An exemplary projection lens includes, in this order from the magnification side to the minification side thereof, a negative lens group having negative fraction of power, and a positive lens group having positive fraction of power. The positive and negative lens groups each include a number of positive and negative lenses. The focal length of the projection lens is adjustable. The projection lens satisfies the formulas of: −2 56, where F1, and F2 respectively represent the effective focal lengths of the negative lens group and the positive lens group, Fw is the shortest effective focal length of the projection lens, and Vg2 is the average of the Abbe number of the positive lenses in the positive lens group.