Mark Roberts wrote:
That's it: With K/M lenses the movement of the lever is directly
proportional to aperture diameter, with "A" and later lenses it's
directly proportional to aperture *area*.
If that's true then it is quadratic, not logarithmic, no?
Since the area varies with the square of the radius that'd be a "yes"
;-)
Define A = area of aperture; R = radius of aperture, D_A = displacement
of lever on A-series lenses and D_K = displacement of lever on K-series
lenses:
D_A prop A
D_K prop R
but
A prop R^2
so D_K prop sqrt(A)
ie the displacement of the lever on a K- (or M-) series lens is
proportional to the square root of the f-number.
S
