Photograph by numbers (continued)

Of megahertz, megapixels, and myths
Perhaps the biggest source of confusion for potential digital-camera buyers is the megapixel rating. What does it mean? How important are these megapixels? Do more of them mean the camera is better? As with anything high-tech, the answer depends. Taking a cue from computer companies, which long ago decided megahertz (the clock speed of a processor) was the best way to sell computers, digital-camera marketers have conveniently distilled the value of their products down to megapixels. Unfortunately, consumers are getting only part of a camera's story or, worse, are being pushed into buying super-powerful models they don't need and can't afford.

Simply put, the number of megapixels refers to the amount of data (mega = one million; pixel = the smallest unit of data expressed in an image) that a camera's image sensor can collect. If you want large, high-quality prints (eight-by-10 or larger), or plan to do a lot of image editing (which can delete image data), you should buy a camera with a resolution of five megapixels or higher. Creating large prints from image files with smaller amounts of data may result in prints that are blurry or blocky. But if you want only to view your photos on a computer, to send them via e-mail, or to make the occasional print, stick with a camera in the three-to-four-megapixel range.

To further confuse matters, some cameras with a lower number of megapixels capture higher-quality images than do comparable cameras with more megapixels. How? Because of differences in the size of the camera's image sensor. The individual photosites in large image sensors typically can capture more image information per photosite than the sites on a smaller sensor. Thus, even if a small sensor has five megapixels, a larger sensor with only three megapixels may be an equal, if not better, performer.

When confronted with a salesperson (or advertisement) raving about the latest 20-megapixel D-SLR, remember that the whole of a camera is greater than the sum of its parts. The number of megapixels is only one aspect of a digital-camera imaging system, which consists of the lenses, image sensor, analog-to-digital converter chip, and other digital guts. More important, dozens of megapixels are meaningless if the camera's other features don't meet your needs.

Voodoo ergonomics?
Amid all this talk of megapixels, image sensors, and whatnot, it's easy to lose sight of one of the more obvious aspects of buying a digital camera: ergonomics. Do you have large hands that fumble with small controls? Do you want a camera you can slip into your shirt pocket or small bag, or are you unwilling to sacrifice camera control for a smaller form factor? Go to your local electronics superstore or camera shop and handle the cameras. Find a model that feels natural in your hands and has controls that are easy to use. Remember that the more pro-like features a camera has, the bigger it will be. While it might be nice to earn neighborhood bragging rights with a camera that possesses every feature known to science, those extras mean nothing if you can't access them in time to catch baby's first steps.

View to a ... shot While evaluating usability, also take time to look at the camera's LCD (liquid-crystal display) - that small-but-revolutionary electronic screen on the back of most digital cameras. In addition to composing shots, you can use the LCD to instantly review, delete, or in some cases even edit your shots, all completely in-camera. If your eyesight is less than perfect or if you plan to shoot mainly outdoors, make sure the LCD is large and bright. Try the on-screen menus. Are they logically placed and easy to navigate? Look at cameras with an LCD that flips away from the camera body, or tilts, which can be helpful when you need to take photos at awkward angles.

And don't overlook the optical viewfinder. Usually located above the LCD, the optical viewfinder (also known as the eye-level viewfinder) is made of glass and gives a direct view of your shot, without digital intervention. Some camera manufacturers don't include an optical viewfinder in their cameras, which means you're forced to use the LCD in shooting conditions when a steady hand is key (low light/low speed, for example). Because you have to hold the LCD several inches away from your face to see the images on the screen, it's harder to keep the camera still. In such situations, you're better off peering through an optical viewfinder, which forces you to keep the camera (and your arms) close to your body. Steadying the camera in this position is easier, especially if you keep your elbows tight against your sides. Using an optical viewfinder also doesn't drain battery power, which LCDs suck up like Kool-Aid.

Note to those who wear eyeglasses: some optical viewfinders also contain a small control called a diopter, which allows you to adjust the viewfinder focus so you can get the shot without fumbling with your specs.

Through the looking glass Entire family trees have been wiped out by the epic battles waged over who makes the best camera lenses. I'll conveniently sidestep the issue by saying if a digital camera is made by a reputable film-camera company that uses quality lenses (Canon, Nikon, Olympus, etc.), it's probably a good bet.

The most important lens fact for digital-camera newbies to know is the difference between digital and optical zoom. Though a manufacturer may claim an unbelievable zoom power of 48x, that inflated figure indicates the digital zoom, or a mix of digital and optical. Instead of physically zooming in on the subject with the lens, digital zoom employs electronic wizardry to crop out a portion of the shot and then increase the number of pixels, something you can do to digital photos with most image-editing software. Because the camera is, in effect, throwing away data, the result is poor image quality. Read the fine print to find the optical-zoom rating, and avoid using digital zoom.

Control freak
Digital cameras offer the same amount of control over settings and shooting modes as their film cousins do. And as with film cameras, how much control you have over specific settings, such as shutter speed and aperture, depends on the price of the camera. Generally, the more expensive the camera, the more control it offers. Lower-end cameras automate most of the work.

Film photographers making the switch to the digital realm will find familiar film-camera modes and functions, including exposure bracketing (or auto-bracketing), aperture priority and shutter priority, ISO values, and preprogrammed modes for various shooting scenarios including portrait, landscape, low light, and sports (high-speed subject). The added benefit of digital is that it can augment the capabilities of these settings.

A good example is film speed, which is expressed as an ISO value (100, 200, 400, etc.). Digital cameras use ISO-equivalency ratings, but instead of expressing the light sensitivity of film, the ISO-equivalency values in digital cameras actually represent the amplification of the electronic signals emitted by the image sensor, which is also known as gain. With a digital camera you can adjust the ISO value shot by shot to get just the right exposure, instead of burning through an entire roll of film while hoping you picked the right film speed. If you don't like the shot, you can delete it and try again with a different setting.

In motion
Because digital and video cameras are based on similar technology (an image sensor captures light and motion, then converts the electrical impulses to usable digital information), many digital cameras are capable of recording short movie clips. If this is a feature you find compelling, check a camera's specifications to see if it has video capability. The movies are saved in common, cross-platform computer video formats, including AVI, MPEG, and Apple QuickTime (.MOV), that you can download and view on your computer.

Know that despite using similar technology, digital and video cameras are different beasts. Just as video cams don't take great still images, the video that your digital camera records will be low-resolution, meaning you're not going to capture a 30-frames-per-second high-definition stream to display proudly on your 52-inch plasma HDTV. At most, the clips recorded by digital cameras are novelty items suitable for posting on the Web or playing on a PC. Some digital cameras can also capture audio while recording movies, but like the video, the sound quality is low. Expect to hear constrained mono versions of your Uncle Ned singing "Goodnight, Irene."

The amount of video you can capture is limited by the amount of memory in your camera and by its particular video capabilities. Budding mini-cinematographers should buy one or two high-capacity, high-performance memory cards and an extra battery.

Photographs and memories
All this wonderful digital-image data I've been describing has to go someplace, and in digital cameras that place is the memory card. Memory cards fit into narrow slots in the side of the camera and come in a variety of types, brands, shapes, sizes, and storage capacities - so many, in fact, that figuring out which memory card is which can be as confusing as sorting out all the different camera models. Does it matter which type of memory card your camera uses? Not surprisingly, the answer is "maybe."

Some memory-card types are more expensive than others, or more common, or save images faster. CompactFlash (Type I or II) is by far the most common and inexpensive memory-card type. Secure-digital (SD) cards are gaining in ubiquity, having the added advantage of being used by many portable electronic gadgets such as PDAs and portable MP3 players. So if you have a few of these gadgets lying around, you might want a camera that uses SD memory cards so you can swap a single card among various devices. The Memory Stick is also popular, but only because Sony devices are popular - Memory Sticks can be used only in Sony devices. They are also expensive.

Memory-card storage capacity is expressed in megabytes (MB), just like desktop-computer memory, and ranges from 16MB all the way up to four gigabytes (one gigabyte = 1000 megabytes). When budgeting for a digital camera, you should factor in the cost of a new memory card. To keep the retail price of a camera low, manufacturers often include a low-capacity card, typically only 16MB. That's a paltry amount of storage, especially if you're going to take memory-eating high-resolution images, or even video. You'll want to upgrade immediately. For the average non-pro consumer, 256MB or 512MB cards offer the most value. As of this writing, Amazon.com sells a 512MB CompactFlash card for $46, a 512MB secure-digital card for $50, and a 512MB Memory Stick for a not-so-cool $100.

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