Canon Cameras like the Rebel Series or the 10D-50D series have a crop factor of 1.6 when compared to 35mm film. That means the sensor is smaller than a 35mm frame. So when you take a picture, it is like cropping it by a factor of 1.6. You still have all those pixels of 15.1 or whatever it is.
If you took a picture with a 5D Mark 2 and a 300mm lens, that would be the standard, because the 5D2 is full frame - or uncropped. But if you took that same picture with a 50D and a 300mm lens, it would look almost the same as if you had taken that 5D picture and cropped it in by a factor of 1.6.
So for sports photographers or wildlife photographers where you want more 'reach' the crop factor is a good thing. For landscape or wedding photographers where you don't need that reach, it is not as good a thing.
Nikon cameras are 1.5x crop up to the D300. The D700 and D3 series cameras are full frame.
Canon's 1Dmark3 is a 1.3x crop, while the 5D series and the 1Dsmark3 are full frame. The Rebel and Prosumer lines are 1.6x crop.
If you took a picture with a 5D Mark 2 and a 300mm lens, that would be the standard, because the 5D2 is full frame - or uncropped. But if you took that same picture with a 50D and a 300mm lens, it would look almost the same as if you had taken that 5D picture and cropped it in by a factor of 1.6.
So for sports photographers or wildlife photographers where you want more 'reach' the crop factor is a good thing. For landscape or wedding photographers where you don't need that reach, it is not as good a thing.
Nikon cameras are 1.5x crop up to the D300. The D700 and D3 series cameras are full frame.
Canon's 1Dmark3 is a 1.3x crop, while the 5D series and the 1Dsmark3 are full frame. The Rebel and Prosumer lines are 1.6x crop.
