Feature: Digital Zoom's Ugly Little Secret

After the number of megapixels, zoom is without a doubt the spec that defines the power of a digital camera. People compare zoom ratings like some guys chat about cars. Conversations typically go something like this:

"What's the zoom on that baby?"

"3X optical, 2X digital."

"Not bad, but I've got a 4X optical, 3X digital under the hood of this little guy. I can shoot the wing of a butterfly at 400 yards."

"Nice."

Digital Isn't Always Better

But even though the digital zoom rating is a common benchmark that buyers use for choosing a camera, it may not deliver the results you expect.

As you probably know, virtually all digital cameras have both an optical and a digital zoom. The camera's optical zoom increases the magnification of a scene by changing the relationship of optical elements in the lens. It zooms in or out while maintaining a sharp, high-quality image at the camera's full pixel resolution. But digital zooms work on a completely different principle.

A digital zoom enlarges the image simply by "cropping" it. As you zoom in on a scene, the camera draws a crop box around the pixels in the image sensor and discards information outside the frame. Only the pixels inside the frame are recorded. And that means that the sensor's full resolution isn't being used. The more you zoom in, the fewer pixels you'll have in your final image. That's a real waste of your camera, because you're throwing away image quality.

With all that in mind, there's no reason to let a digital zoom rating play into your buying decision.

Bottom Line: Avoid Using the Digital Zoom

I give simple advice to everyone who has a digital camera: Never use the digital zoom feature. Ever. Why bother? You can crop the scene just as well in an image editor on your PC. In fact, if it's possible, disable the digital zoom entirely. That way it can't be kicked in by accident and spoil a shot. Most cameras allow you to turn off the digital zoom somewhere in the camera's menu system. Look for a setting in the menu called Digital Zoom, and set it to No or Off.

What if you can't disable the digital zoom? How can you tell when the optical zoom ends and the digital zoom kicks in? In most cameras, the viewfinder displays a gauge while you're zooming so you can tell where you are within the camera's zoom range. Often, there's a subtle detent in the gauge that indicates the transition from optical zoom to digital. As you press the zoom button, the zoom will pause momentarily at the end of the optical range--at the detent in the gauge--before resuming the zoom into digital. When you see the zoom status bar reach the digital detent, take your finger off the zoom button. Consider the digital zoom range off limits.

Do-It-Yourself Digital Zoom

As I mentioned, remember that you can "zoom in" on your pictures after they're on your PC--just use your image editor's Crop tool to hone in on the part of the image that most interests you. Here's where high-megapixel cameras really pay for themselves. If you have a 3-megapixel model, for instance, you can't afford to crop it very much if you want to make an 8-by-10-inch print. But a 6- or 8- megapixel camera has pixels to spare. You can crop away half the picture and still have plenty of resolution to make a sharp, snappy print.

And while no software can ever add information to a picture that wasn't there to begin with, there are some programs that can help you get good-quality prints from lower-resolution images.

For example, you might want to try Pxl SmartScale from Extensis. Pxl SmartScale is a powerful image scaling program that can preserve quality when you make large prints from images that might not ordinarily have enough pixels to print well. I use it frequently, and I find it does an impressive job of retaining overall sharpness when I need to crop a picture to "zoom in" for a better composition. I've found the program for less than $200 at the PC World Product Finder.