The authors address a large gravitational lens, of dimensions comparable with observer-lens-source distances, for arbitrary lens-observer-source angles. The lens is approximated by a small, pressureless, spherically symmetric perturbation in an Einstein-de Sitter universe. The deflection angle contains essential terms which do not appear when the lens is approximated by an isolated body in a Minkowskian space. These terms should be considered to study the optical appearance of the inhomogeneity. The lens equation explicitly conserves brightness over the whole celestial sphere of the observer.