On Apr 20, 2005, at 10:46 AM, John Francis wrote:
Godfrey DiGiorgi mused:
. . . That means the 35mm lens on the DS is set to f/3.5 and the 50mm lens on the MX is set to f/5, roughly 1.5 stops different.
Check your math(s) - that's a difference of 1 stop, not 1.5 stops.
(Which is what you'd expect; the crop factor of the D/DS is 1.5, pretty close to the 1.414.. aperture ratio of a single f-stop)
I agree ... by the math, it's 1 stop. However, since the amount of sharpness in DoF is somewhat arbitrary, I feel that saying "1-1.5 stops" is close enough. For small prints, up to 4x6/5x7", you can get away with the 1.5 stop figure. For large prints in the 10x15 range, it's best to be conservative on DoF calculations.
Yeah yeah .. I just don't feel it's that cut and dry. DoF is a fuzzy business. ;-)
Godfrey
