Image sensors come in a range of sizes, as you can see in this helpful diagram from Wikipedia. A bigger sensor, like the full-frame slab used in the Canon 5D or Nikon D3, has more space for photosites than the thumbnail-sized sensor that fits in little point-and-shoots. So, if they’re both 12-megapixels, that is, they both have 12 million photosites, the bigger sensor can obviously collect a lot more light per pixel, since the pixels are bigger.
If you’re grasping for a specification to look for, the distance between photosites is referred to as pixel pitch, which roughly tells you how big the photosite, or pixel, is. For instance, a Nikon D3 with a 36mm x 23.9mm sensor has a pixel pitch of 8.45 microns, while a Canon S90 point-and-shoot with a 7.60 mm x 5.70 mm sensor has a pitch of 2 microns. To put that in less math-y terms, if you got the same amount of light to hit the image sensors the D3 and the S90—you know, you took the exact same exposure—the bigger pixels in the D3 would be able to collect and hold on to more of the light. When you’re looking for low-light performance, it’s immediately obvious why that’s a good thing.
February 28th, 2010 at 3:58 pm
I went to that website to read the full article. it was very informative. But some of the people who made comments did not understand the logic of it all. with D-SLR camera having the ability to capture at a ISO of 102.400 and still have a usable photo. I read and article I think was in Digital Pro or SHutterbug when they compared the Canon new camera the 1D Mark IV and the Nikon D3s. the Canon is an APS-H (1.3x) and is 16.1 Megapixels Vs Nikon Full frame 12.1 Megapixels. As you know Jim, I am a very avid reader of Photography Books and Magazines. I feel that the Nikon’s noise reduction Algorithms in their CPU does a far better job. A smaller pixel size is one other way to improve the StoN ratio’s, even though Nikon D3s has a pixel size of 8.45 microns and Canon has 5.7 microns, the Canon has about 4 megapixel more then the Nikon. For a sensor with more pixels you think it could get their firmware to do a better job. also you should add http://www.Shutterbug.com and Digital Photo Pro http://www.digitalphotopro.com to your list. You can spend hours surfing on their sites. A very large Database of information on everything Photography.
Kristyanna