Part 1: Budget, SLR vs. point-and-shoot, and resolution
Part 2: Exposure controls (program modes, shutter speed, aperture, white balance, and ISO)
Part 3: Light meters, lenses, image stabilization, autofocus, and flash.
Buying a digital camera involves balancing lots of competing features and parameters. Your goal is to find a camera that provides the shooting controls and image quality you need for your intended results, in a package that’s comfortable to use and easy to work with. And, of course, your final decision has to be something that you can actually afford.
In the first two installments of this series, you’ve worked your way through a series of questions aimed at helping you cull the huge field of digital cameras down to a few models. You’ve made most of the core decisions, including price, resolution, size, and photographic controls.
At this point, you’re more than halfway there. Now you’re ready to look at light meters, lenses, image stabilization, autofocus, and flash.
Meter Reader
Whether you prefer to let the camera make exposure decisions for you in its fully automatic mode or like to exercise your own judgment by using some form of manual mode, a good light meter is essential to getting a properly exposed image. Though it’s possible to get into geeky, technical arguments over the merits of one light metering system or another, the fact is that these days, just about any camera from a reputable manufacturer is going to have a good-quality, sophisticated light meter.
Unfortunately, evaluating a light meter’s performance can be a little tricky in camera stores. You need to try the camera out in the mixed lighting situations that can hamstring even a good light meter. So, to learn about light meter performance, you usually have to turn to camera reviews and user reports, all of which are readily available on the Web.
What you can assess first-hand are a camera’s metering modes. Most cameras include one or two modes, and though you can usually get by with a good matrix meter (sometimes called a multi-segment meter or a segment meter), a couple of extra modes can be handy for dealing with trickier lighting situations.
A matrix meter works by dividing your image into a grid, metering each cell of the grid, and then calculating an average metering that works for the whole scene. Matrix meters are good for just about any situation, and the metering algorithms that most vendors employ can handle even difficult mixed-lighting situations.
Nevertheless, there are times when a matrix meter will underexpose the foreground — for example, if you have a bright window or landscape in the background. For these instances, a centerweight meter — which works just like a matrix meter, but favors the center cells in your scene — can help you get a correct exposure that doesn’t leave your foreground elements in shadow.
A spot meter is an essential tool for any photographer who wants to ensure that specific parts of the image are exposed in a particular way. For situations with an extreme range of dark to bright areas, a spot meter can help you avoid overexposing the highlights in your scene.
Your ideal camera doesn’t necessarily need all of these options. But do think about which metering options you need for the type of shooting you want to do.
Most cameras use a through-the-lens (TTL) metering mechanism. This means that the light meter actually looks through the camera’s lens when reading your scene. A TTL meter has the advantage of being able to correctly meter, even if you’ve attached filters or special lenses to your camera. Though less common, some cameras use a light meter that’s external to the lens. In rare circumstances, external meters can be confused and deliver inaccurate meter readings.
Through a Lens, Sharply
When choosing a camera, it’s easy to get hung up on resolution and image-processing controls as the final arbiter of image quality. But if your camera has a lousy lens, all that extra resolution and image-processing power doesn’t count for much.
To evaluate a lens, you need to be able to see output from the camera. The LCD on the back of a camera is far too small to judge lens quality or most potential image-quality problems. For a more accurate assessment of lens quality, you must view images on a computer monitor. If your local camera store doesn’t have a computer on which you can view test images, buy a media card that’s compatible with the cameras you want to test. You can take the card to the camera shop, shoot some images onto it, then assess the results at home. In addition, many camera review sites post full-resolution sample images you can download and examine.
For a point-and-shoot camera with a built-in lens, your lens evaluation task is fairly simple. If you’ve opted for a digital SLR, you’ll need to decide which focal-length ranges are appropriate for the type of shooting you tend to do: telephoto for sports and nature photography, wide angle for landscape photography, somewhere in between for general shooting.
Whether you’re choosing a camera with a built-in lens or a removable lens for an SLR, the evaluation issues are the same:
1. How good is the overall focus and sharpness? Can the lens render fine detail? Are the corners as sharp as the middle? Check throughout the camera’s zoom range — some cameras can’t maintain corner sharpness as you move to a wider angle. Also, shoot with a variety of apertures, particularly with wider (lower-numbered) apertures. As you stop down a lens, you will lose sharpness (even though depth of field will increase). Try to determine at what aperture the lens exhibits a noticeable drop in sharpness.
2. Does the lens vignette at wide angles? Vignetting is a darkening of the corners and sometimes the edges.
3. As you zoom the lens to either extreme, do you see barrel or pincushion distortion? That bowing of vertical lines either in or out is usually only a problem on extreme wide-angle lenses. Even if a lens has some slight distortions, they might not be a problem for everyday shooting.
4. Does the lens have a trouble with flaring; that is, colored circles and reflections that usually only occur at wide angles when shooting toward a light source? Flares are almost impossible to remove from your images later.
There are also some practical lens issues to consider:
5. Does the lens offer attachments? Many point-and-shoot cameras with built-in lenses let you add wide-angle or telephoto attachments that extend their focal length range. If you want this option, look for a bayonet style mount, which is much easier to use than a threaded mount. Note that some point-and-shoot lens attachments partially obscure the camera’s optical viewfinder, requiring you to use the LCD viewfinder instead.
6. Does the camera have an electronic or manual zoom control? A manual zoom control is always preferable for the speed and flexibility it affords. On smaller cameras, though, there simply isn’t room in the unit for a manual-zoom control.
35mm Equivalency
Digital camera image sensors are much smaller than a piece of film. (For more on this, see “Making Sense of Camera Sensors“.) As you change the size of a camera’s focal plane, the field of view of any given focal length changes. So, while a 50mm lens on a 35mm camera is roughly equivalent to the field of view of the naked eye, a 50mm lens on a typical digital camera is extremely telephoto.
Most point-and-shoot and mid-size digital SLR cameras have tiny focal lengths, usually between 8 and 20mm. However, because sensor sizes can vary, there’s no simple way of predicting how wide or telephoto 8 mm might be — the actual field of view of a given focal length can vary greatly depending on the size of the image sensor. Thankfully, most camera vendors do reveal the 35mm equivalencies for a camera’s focal length range. These numbers tell you what the equivalent range would be on a 35mm camera.
(For those of you not familiar with 35mm focal lengths: 50mm is about the same field of view and magnification as the naked eye; lenses longer than 50mm yield more magnification, and therefore a narrower field of view, while lenses shorter than 50mm yield a wider field of view.)
Unfortunately, digital camera vendors have adopted a convention from the video camera market and demarcate zoom lenses in terms of a multiplication factor — a 3x zoom or 4x zoom, for example. This isn’t a particularly useful piece of information, because it doesn’t actually tell you anything about the particular range of the lens. Does it start very wide and go 3x from there? Or does it start mid-range and go 3x from there, into a telephoto range?
Some vendors print 35mm equivalencies on the front of the lens barrel, but most include this information only in the camera’s manual, so you have to dig to discover the camera’s range.
If you’re shopping for an SLR, search the camera’s specifications for a “multiplication factor.” This is the factor by which you can multiply the actual focal length of a lens to determine its 35mm equivalent length. For example, the Canon EOS 30D has a multiplication factor of 1.6. If you stick a 50mm lens on the camera, it will have the same crop as an 80mm lens on a 35mm camera (50 x 1.6 = 80).
Many SLR vendors now make special “digital lenses” that are engineered to work with digital image sensors of a specific size. Basically, these lenses are engineered to project a smaller image circle that’s more appropriate to a small sensor. Because they don’t need to cover a full-sized 35mm sensor, they can be made smaller, lighter, and cheaper than a regular lens. But you’ll still need to multiply their focal lengths by your camera’s multiplication factor to determine their 35mm equivalent focal length.
Take note of the camera’s widest aperture (wider apertures have a lower f-stop number). A lens that has a really wide maximum aperture lets you shoot with shallower depth of field and use faster shutter speeds to stop motion.
Image Stabilization
Some lenses — both SLR lenses and lenses built-in to point-and-shoot cameras — offer image stabilization technology. (Nikon calls it “vibration reduction”). Most stabilization technologies work by making a lens elements — usually the one closest to the camera — movable. By rotating and pivoting the last element, the camera can bend the light passing through the lens to compensate for camera movement. If you jitter the camera to the left, the lens can bend the light a bit to the right to make up for the motion.
Good stabilization improves any lens and should improve sharpness in almost any shooting situation. However, stabilization is particularly useful for two situations.
When you’re shooting at extremely telephoto focal lengths, framing your shot can be difficult because it’s tough to hold the camera steady. With a stabilized lens, framing at long focal lengths is significantly easier.
Even more importantly, stabilized lenses let you shoot in lower light. Say you’re in low light and your light meter is recommending a shutter speed of 1/30th of a second. You’ll have a difficult time shooting a handheld shot that isn’t blurry. A lens with good stabilization can compensate. Some stabilization technologies promise up to three stops of stabilization. In other words, you can shoot with a shutter speed that’s three stops slower than what you could manage without the stabilized lens.
While modern image stabilization technology is startlingly effective, it’s not a substitute for a tripod. You can still shoot shaky, blurry images with a stabilized lens. But if you tend to regularly shoot in low-light conditions, image stabilization can greatly improve your shots.
Autofocus and Digital Zoom
All digital cameras these days come with autofocus mechanisms, and some are definitely better than others.
First, test a camera’s speed in achieving and locking focus. You don’t want to miss a fleeting moment because your camera’s slowly focusing in and out before deciding on the correct focus point.
Most cameras focus by measuring the contrast in a scene. Where there’s more contrast, there’s greater sharpness and therefore better focus. While such contrast-detecting autofocus mechanisms have a lot of advantages — they’re not limited by range, and they can work through windows — they can be fooled in low-light scenes where there is little contrast. I recommend a camera with a focus-assist lamp — an extra light that the camera can shine into a scene to create more contrast. If the camera you’re considering doesn’t come with a focus-assist lamp, find out if it can use its built-in flash as a substitute.
Many cameras offer multiple autofocus points — that is, they can calculate focus from different parts of the image, not just the center. These mechanisms make it possible for the camera to differentiate between foreground and background elements and focus accordingly. Test this feature by shooting tricky compositions. And because no mechanism is perfect, look for a manual override that lets you pick which autofocus point the camera will use.
Evaluating a digital zoom feature is a simple, one-step process: Don’t bother. Digital zoom mechanisms interpolate an image up to a larger size. Photoshop and other pro-level image editors will handle this much better in post-production.
Flash
Flash evaluation is more critical on a point-and-shoot camera than on an SLR because point-and-shoot flashes tend to have more problems. First, consider range. Small cameras have small flash units with flash ranges that are typically very short. A flash with less than a 10-foot range is not particularly useful.
Point-and-shoot flashes also tend to produce a lot of red-eye because they’re so close to the lens. To balance that, look for a camera with a red-eye reduction mode. Some cameras even include built-in red-eye removal. These features are easy enough to test in a camera store by taking shots of the eager camera salesman. (Who, upon seeing how thorough and knowledgeable you are, will become even more eager, with visions of selling you a really fancy camera. On second thought, maybe you should take a picture of an innocent bystander.)
Most low and mid-range SLRs include a pop-up flash. Because these flashes are fairly small, they don’t have great range, either — typically, 10 to 15 feet. But because they’re positioned farther from the lens, red eye is less of a problem.
For any camera with a built-in flash, look for flash-exposure compensation. This feature can make the difference between good and bad flash shots. Flash-exposure compensation lets you dial the strength of the flash up or down. It’s particularly useful for dark situations, which can cause many flashes to over-illuminate a subject (Figure 1).
Figure 1. The image on the left was shot with the built-in flash’s default setting. I toned it down by dialing in a flash exposure compensation setting of -.5 stops.
Serious flash shooters who want maximum flash flexibility should select a camera with an external hot shoe. Also, check out the external flash system. Does it provide TTL metering? How does it handle slaving?
Keep On Swimming
At this point, you’ve reduced the vast ocean of camera models to just a small puddle. All that’s left is to consider secondary features that might separate one camera from another, and to weigh image quality. I’ll tackle those secondary features in the next installment of the “Digital Camera Buying Guide.”
This article was last modified on December 14, 2022
This article was first published on June 26, 2006
Commenting is easier and faster when you're logged in!
