Patent ID: 6014267
Filing Date: 2000-01-11
Classification: G02B

Abstract:
A variable magnification optical system comprising, from a projection side:a first lens unit having a negative optical power and including at least one lens element having an aspherical surface, the first lens unit moving along an optical axis direction during zooming operation;a second lens unit having a positive optical power, the second lens unit moving along an optical axis direction during the zooming operation; anda third lens unit having a positive optical power, including at least one lens element having an aspherical surface and including a positive lens element,wherein the following conditions are fulfilled:0<.DELTA.X1/fW<0.08-0.04<.DELTA.X3/fW<00.015<.THETA.3-(0.644-0.00168.multidot..nu.d3)<0.0665<.nu.d3<100where.DELTA.X1 represents an aspherical deviation of the lens element having an aspherical surface in the first lens unit;.DELTA.X3 represents an aspherical deviation of the lens element having an aspherical surface in the third lens unit;fW represents a focal length of the optical system in its entirety in a shortest focal length condition;.THETA.3=(ng3-nF3)/(nF3-nC3).nu.3d=(nd3-1)/(nF3-nC3)ng3 represents a refractive index of the positive lens element in the third lens unit for g-line (435.84 nm);nF3 represents a refractive index of the positive lens element in the third lens unit for F-line (486.13 nm);nd3 represents a refractive index of the positive lens element in the third lens unit for d-line (587.56 nm); andnC3 represents a refractive index of the positive lens element in the third lens unit for C-line (656.28 nm).