Master Exposure Metering Modes

We demystify this underused feature and help you take better shots.

Dave Johnson

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Feature: Master Exposure Metering Modes

How well do you know your digital camera? You're probably pretty familiar with some of the features. No doubt, you've got the stuff like programmed exposure modes, image playback, and flash operation down cold. But how well do you know your camera's metering modes? Do you even know what they do? This week, let's dive into what is probably the most underused feature in digital cameras.

The camera's exposure sensor meter does the majority of the work when figuring out how to shoot a picture: It decides how much light is needed. That data is used to calculate how long the shutter remains open and how large the aperture will be. Not surprisingly, all exposure meters aren't the same--and some are better than others at metering a scene and applying the right exposure. Thankfully, most camera makers put several exposure meters into their cameras, and you can choose the right mode for any given situation.

Center-Weighted Meters

In the old days, most cameras came with a simple center-weighted light meter. This meter measures the light throughout the image, but applies more weight, or importance, to the central part of the scene in the viewfinder. The assumption--often a good one--is that you are most interested in the stuff centered in the picture, so the camera tries to get that part of the scene exposed properly.

Many digital cameras rely on this kind of meter for ordinary picture taking. However, it's the oldest and most inaccurate kind of meter around, so if you have a choice, I suggest that you avoid it in favor of the next kind of meter.

Matrix Meters

Often called matrix or multisegment metering, this kind of meter breaks the scene into multiple discrete parts and measures the exposure in each one independently. The sensor then collects all that exposure information and weights the relative value of each one based upon where it is in the photo.

The bottom line? Matrix metering is dramatically better than center-weighted metering modes at properly exposing a scene, especially one with high contrast or extremely variable lighting.

Even this approach can't provide perfect results in all cases: The contrast may be too great to achieve the ideal exposure in all parts of a photo. But if your camera has a matrix meter mode, you should use it most of the time, since it generally delivers outstanding results under a broad range of conditions.

Spot Meters

The last major kind of light meter is called a spot. You won't use this all the time; it's designed for special situations in which the matrix or center-weighted meter would lead you astray.

The spot meter is designed to measure light exclusively in the center of the image--traditionally, the center 1 percent of the screen. However, most digital cameras have less precise spot meters that read anywhere from 2 to 10 percent of the scene.

This meter can come in handy on occasion, but don't set it and forget it. A meter that only measures the light in the central 1 percent of the frame would typically take very poor pictures, either highly under- or overexposed depending upon the situation.

So when should you use the spot meter? Any time you're trying to photograph a scene in which a small subject must be exposed properly for the picture to work--and its lighting is different enough from the rest of the scene that you're worried it won't come out right otherwise.

Imagine, for instance, that you're trying to photograph someone who is standing in front of a brightly lit window. If you let the camera decide the exposure, the bright light from the window will radically underexpose your subject. So switch on the spot meter and expose the picture based on the subject. Yes, the window light will be overexposed, but that's okay--the important part of the picture is the person.

Switching to anything other than the standard matrix meter mode--especially the spot meter--usually works best when you also switch on your digital camera's exposure lock. This came in handy when I faced one of the trickiest photographic situations I've ever seen: a pair of white wolves playing near some trees, with highly contrasting light streaming into the scene. I tried a shot with the camera in its usual matrix metering mode, but I could immediately see that the image was badly exposed. So I switched to the spot meter, pressed the camera's exposure lock while I was focused directly on one of the wolves, and then recomposed to take the final picture.

Dave's Favorites: Make Music Videos With Muvee AutoProducer

I hear it all the time: "I'd love to connect my camcorder to the PC to make my own movies, but it sounds like a lot of work. Who has time?"

It's really not that hard to edit and produce your own home movies on DVD, but I will admit that you do need something of a passion for movie making. Otherwise, it's just a lot of drudgery: editing clips, putting them in the right order, adding transitions, titles, and music, and rendering the whole thing into a coherent film. And that does, indeed, take time... as well as a talent for filmmaking, which not everyone has.

Here's an attractive alternative: Use a program called Muvee AutoProducer to automate the whole process. Just load a bunch of video clips and add some still images, if you want. Specify digital music for the soundtrack, choose a style for your movie, then let it rip. The application analyzes the music and the images, then assembles it all in a surprisingly compelling way. What you get is a tightly edited music video that cuts between scenes at just the right moments to stay in sync with the beat of the music. In other words, you get a professionally edited music video.

Don't think that I'm exaggerating, either--the results are simply amazing. The Muvee application intelligently emphasizes scenes with human faces and keeps the feel of your production in line with both the musical selection and whatever style you chose. Some styles are tempo related, while others give your movie a certain look, such as sepia, black and white, or television. Styles can play with colors--a cinematic style punches up the color saturation while delivering the movie in wide-screen, for instance--and even vary the playback speed. The application also uses slow motion to particularly good effect. When you're done, you can burn your video to DVD, CD, or save it for playback on your PC.

You can try Muvee for free, but the full version of Muvee AutoProducer is a very affordable $50. If you'd like to do something interesting with your digital videos but don't want to master a video editor, this program is for you.

Q&A: What Is the Effect of Digital Zoom?

Recently, someone gave me a Canon PowerShot A300. It has a 3.2-megapixel sensor and a 5X digital zoom, but no optical zoom. In the past, you have said that "a digital zoom simply grabs a block of pixels from the middle of the scene and enlarges them." That leads me to a few questions. My first question relates to the equivalent 35mm focal length at various zoom positions. If the camera has a 33mm lens, what is the equivalent focal length when the zoom is set to 2X, 3X, or 5X? Secondly, what is the effect of the zoom on the resolution of my pictures? If the camera's highest quality mode is 2048 by 1536 pixels, what is the resolution when I shoot at a zoom setting of 2X, 3X, or 5X?

--Morris Taylor, Duncan, Oklahoma

Interesting questions, Morris. First, let's look at focal length. You can think of a camera's focal length as its magnifying power. Setting the digital zoom to 2X doubles the focal length of the camera to 66mm. Pushing it all the way to 5X gives you a 165mm lens; it's a simple linear relationship.

But as you know, magnifying power comes at the cost of resolution. When you push the digital zoom to 2X that means you have to divide both the X and Y dimensions of your image by 2. As a result, the image resolution is reduced to just 1024 by 768 pixels. At the extreme end of the digital zoom's range, your 5X image has an effective resolution of just 409 by 307 pixels--hardly enough pixels to paint a postage stamp. That's why I'm not a fan of digital zooms. Optical zoom systems, which move lens elements to magnify the scene, don't suffer from those kinds of problems.

Hot Pic of the Week

Get published, get famous! Each week, we select our favorite reader-submitted photo based on creativity, originality and technique. Every month, the best of the weekly winners gets a prize valued at between $15 and $50.

Here's how to enter: Send us your photograph in JPEG format, at a resolution no higher than 640 by 480 pixels. Entries at higher resolutions will be immediately disqualified. If necessary, use an image editing program to reduce the file size of your image before e-mailing it to us. Include the title of your photo along with a short description and how you photographed it. Don't forget to send your name, e-mail address, and postal address. Before entering, please read the full description of the contest rules and regulations.

This week's Hot Pic: "Keeping Up With the Jonses?," by Rose D. Richardson, Laguna Niguel, California

Rose says: "I simply had to take this somewhat eerie shot of the latest homes in the Batu Ferringhi Beach district of Penang, Malaysia. Prior to that day, I thought that such perfectly identical homes existed only on television and in the movies. I took the shot at midday, while standing on our hotel room terrace."