiplier of 1.5x, a 50mm lens captures the same angle of view that a 75mm lens would on 35mm film (50mm x 1.5 = 75mm). Since we're used to thinking about our lenses in 35mm-film terms, it's convenient to say that a 50mm lens "acts like" a 75mm lens when it's used on a D300. And a 28mm acts like a 42mm, a 200mm like a 300mm, and so on. It's an oversimplification--only the angle of view changes--but we won't squeal to the optics police. However, the focal-length multiplier doesn't affect the lens distortion inherent in a wide-angle lens. In other words, on that D300, a 33mm lens would have the same angle of view as a 50mm lens, but it would still have the barrel distortion characteristics of a 33mm lens--not the normal, portrait-friendly characteristics of a 50mm model. Pros: Sports and wildlife shooters love the way all their lenses seem to be longer than they were on 35mm cameras. Cheaper medium-range zooms work as if they were megabucks supertelephotos. Cons: Landscape and architectural shooters can't get lenses that are wide enough for their subjects--or they're forced to buy a very pricey superwide lens, such as a 14mm. If you find all this is maddeningly confusing, one option is to pony up the big bucks for a camera with a full-frame sensor, such as the Canon EOS 5D, so all of your lenses will perform just as they would on a film SLR. "Made for digital" lensesAnother brief lesson in camera optics:A lens projects a circular image towards the sensor. This image circle must be big enough to cover the whole area of the sensor; otherwise, you'll see vignetting, which is dark corners and edges in your pictures. Lenses for APS digital Some manufacturers make "digital only" lenses, which project smaller image circles--just big enough to cover the APS sensor frame but not big enough for the 35mm film frame for which previous lenses were designed. In theory, the companies can reduce size and weight and save money by doing this, but these lenses won't work on your backup film-camera body or on a future digital SLR with a 35mm-size sensor. Examples: Canon EF-S, Nikon DX The Four Thirds design: Unlike film, digital sensors can produce unwanted artifacts when light rays from the lens strike the sensor at oblique angles. One of the main selling points of the Four Thirds format is that its lenses will refract light rays to strike the imager close enough to perpendicular to avoid problems. We think the jury is still out on whether this issue is really significant or not. Manufacturers: Olympus, Panasonic
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