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Giz Explains: Digital Camera Image Sensors

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Spring is the primetime for new cameras, hence the cheap cam battlemodo, an entry-level DSLR battlemodo, not to mention loads of rumors and breakthroughs. It's a lot to keep up with, and you may not even know what's going on with the camera in your pocket. If that's the case, don't worry, here's a quick primer an digital camera image sensors—just what you need to know.


There are two major types of image sensors for digital cameras and camcorders: CCD (charged-couple device) and CMOS (complementary metal-oxide-semiconductor, sometimes also known as active pixel sensor). We're not going to get into the really geeky differences, because you don't really need to know or care. What you should know is that higher-end digital SLRs (the big cameras with a removable lens) use CMOS because it's easier to make bigger CMOS sensors; and mobile phones do because CMOS uses less power. That said, most point-and-shoot cameras and most camcorders use the more common CCD sensor.

The big thing about image sensors? Size matters. And we're not talking megapixels. Half the reason shots taken with a DSLR look so much better than the ones taken with your backpocket point and shoot is that the DSLR's image sensor is massive in comparison. The difference can be even more stark when you compare shots from a 2-megapixel cameraphone with a standard 2-megapixel camera. (The other half is the lens—pros will tell you it's all about the glass—but we're talking sensors here.)


You see, in order to cram more and more pixels onto tiny sensors—think $150 cameras claiming to rock 10 megapixels of awesome—you've gotta make the pixels smaller and smaller, which a) makes photos look grainy and b) makes the sensor suck at picking up light. The result: Low-light shots look like they're off a security camera from 1997, especially when you crank up the ISO (light sensitivity) setting. When a point-and-shoot promises you shots at 1600 ISO, it's generally a sacrifice you don't want to make: unuseable pics full of rainbow-colored noise.

The best DSLRs use 35mm sensors, that is, a sensor that is the same size as a frame of standard film. This is known as "full frame." The D3, Nikon's biggest, baddest DSLR camera, costs $5,000 but only shoots at 12.2 megapixels. By contrast, its Canon competitor rocks 23. Still, the D3 beats all comers in low-light shooting, mainly because its 36 x 23.9mm sensor doesn't try to shove a bunch of megapixels onto it. By better, we mean that the pictures have less noise (that rainbow-colored grain). It's also why rumors of a new 24.4-megapixel Nikon spark some concern—there's no way it'll shoot as well in the dark. Sony promises to release a 25-megapixel Alpha DSLR this September. It will be sweet, but being the highest in megapixels doesn't guarantee its place in the winner's circle.

So when you're out camera shopping, don't think that more megapixels is more better. A lot of review sites will list the size of a camera's image sensor (plus the other stuff obviously) and a 6MP camera with a sensor the same size as an 8MP model is gonna take better pictures. Check out these two Kodak point and shoots from CES, the m1033 and Z1085. Same megapixel count, but the Z1085 has a bigger sensor (1/1.7-inches is larger than 1/2.3-inches, non-math majors) and will almost certainly shoot less noisy pictures.


Of course, a DSLR will take better shots than any point-and-shoot, but while DSLRs are getting cheaper every day (only $475 for a Nikon D40 or $450 for a Canon Digital Rebel XT (both with lens) that might not fit everyone's budget. Plus, they don't fit in your pocket, like your dumb cameraphone.


Something we missed, or you still wanna know? Send any questions about cameras (or anything else) to, with "Giz Explains" in the subject line.