On Sun, Jul 17, 2005 at 06:50:17AM -0700, Godfrey DiGiorgi wrote: > Perhaps you're seeing evidence of the fact that the "1.5x crop > factor" is a simple *linear* approximation of the field of view > difference. Field of View in fact does not change linearly with > respect to focal length on a format, a true factor for an 18mm lens > is probably a little closer to 1.4-1.3x to give a 100% accurate > calculation. I'll make up a chart demonstrating this for you in a > little bit.
... and you'll find the factor is 1.5, not 1.4 or 1.3x. True, angle of view doesn't change linearly with focal length, or crop factor, or whatever. But if you reduce the (linear) width of the sensor by the 1.5 crop factor, you need to reduce the focal length by exactly that same factor of 1.5 to maintain the same angle of view.
