function B3 = B3calc(AF, m)
%B3calc(AF, m)	Calculates B3, an essential constant in determining how 
% 	the pointspread function is effected by eye pigmentation. Input variables 
%	are as follows:
%
%AF = age factor (calculated with agefact)
%m = pigmentation factor.
%
%Note that this function can be used with the pigment function to obtain a 
%default m value.
%Usage: B3calc(AF, pigment);
%
%(From Ijspeert, et al. 1992.)

B3 = (10+ 60*m - 5/AF)^-1; %equation