CNET digital SLR buying guide

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.

Some newer dSLR models incorporate a Live View mode, which allows the photographer to use the LCD to compose shots the same way you can with a snapshot camera. These modes 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, and you usually must focus manually when in Live View mode.

Types of digital SLRs

Interchangeable-lens full system digital SLR
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 ability 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 prosumer and professional models that we like best.

Fixed-lens digital SLR

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. 
Example: Olympus E-20N

SLR-like or SLR-style

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. These cameras are sometimes called ZLRs. 
Examples: Sony Cyber Shot DSC-R1 and Canon PowerShot S3 IS

Digital SLR vs. prosumer digicam

Advantages	Disadvantages
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, ultra-wide-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, recent consumer models from Canon and Pentax are about as light and compact as the larger EVF cameras.
Almost always better image quality at a given resolution. In other words, 5 megapixels from a digital SLR beats 5 megapixels from a typical digicam. This advantage is especially dramatic at higher light sensitivities (ISO 400 and greater). (For more on the reason for this, see page 3.)	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 can't use the LCD for framing. When you are composing with most digital SLRs, the mirror is bouncing light to the viewfinder, so no image is falling on the sensor. This means that you can't use a typical digital SLR's LCD for composition--it's for playback only. A couple of exceptions to this are Olympus's Evolt E-330 and Panasonic's Lumix DMC-L1.
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. film SLR

Advantages	Disadvantages
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--CDs or DVDs, usually--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 ability 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.
	Dust. It inevitably accumulates on the sensor, which makes you think twice about changing lenses, tests your Photoshop correction skills, and may lead you to nerve-wracking adventures in cleaning fragile and frightfully expensive microelectronic surfaces.

Sensor types

Start shopping for a digital SLR and you quickly find yourself entangled in a rat's nest of claims about sensor types and sizes, not to mention an entire alphabet of acronyms. Here's a breakdown of the basic sensor types.

CCD (charged-coupled device)
Currently 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.

CMOS (complementary metal-oxide semiconductor)
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 sizes

Nearly 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: 13.5mm by 18mm
Example cameras: All Olympus dSLRs, Pansonic Lumix DMC-L1

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 XTi, Nikon D80, Sony Alpha DSLR A100, 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 II, Canon EOS 5D


Geek note
Larger sensors are the secret to why 5 megapixels from a digital SLR beat 5 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 answer
Any 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.

Focal-length multiplier

We 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, or lens conversion factor, which requires a brief lesson in camera optics:

Example: On a Nikon D200, 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 D200. 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 D200, 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" lenses

Another 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. 
Manufacturers: Canon, Nikon, Pentax, Sigma

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

Other notable lens features 

FEATURE	ALSO KNOWN AS	WHAT IT IS
Image stabilization	IS (Canon) VR (Nikon) OS (Sigma)	A mechanism in the lens detects and counteracts camera shake, reducing blur in handheld shots at slower shutter speeds. Note that Sony, Pentax and Olympus offer an alternative to lens-based stabilization by incorporating image stabilization into the camera body. This allows you to use optical image stabilization with any lens.
Ultrasonic focusing	USM (Canon) AF-S (Nikon) HSM (Sigma)	Virtually silent piezoelectric motors provide the best focusing speed and responsiveness.
Apochromatic correction	UD (Canon) ED (Nikon and Olympus) APO (Sigma) LD (Tamron)	Special--and expensive--glass is used in one or several of the lens elements to counteract an optical defect called chromatic aberration, which can noticeably reduce sharpness, especially in telephoto lenses, and cause color fringing along high-contrast edges.

As with standard digicams, digital SLR features and performance vary widely. These are some of the most important differentiators.

Resolution	Low end: 6 megapixels High end: 16 megapixels
Frame rate	Low end: about 1.5fps to 2fps High end: 10fps
Burst depth	Low end: 4 to 6 shots High end: 110 shots
AF speed and tracking	Hard to quantify, but there are wide gaps in the AF performance of current digital SLRs, especially when tracking moving subjects. The top-end sports and news pro cameras definitely outperform the rest.
Ruggedness	Also hard to quantify, but another area where a wide gap exists between low-end offerings and the top sports and news pro cameras, which are sealed against moisture and made with more durable materials.
Viewfinder coverage	Low end: 90 percent High end: 100 percent
Start-up, playback, and mode-switching times	Low end: 1- to 6-second delays High end: Virtually instantaneous
Viewfinder information	Varies widely. The more information you can see without taking your eye away from the viewfinder, the faster you can shoot.
Quality of auto white-balance system	None is perfect, but a good one saves lots of time and headaches for JPEG shooters. Those who shoot raw files have the option of correcting white balance with software after shooting.
Ergonomics	Impossible to quantify--and partly a matter of personal preference--but critical to efficient shooting. Our advice: try before you buy.
Image stabilization	Lens or body? With respect to the final photo produced, both work equally well. Optical stabilization has the advantage of letting you see the stabilized version while you're looking through the viewfinder, which can be crucial when framing at long focal lengths (beyond 300mm), but putting the technology in the lens generally results in more expensive lenses. On the other hand, mechanical (sensor-shift) stabilization will work with any lens you buy, making it a less-expensive long-run solution.

Dabbler

I'm exploring photography as a fun hobby but getting serious enough for an SLR and a few lenses. I devote some of my time specifically to photography when I travel. I sometimes have my nephews and nieces pose for me at family gatherings, and I have several hundred pictures of the family cat. I'm thinking about taking a weekend photo seminar. I might make a 16x20-inch print of a great shot and frame it.

Price:	Less than $800 for body and starter lens
Resolution:	6 or 8 megapixels
Ruggedness:	Any
Frame rate:	2fps to 3fps
Burst depth:	5 to 6 shots
AF speed and tracking:	Low end to midlevel
Also look for:	Good image histogram; compact body smaller than 24 ounces; lightweight zoom lenses

Student

I'm studying photography and seriously thinking about it as a career. I'm trying out many different styles and disciplines: fine art, photojournalism, commercial, portrait, and wedding. I submit some photos to newspapers and magazines, and I print as large as my budget allows.

Price:	Less than $1,200 for body and starter lens
Resolution:	6 or 8 megapixels
Ruggedness:	Metal or hybrid metal-polycarbonate body; heavier-duty lenses
Frame rate:	2fps to 3fps and faster
Burst depth:	5 to 6 shots or more
AF speed and tracking:	The best you can afford
Also look for:	good image histogram; comprehensive viewfinder information display; good raw-conversion software; tethered operation; comprehensive flash-control features

News, sports, and action photographer

I'm a pro or a serious amateur who shoots breaking news; college or professional sports; or serious adult recreational leagues, competitions, and activities. My photos are printed in magazines and newspapers or posted on the Web. I might make prints as large as 16x20 inches.

Price:	As much as $5,000 for the body
Resolution:	8 to 10 megapixels
Ruggedness:	All metal, moisture- and weather-resistant
Frame rate:	8fps to 10fps
Burst depth:	40 shots or more
AF speed and tracking:	The best currently available
Also look for:	Extensive fast telephoto and high-speed AF lens lineup; simultaneous raw-plus-JPEG capture; excellent vertical-orientation controls; good image histogram; flexible white-balance controls; comprehensive viewfinder information display; comprehensive flash control features; solid battery life

Documentary, travel, or wildlife photographer

I shoot feature magazine assignments, long-term documentary projects, people and activities on the street, or wildlife and other nonlandscape nature subjects. My pictures are printed in high-quality, glossy magazines and books. Or, I make large prints for display in exhibits, at camera club competitions, or on my wall.

Price:	As much as $8,000 for the body
Resolution:	10 megapixels and greater
Ruggedness:	Metal or hybrid metal/polycarbonate body
Frame rate:	3fps or faster
Burst depth:	20 to 40 shots
AF speed and tracking:	Midlevel to top-notch
Also look for:	Simultaneous raw-plus-JPEG capture; excellent vertical orientation controls; tethered-operation capability; solid image histogram; flexible white-balance controls; high-quality raw-conversion software; comprehensive viewfinder information display; comprehensive flash control features; strong battery life; lightweight body and lenses for trekking in the wilderness

Studio, landscape, and fine art photographer

I shoot portraits and fashions; products for ads, catalogs, billboards, or eBay; and landscapes, close-ups, abstracts, and other fine-art subjects. My pictures might be shown on the Web, printed in a catalog, or made into a 4x6-foot poster in a clothing store. I make exhibition-quality prints in large sizes, 20x30 inches or bigger.

Price:	As much as $8,000 for the body
Resolution:	8 megapixels minimum; preferably 10 or more
Ruggedness:	All metal or hybrid metal-polycarbonate
Frame rate:	2fps to 3fps
Burst depth:	6 shots or more
AF speed and tracking:	Low end to midlevel, depending on typical subjects
Also look for:	Tethered operation capability; high-quality raw-conversion software; comprehensive flash-control features; a range of color modes, including new wide-gamut options

Wedding and event photographer

I shoot weddings, other kinds of parties, and sometimes youth sports team photos. Most of my pictures are printed at 8x10 inches or smaller, but occasionally I need to make a 20x30. I need a fast onsite work flow to help me make sales to friends, relatives, and other partygoers.

Price:	As much as $8,000 for the body
Resolution:	8 megapixels or more
Ruggedness:	All metal or hybrid metal-polycarbonate
Frame rate:	2fps to 3fps
Burst depth:	6 shots, but preferably more
AF speed and tracking:	Midlevel to top-notch
Also look for:	Excellent vertical-orientation controls; tethered operation capability; simultaneous raw-plus-JPEG capture; flexible white-balance controls; compatibility with decent event workflow software; comprehensive flash control features; solid battery life

Most standard digicams capture pictures in JPEG format only, but digital SLRs give you more choices. Here's a rundown of three important file formats:

JPEG

A lossy, compressed file format. Lossy means that actual image data is discarded to increase the compression ratio. 
Pros:

• Can achieve very large reductions in file size; the resulting smaller files take up less drive and media space and transmit much faster.
• Almost universally supported by imaging programs such as browsers. Sorting, viewing, and cataloging are quick and easy. 
  

Cons:

• Produces artifacts and causes loss of detail that may be difficult to notice at low compression ratios but gets progressively worse as compression increases.
• JPEGs are finished RGB images, meaning you have limited ability to alter or reverse the effects of in-camera settings such as white balance, tone curve, or sharpening.

TIFF

An uncompressed, finished RGB file format. 
Pros:

• No quality loss.
• Almost universally supported by imaging programs. 
  

Cons:

• Files are many times larger than even low-compression JPEGs.
• TIFFs are finished RGB images, meaning you have limited ability to alter or reverse the effects of in-camera settings such as white balance, tone curve, or sharpening.

Raw

The photographer's power tool--it's hard to overemphasize just how powerful they are. Raw files are minimally processed data from the sensor, which you convert to finished RGB images using special software on your computer. 
Pros:

• Highest potential image quality.
• Depending on your raw-conversion program, you can make extensive changes to image parameters such as exposure, white balance, tone curve, and sharpening.
• Typically about one-third the size of an RGB TIFF but with none of the information loss of a JPEG. 
  

Cons:

• Images are unfinished, so they need to be converted to another format for printing and posting on the Web, which is often a time-consuming process.
• Raw formats are proprietary and usually camera-specific and are often not supported by image editors and other software.
  
  

Hint: Think twice about any digital SLR that is not supported by a good raw-conversion program. If the camera's manufacturer doesn't make a decent converter, look for a third-party application. We've counted at least half a dozen for various digital SLR models. And many image-editing apps now include good raw-conversion features for a wide range of popular digital SLRs.

About colors

The ability to specify your image's color space is a common feature on digital SLRs. What's a color space? In this case, it's a defined range of available colors. The larger the range, the greater the color fidelity and richness your images have. Typically, you can choose between the two color spaces known as sRGB and Adobe RGB. sRGB corresponds well to the set of colors that a typical computer monitor can display. Adobe RGB includes more colors and is a better match for the range of hues produced by the offset printing machinery that is used to make magazines, brochures, posters, and the like.

Some digital SLRs include additional color modes or "looks," which offer different levels of color saturation, color emphasis, and contrast--similar to the varying looks of different films. If you shoot JPEGs and don't have time for a lot of Photoshop tweaking, these color modes can be a handy shortcut to getting the results you like. Most digital SLRs also allow you to create custom color modes by adjusting each of the parameters independently and saving them as a set.

Add-on flash

Good for: everyone. 
Unless you're wedded to available-light photography, a good off-camera flash, especially one with a head that can twist, can be invaluable when you've got a borderline exposure situation. It can help eliminate shadows, add catchlights to the subject's eyes in a portrait, and freeze action when you don't want to jack up the shutter speed.

Extra batteries

Good for: everyone, but especially for news and sports, documentary/travel/wildlife, wedding and event photography. 
It's a fact: digital cameras suck power, and digital SLRs suck more of it. A key component to good power management is having at least two batteries--one to shoot and one to charge. Having three is better: one to shoot, one fully charged spare on hand, and one in the charger.

Supplemental battery/vertical grip

Good for: news and sports, documentary/magazine/street/wildlife, wedding and event photography. 
Larger, more expensive digital SLRs typically have a vertical grip with a second shutter release built in for taking vertically oriented shots. Many smaller cameras are compatible with separate vertical grips that incorporate an extra or larger battery.

Filters

Good for: everyone. 
Use UV or skylight filters to protect your lenses, and use polarizers to increase contrast, cut reflections, and deepen the blue of skies. Some filters that were useful with film--color-correction and colored filters for black-and-white film--can now be duplicated with digital settings. There are also many special filters available for creating effects such as soft focus, star-shaped flares, and gradients. Many special effects can be applied in image-editing software as well, but some photographers find it more convenient to use a filter instead.

Lens hoods

Good for: everyone. 
Lens hoods minimize an optical effect called flare, which reduces the contrast and color saturation of your images and can create unintentional light artifacts in your images. No lens should be without a hood, and many come with them.

AC adapters

Good for: studio/commercial, event photography. 
Plug into the wall socket and forget all about exhausted batteries. Some sensor-cleaning methods require an AC adapter because it's a more reliable power source than batteries when you're holding the shutter open for extended periods of time.

Cable releases and remote triggers

Good for: sports and news, documentary/magazine/wildlife, studio/commercial, event, fine-art photography. 
A must-have for pretty much everyone, simple wired cable releases are great when you're using a tripod and want to fire your camera without shaking it. Fancier products, such as the PocketWizard and the Quantum Radio Slave, wirelessly trigger cameras and flashes from hundreds of feet away.

Wi-Fi transmitter

Good for: sports and news, event photography. 
Currently available only for some professional Canon and Nikon digital SLRs, this gadget mounts to the bottom of the camera and lets you transfer images via either the 802.11b or the 802.11g (Wi-Fi) wireless networking protocol. While you're shooting in the middle of the bar mitzvah, your pictures could be popping up on a computer manned by your assistant at the edge of the banquet hall. He takes lucrative print orders from adoring grandmothers while you keep shooting.