Patent ID: 8937773
Filing Date: 2015-01-20
Classification: G02B

Abstract:
1. A projection lens that projects image information displayed on the reduction side conjugate position onto the magnification side conjugate position, the projection lens comprising an aspherical lens having a positive refractive power that simultaneously satisfies conditional expressions (1) to (5) given below, and satisfying conditional expressions (6) and (7) given below: where: hfa is the maximum height of axial ray on the magnification side surface of the aspherical lens; hfb is the height of principal ray on the magnification side surface of the aspherical lens at the maximum angle of view; hra is the maximum height of axial ray on the reduction side surface of the aspherical lens; hrb is the height of principal ray on the reduction side surface of the aspherical lens at the maximum angle of view; Xf (y) is the difference in an optical axis direction between the magnification side surface of the aspherical lens and its paraxial spherical surface at a height y; Xr (y) is the difference in an optical axis direction between the reduction side surface of the aspherical lens and its paraxial spherical surface at a height y; NdA is the refractive index of the aspherical lens at the d-line; νdA is the d-line based Abbe number; Bf is the back focus of the entire system when the reduction side is taken as the back side; f is the focal length of the entire system; Imφ is the maximum effective image circle diameter on the reduction side; and dexp is the distance from the reduction side conjugate position to the reduction side pupil position, in which y is the height from the optical axis and is any arbitrary value within a range of 0.5≦y≦1 when the smaller one of the hfa and hra is taken as 1; and the sign of Xf(y) and Xr(y) is positive if each surface of the aspherical lens is on the reduction side of its paraxial spherical surface and negative if it is on the magnification side.