It first helps to know what we’re comparing the magnification to in order to answer that question. Our eyes have a field of view and magnification roughly equal to a 50mm lens. So to find out the magnification factor of any lens, you simply divide the focal length of the lens you want to measure by 50. In this particular case, a 600mm lens has a magnification of 12 times because 600/50=12. Putting it another way, a 600mm lens magnifies what we typically can see with our unaided eyes by a factor of 12.