Sun, Dec 26, 2010 - Page 11 News List

Small cameras with big sensors and how to compare them

By David Pogue  /  NY Times News Service, NEW YORK

This is two columns in one. One is about new pocket cameras that take sharp pictures in low light without the flash — a magnificent moment in the evolution of cameras, thanks to an unusually large light-sensing chip.

The other column is about a shady scheme that’s being perpetuated by the world’s camera companies.

If there’s one single statistic that you can use to compare cameras, it’s sensor size. A bigger sensor soaks up more light. You get better color and sharper images, especially in low light. A big sensor generally means better color and clarity, and less grain and blur in low light. Digital single-lens reflex (SLR) cameras have enormous sensors, which is why professionals use them. (Of course, SLRs are also enormous and heavy.)

However, when you’re shopping, how do you find out the sensor size? It’s not on the box. It’s not in the ad. You can Google it (“Rebel XT sensor size,” for example). However, the information you will find is mostly worthless.

First, sensor sizes for SLRs are expressed in millimeters, width by height (23.7mm x 15.6mm), not inches diagonal. Yet sensor sizes for pocket cameras are expressed differently, believe it or not, as ratios, like “1/2.3 inches.” You can’t easily compare SLR sensors with pocket camera sensors and you can’t compare pocket cameras without a calculator.

At sensor-size.com, you can convert every sensor format into inches diagonal. However, recently, I learned something scary: Even that isn’t the nastiest part of the sensor-size shenanigans.

It turns out that even if you divide out the “1/2.3 inches” thing, the result — 0.435 inches, for example — does not represent the sensor’s real size. Those decimal fractions don’t measure the sensor. Instead, because of a bizarre 50-year-old convention, they measure the 1950s television tube that those rectangular sensor chips could fit inside of. And that’s the outside diameter.

In other words, the actual sensor size is much smaller than what the camera companies publish — about one-third smaller. A camera with a 1/2.7-inch chip does not measure 0.37 inches diagonal — 0.38 is the size of the tube it would fill. The actual sensor is much smaller: 0.26 inches. (The full explanation is here: www.bit.ly/fQw37l. I confirmed the information with Canon.)

This might sound awfully picky, but it’s not. It’s like finding out that the TV industry has been exaggerating its screen size for 50 years.

The camera companies say that they use this absurd measurement not to fool you, but out of many decades of habit. Well, it’s time to change.

In the early digital camera days, every company measured battery life differently. Finally, the Camera and Imaging Products Association (CIPA, the Japanese camera trade group) proposed a standard, realistic testing protocol. Today, shots-per-charge is measured identically by every brand, and you can rely on that figure. Well, guess what? For its next trick, CIPA should clean up this sensor-size mess and soon.

For now, you can use those decimal fractions only for comparison purposes. A 1/1.7-inch sensor is definitely bigger than a 1/2.8-inch sensor, even though those aren’t the real measurements.

What the world has always wanted is a big sensor in a small camera, so you can get sharp photos in low light without hauling around an SLR. This year, the camera industry took a big step toward that glorious future. Canon’s PowerShot S95 (US$370), Panasonic’s Lumix DMC-LX5 (US$400) and Samsung’s TL500 (US$370) are all pocket-size cameras with sensors at least 50 percent larger than other pocket cameras.

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