Patent ID: 8139293

Claim:
A projection lens with a variable effective focal length comprising, in the order from the screen-side to the SLM-side thereof, a negative lens group; and a positive lens group; wherein the projection lens satisfies the formulas of: −2<Φ1/Φ2<−0.5, −2<EFL1/EFL(W)<−1.5, 1.5<EFL2/EFL(W)<1.75, −1.2<EFL1/EFL(T)<−1, 0.8<EFL2/EFL(T)<1.2, 0.5<EFL(W)/BFL(W)<0.6, 0.68<EFL(T)/BFL(T)<0.75, 6.2<TTL(W)/EFL(W)<6.5, and 3.5<TTL(T)/EFL(T)<3.6; where Φ1 and Φ2 represent refractive powers of the negative lens group and the positive lens group respectively, EFL(W) and EFL(T) represent effective focal lengths of the projection lens when the projection lens is in the wide-angle state and in the telephoto state respectively, EFL1 and EFL2 represent effective focal lengths of the negative lens group and the positive lens group respectively, TTL(W) and TTL(T) represent overall lengths of the projection lens when the projection lens is in the wide-angle state and in the telephoto state respectively, and BFL(W) and BFL(T) represent rear focal lengths of the projection lens when the projection lens is in the wide-angle state and in the telephoto state respectively.