Choosing a Digital Camera

1. Megapixels (MP).  The first thing mentioned in digital camera ads is the camera's resolution in megapixels. A megapixel is 1 million pixels; and pixels are the tiny dots that digital pictures are made of.  The more megapixels, the more detailed the image but the more expensive the camera. What you need depends on what size prints you plan to make.  The rule of thumb is that you need 2-3 megapixels to make a decent 8x10 print (the largest size that most computer printers can make).  For 4x6 or 5x7 prints, email, and Web pages, 2 megapixels is more than enough.  Even the least expensive cameras now being sold have 2 megapixel resolution and thus are adequate for most amateur purposes.  Higher resolution cameras (4 MP and over) are more expensive ($300 and up) but can give larger prints (11x14). The disadvantage of higher resolution is that the pictures take up more memory and therefore the camera and removable storage media can hold fewer pictures than a lower-resolution camera.  However, most high-resolution cameras allow you to choose a lower image resolution, which will increase the number of pictures that you can take.

2. Zoom range.  Most digital cameras come with a zoom feature that lets you change the image magnification.  For example a 3X zoom lets you increase the magnification 3 times, so you can zoom in on a distant object.  Zoom is especially good for outdoor photography.  "Optical zoom" is the best.  Sometimes cameras will also specify a "digital zoom" range, but that is unimportant because it is simply equivalent to cropping the picture (and thus reducing the resolution), which you can always do after-the-fact using your photo editing software.  ("Total zoom" is just the optical zoom times digital zoom). Some cameras have an extended optical zoom range of  x10 or even more; is such cases a tripod or some form of electronic image stabilization (e.g. "Steady Shot") is necessary to get sharp pictures.

3. Automatic or manual exposure control.  All digital cameras have automatic exposure control; that is, they change their lens opening and shutter speed automatically in varying light conditions. Most, except for the simplest and least expensive, allow manual control also, so that you can compensate for unusual situations or intentionally underexpose or overexpose for creative purposes.  A useful feature on some cameras is the optional "spot metering" mode, which allows you to optimize the exposure setting for a specific spot on the subject; this is good for backlit subjects (dark subjects in front of a brightly-lit backgrounds) that would othersize be underexposed by the standard autoexposure metering.

4. Automatic or manual focus control.  Some very simple cameras are preset to focus on a specified range, perhaps 6 feet to infinity, and are not adjustable. Most digital cameras have "autofocus", which usually uses a small spot in the exact center of the scene to automatically focus the camera's lens. This works fine when there is something in the exact center of the scene that you want to be sharply focused. Autofocus typically does not work well in low-light situations. The better cameras also have manual focus, which allows you to override the autofocus when it does not do what you want. ( Tip: One important factor is the speed of the autofocus; if it's too slow it will create a slight delay between pressing the shutter button and the instant when the picture is actually taken.)  

5. Color balance.  Different lighting situations may influence the color cast of the picture; for example, indoor incandescent lighting is yellow/orange; fluorescent lighting may be greenish; outdoor shade on a sunny day can be blueish. Although all digital cameras automatically set white balance to compensate for these color casts, some let you override the automatic setting. Some cameras allow you to manually set white balance by aiming the camera at a white surface and pressing a white balance button. Other cameras give you a choice of white balances for different lighting situations, e.g. for sunny, incandescent, fluorescent, cloudy, and flash light. For most purposes, standard automatic color balance is fine; any slight corrections can be made after-the-fact using your photo editing software.  

6. Removable storage.  Different cameras use different systems for storing images.  The most common system uses one of a number of different types of "flash cards", small removable cards that store your pictures electronically.  Flash cards come in several different types and sizes.  You must use the type that is compatible with your camera.  Once your storage card is filled up with pictures, you have to replace it with an empty one or return home and download your images to your main computer's hard drive before you can re-use that storage card.  The smallest-capacity cards (the ones often supplied with the camera when you buy it) sometimes hold only 8 or 16 pictures (depending on the resolution of the pictures).  You will probably want to buy one or more cards of a larger capacity (e.g. 128 Mbytes or 256 Mbytes), particularly if you plan to take a lot of picture when you are away from home and can't get to your main computer to download pictures.  Or you can carry a portable battery-operated hard disk or a laptop computer to download pictures when your flash card fills up.  A few cameras use 3.5" CD-R disks as removable storage. These store about 200 Mbytes, are very inexpensive (about $0.50 apiece), and can be read by any standard PC with a CD-ROM drive. This approach is the most convenient and affordable for heavy-duty photoshoots and traveling, because you can easily pack enough of these disks to hold thousands of pictures.  Plus, you can send pictures to friends and family via email or webshots.com directly from the mini CD-R disks when you are using cybercafes and other computers in public places (which probably won't permit you to download pictures into their machines). CD-R disks are non-eraseable, which insures permanent archival storage. 

7. Cost of required accessories.  Many digital cameras are sold stripped-down, without certain accessories that you will eventually need.  For example, many cameras are sold only with non-rechargable batteries that drain very rapidly, so you may want to buy re-chargable batteries and a battery charger (buy at least two sets of batteries, so one can be charging while you are using the other).  Also, digital cameras are usually sold with only a single removable storage device, usually of the lowest capacily, which may only hold 8 or 16 pictures.  Factor the cost of extra ones into your purchase price.  

8. Size and weight. Digital cameras can be remarkably small and light; the smallest ones are usually point-and-shoot models with 2x or 3x zoom.  However, if you are an experienced amateur who is accustomed to 35 mm film cameras, you may want one of the more advanced or professional models, particularly those with a large zoom range, that feels and acts more like a classical 35 mm camera.  

9. Ease of use. This is an important but ultimately subjective factor.  In general, point-and-shoot cameras are the simplest to operate and are relatively inexpensive; they provide 2-3 megapixel resolution, fully automatic exposure and focus (some - but not all - provide manual controls as well), and most provide modest zoom (x3). More advanced cameras and professional cameras are much more flexible, but they have many more buttons and controls, which may require that you spend more time reading the manual to learn how to use them - and also increases the chance that one of the controls may accidently be set incorrectly. If you are in doubt, I suggest starting out with an inexpensive point-and-shoot camera at first and then, if you want or need more, migrate to a more advanced camera when you know what features and capabilities are important to you.

10. Speed of operation. The delay you experience between pressing the shutter button and actually capturing the image is called the refresh time.  It occurs because the camera clears the image sensor, sets white balance to correct for color, sets the exposure, and focuses the image. Finally it fires the flash (if it's needed) and takes the picture.  The second delay, the recycle time, occurs when the captured image is processed and stored on your removable storage card or disk. This delay can range from a couple of seconds to as much as half a minute.  The higher the resolution, the slower the recycle time (because there is more data to store). Try out some cameras before you buy to see if these delays are bothersome. (Some more advanced camers have a "burst mode" that allow you to take a quick sequence of several shots by holding the shutter button down; good for fast action).  

11. More information. For a very nice illustrated introduction to choosing a digital camera, go to http://www.shortcourses.com/ A good place to compare features and prices of various digital cameras is http://www.digitalcamera-hq.com/.      (c) Tom O'Haver (toh@umd.edu), November 2003