function drawsys(ap,th,cv,lp)
% DRAWSYS(AP,TH,CV,LP)
%
% draws a lens system
%
% AP aperture height
% TH thickness
% CV curvature
% LP index of first surface of each lens

ts = cumsum(th);
for k=lp
    drawlens(ap(k),th(k),cv(k:k+1),ts(k-1));
    hold on;
end
axis equal;
hold off;
clear k ts;