Digicams: It's all about the sensor size

A 12-megapixel camera is better than a 10-megapixel camera... right?

Megapixel madness has cooled off in recent years, but the question and the confusion are still out there: How many megapixels are enough? And it can't hurt if I get a few million more, can it?

This insightful post at the Christian Science Monitor offers a counterintuitive answer to the latter question, suggesting that, yes, squeezing too many megapixels into a tiny camera can actually leave you with a lesser quality image than you'd get with a lower-megapixel one of the same physical size.

The problem is the size of the CCD sensor, the chip inside the camera which actually captures the image when it's exposed to light and which then converts it into a digital file.

The problem is that a CCD sensor has to be kept very small in order to keep the size of the camera that contains it to a reasonable size. Pocket cameras about the size of your wallet are now the norm, so unless you want to upgrade to a bigger, bulkier model, there's only so big a CCD can get. (And bigger CCDs also cost more, of course.)

In order to raise the number of megapixels the camera is rated for, manufacturers can cram more resolution into that sensor. This is easier said than done, and the result is often that images may be larger in size, but lower in quality, as, says the piece, "the overburdened sensor can lose sharpness, struggle in low-light situations, and add 'noise' (small blotches or odd colors)."

How can you arm yourself informationally when shopping for a camera? First, sensor size may not be on the front of the box, but it is usually available in the fine print, especially if you look for information about the camera online. The catch is that sensor size is described in a very bizarre way: Many pocket cameras have a 1/2.5" sensor, which is smaller than the less commonly available but "better" 1/1.7" sensor. Scroll down on this page to the section on Sensor Size and you'll find a list of common sensor size names and the actual overall height and width of that sensor. In the case of sensor size, bigger is always going to be better.

And of course, you don't need as many megapixels as you think. The size of physical prints you'd ultimately like to make is the key for most users. This calculator will let you do the math the easy way: An 8.0-megapixel camera will let you print at 300dpi a photo that's over 8x10 inches in size without losing any clarity from the photo. Even a garden-variety 5-megapixel camera can print a 5x8" print at 300dpi with no trouble. But 10, 12 megapixels? You simply aren't likely to ever need that much.