When I first learned about the crop factor, I was all like “what does it matter? Just back up.” Seemed too simple to me. Then in real life situations you understand why many photographers like to shoot “Full Frame”.
Most DSLR cameras do not shoot full frame, that is 35 mm. The camera has a crop factor which is determined by the dimensions of the camera’s image sensor. Smaller sensors = more cropping.
Both my Canon Rebel XT & 7D have a crop factor of 1.6. If you compare images shot full frame this is what you would get:
You can think of it like this: a camera with a crop factor magnifies your lens. If you have a 50mm lens (nifty fifty, anyone?) and your camera has a crop factor of 1.6 then you’re essentially shooting with an 80mm focal length (50mm x 1.6 crop factor).
In tight spaces like in someone’s home or a small studio, this can present problems. You may not be able to include certain elements in a photo if you don’t have space to back up.
On the other hand some people like shooting with a zoomed in view because you get a close up picture without cropping, preserving the full megapixel potential of your sensor. When you crop an image you lose quality.
Point & shoot cameras can have a crop factor as large as 6.
Canon’s full frame cameras are the 5D & 5D mark 2 and the 1DS mark 2 & 1DS mark 3. The other Canon SLRs have a crop factor of 1.3, 1.5 or 1.6.