On Jul 17, 2005, at 2:06 PM, John Francis 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.
How do you explain the difference in the results from comparing the
angle of views as I did with Rui's FoV calculator, John? Just round
off error? There seems to be a predictable pattern to the error.
Godfrey
