Original link is at http://www.zdnet.com/zdhelp/stories/main/0,5594,2622552-1,00.html; For personal use only.
By Paul Worthington, Equip
Finding the perfect digital camera is a snap once you know the right specifications for your needs.
So you've decided to buy a digital camera. Congratulations!
However, if you haven't already figured it out, choosing a model that's right for you isn't as easy as going to your local camera shop and saying, "I want to buy a digital camera." Just as PCs are more complicated than typewriters, digital cameras are more complex than standard film cameras.
But we can help. In the following feature, we're going to teach you everything you need to know about digital cameras. When you're done, we're confident you'll be able to make an informed buying decision on the camera that best meets your needs
The sensor is the heart of all digital cameras. It's the electronic chip that takes incoming light and converts it to a digital file. The density of the sensor determines a camera's overall picture quality.
A camera has a
1-, 2-, or 3-megapixel sensor, which means that it has millions (the "mega" in
megapixel) of light-sensitive photoreceptor cells called photosites. The photosites take
the incoming light from the camera's lens and convert it to a digital file. The more
photosites you have on a sensor, the better your image resolution will be; and the better
the image resolution you have, the larger your final printed picture will be.
Most high-quality cameras today use a charge coupled device (CCD) sensor, while low-cost "entry-level" cameras use a complementary metal-oxide semiconductor (CMOS) sensor. CMOS chips are easier and cheaper to make, but they don't match the picture quality of a CCD.
Resolution refers to the number of pixels in a picture. Pixel stands for "picture element," and it is the smallest part of a recorded image. To better visualize what a pixel is, look at a color newspaper photograph under a magnifying glass. Do you see all the dots wedged close to each other? That's how pixels work (only the pixels in a digital photograph are much smaller).
VGA (Video Graphics Array) digital cameras are typically the least expensive cameras. The small sensor in a VGA camera captures just 300,000 pixels. These pixels are arranged in rows and columns. A VGA image has 640 rows and 480 columns of pixels, hence a resolution of 640x480. A 640x480 resolution image will look good on your computer or a web site, and it will print out a very nice 4 x 6 print. If you try to enlarge the print any further, you're going to see some image degradation, because there just isn't enough information in a 300,000 pixel image to enlarge a photo beyond 4 x 6.
XGA (Extended Graphics Array) and 1-megapixel cameras capture between 700,000 and 1.3 million pixels. A photo with this resolution will give you fine 5 x 7 prints—but, as we mentioned with the VGA cameras, a larger photo will suffer major image degradation. Because 2- and 3-megapixel cameras are what most people are interested in these days, XGA and 1-megapixel cameras have fallen in price. You should be able to find a good XGA or 1-megapixel model for $200 to $300.
Capturing 2 million pixels, 2-megapixel cameras have a resolution of 1600x1200 or higher. A 1600x1200 resolution image lets you print a good quality 8 x 10 image—so if you are looking for a digital camera that will give you the same quality and size prints as your standard film camera, we strongly recommend you buy a 2-megapixel camera. Because 3-megapixel cameras have been on the market for more than half a year, the price of 2-megapixel models has steadily declined. You should be able to find a good 2-megapixel camera for about $500.
Producing quality 11 x 14 prints, 3-megapixel cameras capture 3 million pixels. While most people aren't printing out their photos at 11 x 14, it's still good to have all that resolution because it allows you to crop your images and still maintain a high-quality image. Cropping is selecting a part of the original photo you want to keep and discarding the rest. For example, if you crop out one-third of a photo you took with a 3-megapixel camera, you would still have 2 million pixels left, meaning you'd still have enough resolution to make a high-quality 8 x 10 print. If you started with a 2-megapixel image and cropped one-third of the picture, you'd still be able to make a high-quality print, but only a 5 x 7.
Because 3-megapixels are the latest technology in digital cameras, you can expect to pay a premium for them. They cost about $1000—however, if you're not in a hurry to purchase one, 4-megapixel cameras will be here either by the end of this year or the beginning of the next. When 4-megapixels arrive, you can expect 3-megapixels to fall into the $500 price range.
Even though 3-megapixel cameras are at the top range of consumer models these days, digital resolution can go even higher. There are professional digital cameras that cost between $5,000 and $25,000, and they have sensors that capture 6 million pixels.
When we talk about a camera's optics, we are referring to the camera's lens, as well as the electronic and mechanical parts that focus the lens and open and close the shutter.
The lens:
This is in many ways the most important part of the camera for one simple reason —any
scene or subject that a camera photographs must first go through the lens. If you have a
poor-quality lens, it doesn't matter how many megapixels or other features a camera has:
The picture will be poor. Today's camera lenses are made of either plastic or glass.Today's digital cameras have a wide variety of focus options. If a camera has a fixed-focus lens, there are no moving parts in the lens' optical system: The lens is always locked in place, and it cannot be adjusted. A fixed-focus lens is OK for close-ups, normal shots, and landscapes, but it isn't necessarily great for any of these shots because it can't be manually adjusted to bring an object in the foreground into focus and to leave the background out of focus. A fixed-focus lens gives you fewer creative possibilities with your photographs.
Autofocus, on the other hand, means the lens system is motorized, and it automatically adjusts itself to take the best photograph—so you don't even have to lift a finger. An autofocus lens knows how far away an object is from the center of the camera's lens, and it will automatically adjust its optics to lock onto your subject and bring it into sharp focus.
As mentioned, there are going to be times when you may want an object in the foreground to be slightly blurred and the background to be in sharp focus. To achieve this and other effects, you'll want a camera with some manual-focus capabilities. There are two ways that digital cameras can handle manual focus. Some cameras have preset manual-focus modes, and some cameras are completely manual. In a preset manual-focus mode, you can choose whether you want the camera to focus on a distant landscape or a nearer foreground subject. Most cameras that offer this type of mode will give you four or five presets to choose from. If you need a little more control over your focus, you'll want a full manual focus on the camera. You can override the camera's autofocus controls with full manual focus by twisting the focus ring on the lens, which lets you focus the picture yourself. Generally, only professional-range digital cameras have full manual focus, such as Nikon's D1 (Kodak's line of high-end models) and Canon's digital EOS, which cost upward of $3000.
Zoom and Focal Length
A telephoto lens (or zoom lens, as it's often referred to) lets you adjust how close or how far a subject appears in your picture. Most cameras have two types of zoom capabilities: optical zoom and digital zoom. In optical zoom mode, the camera uses motorized lenses that move back and forth to bring the subject of your photograph closer or farther away from you.
With digital zoom, the camera takes a part of the picture the lens captures, enlarges it, and throws away the rest. The resulting picture is actually of lower quality since it is based on just part of what the lens and the sensor can capture. If you "digitally zoom" with a 1-megapixel camera, you'll get photos that have less than 1-megapixel of resolution - sometimes even half as much. Digital zoom is just a fancy term for what is no more than standard cropping; you aren't actually getting any "closer" to your subject. Our advice: Don't use it, and don't buy a camera that has only a digital zoom.
Focal length is basically the measurement in millimeters from the lens to the sensor. The distance from lens to sensor is what produces the wide angle to telephoto range you see when composing a picture and zooming the lens. A common focal length measurement today, for example, is 38-115mm. The lowest number in a focal length range is the lens' widest setting, and the largest number is the most close-up setting. Most digital cameras today have a 2x- or 3x-zoom lens—which means the second number in the lens' focal range is two or three times that of the first number. For example, if you fully zoom in on a subject with a 3x-zoom lens, your subject will be three times as large from when it was framed in the camera's widest setting.
Threads and Adapters
Many digital cameras have a threaded lens (like a screw), which lets you attach accessories such as filters and specialized lenses. The proper filter can improve the color and sharpness of a photograph tremendously, but filters are generally used by only professionals and dedicated hobbyists. Among the specialized lenses out there are teleconverters (or telephoto lenses as they're sometimes called), which multiply the focal range of your built-in zoom lens. For example, a 3x-zoom, 38-115mm lens would "see" at 57-152mm and be able to get six times "closer" to your subject. Wide-angle lenses let you photograph a wider area than a regular camera lens would normally capture.
For a properly exposed photograph, the camera's shutter needs to work in tandem with the camera's aperture. Together, they regulate the amount of light entering the camera.
The shutter is
like a curtain over a window. When it is open, light comes into the lens and hits the
camera's internal sensor. A camera with a fast shutter can capture fast-moving action,
such as a runner in a soccer game or a hummingbird's beating wings. If the camera's
shutter opens and closes too slowly, then your action scene will be blurred. A camera's
shutter speed is measured in thousandths of a second.
If the shutter is like a curtain hanging over a window, then the aperture is the window itself. An aperture is adjustable in size, generally with a circle of blades that open and close. A large aperture means it's wide open, so it lets the most light come in and hit the sensor. A small aperture reduces the amount of incoming light. If you're outside on a sunny day, a small aperture ensures you don't get an overexposed shot. Likewise, if you're shooting at dusk, you'll want to open the aperture all the way up, allowing in as much light as possible. A closed aperture in a dusk setting will result in a dark, underexposed picture.
Most digital cameras come with a handful of preset aperture/shutter combinations for different photographic scenarios. These presets are generally accessed through the menu settings of the camera. For example, the camera might have a "sports" preset, which means it will adjust the shutter and aperture to capture a fast action shot. A "snow and sand" setting adjusts the shutter and aperture to make sure that a photo taken in lot of light or against reflective surfaces is not overexposed.
To achieve greater clarity, artistic composition, and other interesting photographic effects for the best possible photographs, you need to master how the shutter and aperture work together. For example, you've probably seen a poster of a freeway or city at night in which all the buildings and bridges are in sharp focus, but all the cars' headlights and taillights seem to be strangely blurred. That effect is achieved by putting the camera on a tripod, opening the aperture, and keeping the shutter open for an extended amount of time. The cars are blurry because they're the only things moving in the photo - everything else, however, remains in focus.
Working in conjunction with the shutter and aperture is the camera's white balance. White balance helps control the overall color balance of your photo—it tells the camera what pure white is supposed to look like in pictures. Some types of lighting—fluorescent or incandescent, for example—can throw off the camera's color sensitivity, resulting in pictures in which the color is slightly off. For example, whites may end up with a blue tint. After you set the white balance for the specific lighting in the scene, colors should come out correctly.
Compression is shrinking the file size of a captured image down to a more manageable size. Most digital cameras use some kind of compression. An uncompressed image can be very large (between 8MB and 16MB), and since this is not practical (except on very expensive professional digital cameras), some form of compression needs to be applied to the image. The most universally accepted compression algorithm is joint photographic experts group (JPEG). The JPEG algorithm analyzes an image and throws out data that it thinks is nonessential to the picture. It doesn't throw away important details like buildings, people, or landscapes, but it does throw out the data that can't be perceived by human vision.
The only problem with JPEG is that it is a lossy compression algorithm. This means that some information is thrown away forever when the file is compressed—so if you compared the "uncompressed" image with the original, you would find some differences.
Most digital cameras have three types of JPEG settings: fine, normal, and basic. If you want high-quality prints, then be sure to set the camera to use the least amount of compression.
The fine setting is what is referred to as visually lossless, meaning the image is compressed to one-fourth its original size. When the photo is printed out, it will still look pretty good.
The normal setting compresses an image to one-eighth its original size. At this point, if you zoomed into the photo using a computer image-editing application, you'd see some pixelation and other artifacts.
The basic setting compresses an image to one-sixteenth its original size. We don't recommend this setting at all unless you plan to look at your photos on just a computer. If you snapped a photo using the basic setting and printed it out, it would look terrible.
Some cameras will let you save in both the JPEG and TIFF format. The TIFF algorithm, which reduces images to about one-third of their original size, does not apply as much compression to a photo as JPEG does, leaving your images with more digital information. TIFF photos require more storage, but they are higher quality. We recommend you use the TIFF setting if you have a lot of memory in the camera or if you plan on having your photos professionally printed.
Digital cameras hold photos in internal memory (generally a few megabytes of memory) or on removable media (small cards that go in and out of a slot in the camera and hold many megabytes of photos).
We recommend you choose a camera with removable media. With internal memory, once you've filled it up, you have to either download your images to a computer to continue shooting, or delete the images from the camera. With removable media, you just take out the full card and slide in a new empty one.
Most cameras that use removable media come with an 8MB or 16MB memory card. A 16MB card holds roughly 32 pictures at 1600x1200 resolution using normal JPEG compression. However, not all camera manufacturers use the same type of memory in their cameras. The following is a rundown of the different types of storage cards available today:
SmartMedia and
CompactFlash: Most digital cameras use either SmartMedia or CompactFlash cards. These
solid-state (meaning there are no moving parts inside) cards require no power to hold the
data, and they are only slightly larger than a quarter. SmartMedia cards are thinner and
cheaper, but CompactFlash cards have higher capacities. The highest-capacity SmartMedia
cards hold 64MB. The highest-capacity CompactFlash cards hold 160MB. An improved version
of CompactFlash, called Type II, allows for 250MB cards. 
Sony's Memory
Stick: In an effort to accommodate increasing image resolution (and to compete
with SmartMedia and CompactFlash cards), Sony developed a proprietary storage format
called Memory Stick. Memory Stick media is about the size of a stick of gum, and it can
hold up to 64MB of information. Right now, Memory Stick works only with Sony cameras and
Sony peripherals. 
Microdrive:
IBM calls its Microdrive the world's smallest hard drive. Unlike SmartMedia and
CompactFlash cards, Microdrive cards actually have moving parts inside. The advantages of
Microdrives are that they are incredibly small (they fit in a CompactFlash Type II slot),
and they hold an incredible amount of data. Microdrive cards currently hold up to 340MB,
but in the near future, IBM expects that number to go up to a full gigabyte. 
A liquid crystal
display (LCD) is the color, television-like display on the back of a digital camera that
allows you to see and frame the picture you're about to take. With an LCD display, you
don't have to read and interpret a light meter or guess at exposure settings: You see how
your shot's going to come out before you snap the picture.
One downside to an LCD is that it requires quite a lot of juice to operate, which causes your batteries to drain faster. Also, some older LCDs are unreadable in bright outdoor settings.
The main considerations when evaluating a camera's LCD are its size and its ability to both preview and review your images. As far as size is concerned, you'll want an LCD that measures at least 1.8 inches diagonally across the screen; two inches is even better. If you go smaller than 1.8 inches, you run the risk of encountering shot composition problems, because the screen is too small to reveal adequate detail. Additionally, a small LCD makes it difficult to read and access the camera's menu.
An LCD should have the ability to both preview and review your images, as well as allow you to see the shot you're about to take and play the shot back once it's been snapped. Some camera LCDs let you play only your images back. While this is better than not having an LCD at all, it means you're forced to use the camera's optical viewfinder for lining up your shots. And the optical viewfinders on most cameras aren't as accurate as LCD displays.
When we talk about the ergonomics of a camera, we're referring to a camera's size, weight, design, and how it generally feels in your hand. A digital camera can have the best picture quality in the world, but if it isn't a pleasure to hold and use, you'll never take any shots with it.
Size and Weight
Most digital cameras are small enough to fit in a purse, and many can fit in a pocket. None of them are so light that you'll forget you're carrying one, but only a few are so heavy as to cause muscle strain. Generally, there are trade-offs between size and weight. Larger, weightier cameras tend to have more features such as a built-in hot shoe (see the flash section), audio/video recording capabilities, a larger LCD, and a larger lens. Smaller cameras usually need to sacrifice features in order to maintain their form factor.
Look and Feel
Digital cameras come in many shapes and sizes. Some look like clunky old traditional film models, and others are sleek and futuristic. Although appearance can be important, the camera's feel is more important than its physical appearance.
Good cameras feel comfortable in your hand. Notice we said hand, not hands—you don't want to have to use two hands for every shot you take.
The best designs have natural grips for your fingers and a rest for your thumb. Buttons and other controls should be accessible to your index finger and thumb.
A camera's controls should be logically placed and properly laid out with intuitive icons that indicate what each button does.
And finally, the LCD should not be placed where your nose would naturally be positioned (when you're using the optical viewfinder); nose prints can leave your LCD an oily mess.
Digital cameras have a wide array of connectivity options. Here are the more important ones:
Most digital cameras operate on AA batteries, even though a few manufacturers use proprietary battery packs. Either way, digital cameras eat batteries faster than just about any other electronic gadget out there.
Flash
Most digital cameras have a built-in flash that has a range of about eight feet.
The flash normally has multiple modes of operation. These settings include: off, automatic, always on, flash fill (evens out a scene's lighting), slow sync (illuminates the foreground while letting the natural background light come through), and red eye (eliminates the glowing red pupils that sometimes occur when a flash goes off in someone's face).
If you want a flash with greater range or better controls, you need to add an external flash, or speedlight. If you add this type of flash, make sure your digital camera has a hot shoe (a track on top of the camera for an extra flash) Not all cameras have this feature, but don't worry about it too much; if you've never used one with your film camera, you're unlikely to need one on a digital model.
Special Functions
There are so many different digital cameras that it's becoming hard to distinguish one from the other, particularly if they're all using the same type of CCD sensor. To differentiate their cameras, camera manufacturers are designing models that do more than take pictures. Here are some of the more interesting features we're seeing in cameras today:
Miscellaneous Performance Issues
While we hope this feature has given you a clearer idea of what to look for when buying a digital camera, there are a couple of performance issues you won't be able to evaluate unless you play with the camera yourself or read a review in which certain issues are addressed:
Article backup; no commercial intention; not all links work. 09/02/2000.