Patent ID: 8903232
Filing Date: 2014-12-02
Classification: G02B,G03B

Abstract:
1. A focal reducing attachment having an object side, an image side, an optical power φ, a magnification M, and comprising: a total of five or six lens elements arranged in four lens groups G1, G2, G3 and G4 in order from the object side to the image side, and wherein: a) lens group G1 has an optical power φ b) lens group G2 has positive power and has a positive lens element with a most object-side facing surface having a curvature CvOb2; c) lens group G3 having negative power and having a negative lens element with a most image-side-facing surface having a curvature CvIm3; d) a positive powered lens group G4; and wherein 2<(CvOb2+CvIm3)/φ<30 and 0.3<M<1.0.