function f = sing2(v); % % f(1) is power error % f(2) is coma % f(3) is spherical aberration global cv th rn; cv(2)=v(1); % first surface curvature cv(3)=v(2); % second surface curvature yap = 5.0; uco = 0.1; scl = yap^2/2; ya = parax([yap 0],cv,th,rn); yc = parax([0 uco],cv,th,rn); f(1) = -ya(4,2)/ya(1,1) - 1/20; % power error w = ford(ya,yc,cv,th,rn,1); f(2) = w(2)/scl; f(3) = w(1)/scl; f = f';