function B2 = B2calc(p, AF)
%B2calc(p, AF)	Calculates B2, an essential constant in determining how 
% 	the pointspread function is effected by pupil size. Input variables 
%	are as follows:
% 
%p = pupil size in mm
%AF = age factor (calculated with agefact)
%
%Output value is in c/rad^-1

d = 3.2; % defining constant d

B2 = ((1 + ((d/p)^2)) * ecalc(AF) - 1/(bcalc(AF) * p)); %actual equation