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Demystifying digital camera sensors once and for all

Jackie Dove | Oct. 11, 2013
Forget megapixels. A camera's soul is its sensor, and not all are created equal.

The soul of a digital camera is its sensor—to determine image size, resolution, low light performance, depth of field, dynamic range, lenses, and even the camera's physical size, the sensor is key.

An image sensor is a solid state device, the part of the camera's hardware that captures light and converts what you see through a viewfinder or LCD monitor into an image. Think of the sensor as the electronic equivalent of film. With film cameras, you could choose from hundreds of film brands, each with it own unique and identifiable characteristics. With digital cameras, much of that technology is built into the hardware, and special film-like effects are applied later with software.

Your camera's sensor determines how good your images look and how large they can be scaled or printed. Image quality depends on not only the size of the sensor, but also how many millions of pixels (light sensitive photosites) fit on it, and the size of those pixels.

The sensor size also affects what you see through the viewfinder—the relationship between what you're shooting and what actually gets recorded in the frame and passed through to your memory card. Smaller sensors apply a crop factor to lenses, capturing less of the scene than full frame sensors. The full frame reference point is always traditional 35mm film.

Confused yet? Don't be. Even if you don't know a CCD from a CMOS from a Four-Thirds from an APS-C, this guide breaks down that intimidating alphabet soup and walks you through the sensors you're likely to encounter.

Sensor types
The most common types of sensors are CCD (charged coupled device) and CMOS (complementary metal—oxide—semiconductor).

CCD is one of the oldest image capture technologies for digital cameras and has long offered superior image quality compared to CMOS sensors, with better dynamic range and noise control. While still prevalent in budget compact models, the CCD's basic construction and greater power consumption has caused it to be largely replaced by CMOS alternatives.

CMOS has been considered an inferior competitor to CCD, but today's CMOS sensors have been upgraded to match and even transcend the CCD standard. With more built-in functionality than CCDs, CMOS sensors work more efficiently, require less power, and perform better for high-speed burst modes.

The newer Foveon X3 sensor, based on CMOS technology, is used only in Sigma's compact cameras and DSLRs. Live MOS is a brand name for image sensors used by Leica, Panasonic, and Olympus in their Four Thirds System DSLRs manufactured since 2006. They reportedly offer CCD image quality with the lower power consumption of a CMOS.

Sensor sizes
Full Frame (36 x 24mm):The largest sensor size is called full frame, the same as a frame of 35mm film. Full frame sensors are almost twice as big as APS-C sensors, the next size down. Hefty pro-level beasts such as the Nikon D800, the Canon EOS 5D Mark III, and the Nikon D4 have full frame sensors. However, over the last year, smaller fixed lens cameras like the Sony Cyber-shot RX1 also feature full frame sensors. The Sony Alpha SLT-A99, a DSLR-like camera that has a fixed transluscent mirror as opposed to one that flips back to capture a shot, is also a full-frame model.


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