Projection lens and projection-type display apparatus using the lens

A projection lens which is telecentric on a reduction side, which enlarges and projects images formed on a conjugation surface on the reduction side onto a conjugation surface on a magnification side, comprising only:

• a first lens having a positive power and at least one surface that is an aspheric surface;
• a second lens having a negative power and having a concave surface on the magnification side;
• a third lens having a positive power and having a convex surface on the reduction side;
• and
• a fourth lens having a positive power, which are arranged in order from the magnification side,
• wherein the following formulas (A), (B), (C), and (D) are simultaneously satisfied:
• 0.8<Bf/f (A);
• 1.1<f1/f<1.6 (B);
• Nd1<1.7 (C);
• and
• vd1<35 (D), where
• Bf:
• air conversion back focus on the reduction side
• f:
• focal length of the entire lens system
• f1:
• focal length of the first lens
• Nd1:
• refractive index of the first lens, and
• vd1:
• Abbe number of the first lens.