Digital Camera Primer
There are a lot of choices out there. Here's how to select the perfect digicam for you
(by Arthur H. Bleich)
Few things are more thrilling than shooting pictures with a digital camera and then -- with hardly any steps in between -- seeing them splash onto your computer screen and flow smoothly into your image editing program. It's the same as watching the birth of a photographic print in a developer tray in the olden days, or experiencing the chills that accompany unwinding still-wet negatives from a reel and holding them up to the light.
Of course, if you need a reason -- other than being on the cutting edge of photography -- to buy one of these cameras, consider the following advantages: instant image checking after you shoot, no scanning, no film costs (which encourages creativity), and promoting a cleaner environment. There's also still the historical significance of being among the pioneers to venture into new photographic territory. After all, only a few years ago no one would have thought that film would decline so quickly. Whatever your motivation, this article will acquaint you with the basics of digital photography.
No discussion about digital cameras and imaging can avoid the subject of resolution. Simply defined, resolution is the ability of a device to record fine details in an image -- like individual threads in a sweater or separate grains of sand on a beach. Images from digital cameras (and scanners) are made up of little squares (sometimes rectangles) called pixels. Pixel is short for "picture cell" or "picture element."
A digital camera's imaging surface is made up of rows of tiny individual light sensors that capture color and light information which is then electrically converted into digital data -- the cells or pixels that make up the image. If a camera is capable of capturing an image that consists of 2560 horizontal by 1920 vertical pixels, it is said to have a resolution of 2560 by 1920 pixels or 4,915,200 pixels (arrived at by multiplying the two dimensions). And rather than saying "4,915,200 pixels," you'd say "5 megapixel" because that is roughly five million pixels
The total sensor array is called a charge-coupled device (CCD) and is used on most digital cameras now on the market. However, some cameras are being built around complementary metal oxide semiconductor (CMOS) devices which are more reasonably priced and require very little power compared to CCD sensors but which, under certain conditions, sometimes produce undesirable electronic "noise" in the image.
The more pixels that can be packed into a given area, the higher the resolution -- resulting in a finer-detailed image. Think of it as using graph paper to help you draw a picture. The more squares per inch, the more nuances you'll be able to capture.
Optical vs. interpolated
Specifying digital camera resolution has become tricky lately because you have optical resolution, the actual number of sensors in the array, and interpolated resolution, which uses software magic to kick the optically obtained image to a higher resolution by artificially adding more pixels. Agfa used to ship PhotoGenie software with all but its lowest cost cameras, and the application did an excellent job of interpolation when images were transferred to the computer. Agfa claimed it used artificial intelligence, which sounded like a bit of hype but nevertheless it worked well.
Kodak used rectangular cells in some of their early digital cameras (like the DC120) which they then converted to square pixels. Thus a CCD consisting of 984 by 850 rectangular pixels would be converted to 1280 by 960 square pixels. The advantages of this were a smaller file size (greater storage capacity) and lower cost than offered by a CCD that had a full 1280 by 960 pixels. Vivitar took images from its ViviCam 3100, which used CMOS technology, and doubled them to a then whopping 1920 by 1600 pixels which gave customers larger pictures (or tightly cropped blown-up sections) that held together well, without degrading into individual pixels or "jaggies."
You can also interpolate a picture from a lower resolution camera within an imaging program, and this usually allows it to be blown it up to a larger size without losing too much quality. Experiment by using the Bicubic setting and then do a bit of sharpening or unsharp masking before you print it out. However you can only interpolate (or upsample) so much before your picture turns to mush -- and no amount of digital manipulation can make it any better.
The lens, Boss, the lens!
Resolution specifications are only a part of the story. A lot goes on after the shutter is pressed -- focusing, analysis of the scene for color temperature and exposure, light passing through the lens, analog conversion into digital pixels, image compression, internal storage, and more. Some cameras have been designed to integrate these processes so efficiently, they actually produce better images at low resolutions than others at higher ones.
The most significant factor in the quality of the final image is the lens -- you know, that tiny (on digital cameras) conglomerate of glass elements sitting in front of the sensor array. Imagine the precision needed to make a Nikkor f-2.4, 38mm to 115mm zoom (35mm equivalent) aspherical glass lens containing nine (count 'em) multi-coated elements in seven groups with macro, the diameter of which is the size of your pinkie -- and where the slightest aberration, acceptable in a larger piece of glass, immediately consigns it to lens hell.
Higher is better
Higher is better when it comes to digital cameras. Buy a camera with as high a resolution as you can afford if you want to make prints 11 by 14 inches or larger. Reasonably-priced digital cameras are now available in the 4 to 5 megapixel range that will easily satisfy that requirement. However, if your images are going to be displayed on a monitor (or printed not larger than 4 by 6 inches), then picture sizes in the 640 by 480 to 800 x 600 range is really all you'll need because most monitors display images at relatively low resolutions (72 to 110 dots per inch).
To figure out how big the image will display on your computer monitor, a bit of division is required. For instance, most Mac monitors are set so that 72 pixels in a row equal a linear inch. On PCs it's usually 96. So, on a Mac monitor, to find the length, in inches, of 640 pixels, just divide 72 into it and you get 8.8 inches. Do likewise with the short side of 480 pixels, and you end up with 6.6 inches. On a PC monitor it would display at 6.6 inches by 5.0 inches (640/96 and 480/96).
Given that 8.8 by 6.6 inches (or even 6.6 inches by 5.0 inches) is a pretty good screen size, if you plan to view images on your monitor or use them on the Web, a camera with a 640 by 480 pixel resolution should work nicely. It even gives you a large enough image that you can remove unwanted elements and still have a good chunk left over for viewing.
If image resolution happens to be higher than monitor resolution, the picture displays as larger-than-life because multiple monitor pixels are needed to form each image pixel. The only time image and monitor pixels become twins is when both have the same resolution. So remember, Web pictures shot at low resolution will look fine on a monitor. If their resolution is too high, it will have to be lowered in an imaging program so the picture can fit into its allotted space on the screen.
While low resolution images are fine for the Web, printing them on paper changes things drastically. You certainly can print that same 640 by 480 pixel picture as an 8.8 by 6.6 inch photo, but you may not be satisfied with the results. It depends on how fussy you are about picture quality. The picture might look fuzzy or have jagged edges -- called pixelization -- a phenomenon that occurs in low-resolution pictures when there aren't enough pixels to describe the range of color or detail in an image.
If you want to print pictures as large as 5 by 7 inches, the picture should have about 768 vertical pixels or more. Larger print sizes will usually require a picture with at least 960 vertical pixels. The vertical pixel number is the smaller one when resolution is described. But as I mentioned before, some cameras with lower resolutions may be able to produce the same results depending on the quality of their design. Incidentally, many cameras offer a choice of high and low resolution modes. Use the higher one if you want prints, and the lower one for Web images or for sending photos as e-mail attachments.
Higher is bigger, too
Of course, the higher the resolution, the larger the file size -- even though most images are compressed in the camera using JPEG (Joint Photographic Experts Group) encoding. At first, you'll probably want to save every gem you've shot, so expect your hard disk to fill up fast (a good reason to buy a removable drive, with plenty of cartridges). Your file sizes will depend on the specific image and the degree of compression.
Many cameras allow you to select the degree of compression depending on the ultimate picture quality you require. On a typical digital camera available compression ratios might be 1:4 (Fine), 1:8 (Normal), and 1:16 (Basic). In all modes, resolution remains the same. On some cameras, though, resolution also changes, so check the specifications. If a high degree of compression is acceptable, it allows you to store more images in the camera or on its memory card (more about this, later).
When an uncompressed image is opened, it will be roughly five to twenty times larger than its compressed size. A 640 by 480 pixel image compressed to 50K will inflate to about 900K when opened in an image editing program. A 1,024 by 768 pixel image compressed to 200K expands to 2.25MB. And when you get up to 1,280 by 1,024, a 900K JPEG mushrooms to 3.75MB. So you can see that multi-megapixel images can easily balloon to substantial sizes. And if an image also undergoes interpolation its file size can tax even today's massive hard disk space.
That's only the beginning. If you do any editing on images, you won't want to re-save them as JPEGs, because JPEG is a lossy compression method. This means that to reduce file size, some of the image information is lost; you can't get those pixels back without starting over from your original image (so always work from a copy, never the original). Instead, save images in the Tagged Image File Format, (TIFF or .TIF) with LZW lossless compression, if available, to save space.
To make it simple, bring the image into your imaging program and then, before doing anything, save it as a TIFF. Then you can begin working on it and it will always subsequently close and re-open as a TIFF, eliminating the risk of it being closed as a JPEG and becoming further degraded if you open it again to do some more work on it.
Patience is a plus
Let's take a little breather here. I'm a cat person and I always tell newlyweds to have cats before they have children (a biological impossibility, but you know what I mean). Cats teach you how to be patient and accept things on their terms. So will digital photography. If you love instant gratification, it will certainly provide you with that, but it will also teach you patience.
Years ago, the first time I transferred images from a digital camera through a serial port to my hard drive I was too excited to notice that each one took about 30 seconds. That doesn't sound like much, but when you transfer 40 exposures, that was a minimum of 20 minutes. Interpolation increased the time per shot even more. Plus, it took still more time to rotate those vertical shots upright so I didn't twist my neck out of shape viewing them. Today's fast USB connections transfer pictures much more quickly, but with the ever-increasing image sizes, you may still have to wait.
Then, once downloaded, you must separate the good, the bad, and the ugly. So far, there's no easy way to do this. The "digital contact sheet" displayed prior to downloading isn't -- as they say where I live --worth spit. The images are too small and you can't see detail. So, expect to end up transferring most of them. And when they're finally aboard, it's not easy to position them side-by-side on the screen without resizing them and fiddling even more.
All this is changing, of course. You'll soon be able to routinely transfer scores of images in a flash (literally) and software will eventually take care of positioning and selection. But for now, prepare to have your patience tested.
You'll need a photo imaging program to transfer and work with your pictures. Most digital cameras include plug-ins that you add to the program to simplify this process. Amazingly good image manipulation software is bundled with most cameras, but that doesn't mean that good stand-alone software shouldn't be given serious consideration as the packages are very inexpensive (under US$100), easy to learn, require only a small amount of RAM and hard disk space to run, and have many features photographers will appreciate.
While a plug-in is one of the easiest ways to get images out of the camera and into a program, many digital camera manufacturers are now including their own stand-alone programs that will allow downloading to a folder or directory. Some even have limited editing capabilities and, until you pick the digital imaging program you want to marry (divorce not being an easy option in this field), you can do a bit of refining with them and then print out your results. Some cameras allow you to bypass your computer entirely and print directly to one of the new six-color, photographic quality inkjet printers, such as the Epson StylusPhoto line.
Light sensitivity and time lag
Like conventional cameras where you can select films with different sensitivities to light, digital cameras in the consumer market price range offer various sensitivities to light, usually a film-equivalent ISO of 50 to 400. Almost all of them take perfectly acceptable pictures under low light conditions because their lens apertures are pretty fast, usually around f-2.8. As a standard feature, most have a built-in flash for really abysmal conditions and for filling in deep shadows on sunlit, high-contrast subjects. And when it comes to freezing action, some even have shutter speeds up to 1/16,000th of a second!
What you may find disconcerting, at first, is the slight time lag that occurs between pressing the shutter release and the actual exposure. That's when the camera spends a fraction of a second going through its pre-shot calibration and white-balancing act. But as a bonus, if you shoot under fluorescent lights, for example, you'll get perfectly color-balanced pictures instead of ghastly green ones. There's also some delay between shots while the camera processes and compresses the image. You'll quickly adjust to these quirks, though, and things are improving every day: some cameras can now even take multiple shots per second, although at lower resolution settings.
Shakes and screens
Even the best digital camera will seem like a poor choice if you can't keep it still when shooting. Favor cameras that have conventional optical viewfinders or through-the-lens reflex viewing, cameras that you can steady against your head to avoid camera shake. Cameras that provide only an LCD screen to view the image you're going to shoot may look nice sitting in a camera store, but they require that you hold the camera away from you to frame the shot, which creates unsteadiness and tired arms. Also, some LCDs wash out if you shoot outside with the sun at your side or back. Exceptions are cameras with viewing screens that swivel to allow you to look down into them while holding your elbows relaxed at your side.
Shakiness aside, cameras that have LCD screens, either integrated or as accessories, in addition to regular viewfinders are quite useful. They're great for checking the quality of pictures you've already taken and can help you pre-frame tight close-ups shots, preferably with the camera on a tripod.
Many cameras have a "video out" feature that allows you to view images on a television screen. This is handy, especially if you want to check a large view of your shots when you're traveling and don't have a computer handy. You can also use some cameras for presentations by pre-recording your pictures in the correct sequence on a storage card. Just make sure you buy an AC adapter if it's not supplied with the camera and remember that vertical shots will display as horizontals on the screen.
Batteries and storage cards
You will need rechargeable batteries and a charger if they don't come with the camera. Digital cameras used to eat batteries like candy (that was the #1 user complaint), especially since they must power the flash and the LCD screen used to preview and post-view shots (if the camera has an LCD). Things have improved a great deal, but it's still one of the weaker points. The best batteries for most digital cameras are Nickel Metal Hydride (NiMH), made by several manufaacturers.
Virtually all digital cameras use removable storage cards including Compact Flash, Secure Digital, xD-Picture Card, Memory Stick and others, but there's no established standard. Storage cards are a great thing because, in addition to being able to transfer images directly from the camera to your computer, they can also (with appropriate adapters) pop into an external card reader or directly into your PC's multi-format card reader for even faster cable-free downloading.
From autofocus to zoom
Even though the terms are not unique to digital cameras, let's define autofocus and fixed-focus (or focus-free). Autofocus cameras automatically and accurately pinpoint whatever you aim at and record it as the sharpest object in the picture. Fixed-focus cameras have their lenses fixed (or locked) at an arbitrary distance calculated to keep most everything acceptably sharp from a few feet to infinity.
Because lenses used on digital cameras are of extremely short focal length, they have extraordinary inherent depth-of-field, allowing subjects both near and far to remain in focus, even when the lens aperture is wide open. So if your camera doesn't have autofocus, it's not a big deal unless you shoot big close-ups with a fixed-focus lens or expose without flash under low-light conditions. Then subjects or objects in the foreground may appear unsharp. To compensate, some cameras have settings so you can manually shift the point of focus depending on whether you're shooting super close (macro), portraits, or general subjects.
Finally, zoom lenses for digital cameras now come in two flavors: optical and digital. To make matters even more challenging, some cameras incorporate both. On a digital camera with an optical zoom, the resolution remains the same regardless of the focal length you choose. But a digital zoom uses only part of the sensor array and, unless it is interpolated, ends up exactly as if you'd cropped the image -- and the resolution drops accordingly. A typical camera for example has a resolution of 2560 by 1920 pixcels, but using the telephoto mode or the sequence shooting mode may produce images that are only 1280 by 960. To put it simply, just remember: "Optical zoom, good; digital zoom, not so good," unless you're shooting only for the Web or for CD-ROM/DVD multimedia productions, in which case it doesn't matter.
Check image quality before you buy
Some camera manufacturers offer sample images on their websites. Make sure you don't print the images from within your web browser, though, because your output will be locked at the screen resolution of 72 or 96 ppi. Instead, download the files using the links provided at the end of the article, then open them in an imaging program of your choice. From there, print your samples at different resolutions and sizes to see for yourself how they'll look. It's a great way to see what you'll get before you buy.
Reading a book or two will improve your background knowledge of digital cameras and help you use one more effectively.