Celestron wrote in post #14934462
Very nice image . However the 7D is a 1.6x crop camera so that gives you 1920mm .
600mm X 1.6 crop x 2xII = 1920mm or 600mm x 2xII x 1.6 crop =1920mm . Reguardless how you figure this is what you get mm figures . FF starts with the 5DII . Anything before that is a 1.6x crop (APS-C size) camera .
The 7D, and other crop cameras (1.6x, 1.3x, etc) do not change the focal length. I understand what you're trying to get at though...if you want to fill the frame similarly with a FF camera, then you'd need 1920mm. It's a "FF equivalent" focal length.
If you were to crop the borders of a FF image to the size of a 1.6 crop sensor the image would be the same as the crop's(smaller resolution, but otherwise the same using the same setup (lens, settings, position, etc)). Since cropping a FF image can get you the same image of a 1.6x crop camera, does that mean the focal length changes when you crop? See? It doesn't right?
Sorry, I just wanted to clarify that.