Hi. As you guys know, an object-telecentric system (a system with constant magnification) has per definition an entrance pupil that is infinitely far away. One can construct such a system by taking a lens and placing an aperture stop (AS) at its focal point. My issue is that I am struggling to ray-trace the aperture stop (AS) through the telecentric system. I just can't get the "infinitely far away entrance pupil" condition without also assuming that the aperture stop has a diameter approaching zero. I am assuming paraxial approximation and geometrical optics. Is perhaps this the reason behind my difficulties?