Originally posted by Jed
Oooh Tweek.... me confused now.
Zoom factor refers to the number of times a lens is able to "zoom", but this is completely dependent on the base focal length of a zoom. Hence, a 50-500mm lens is a 10x zoom lens. A 28-300mm lens is a 10.7x zoom lens, even though it only has 272mm of "zoom" compared to the 450mm for the former lens.
Yup in my argument I was referring to the same base focal length, in the case of 1X zoom vs 2X zoom. Sorry for not making that clear.
Every doubling of focal length results in a halving of the angle of view. So a 20mm lens has double the angle of view of a 40mmm lens, which has double that of an 80mm lens and so on. This is measured as a diagonal.