Optical attachment for reducing the focal length of an objective lens

摘要

An optical attachment having five or six elements and configured to be operably arranged on the image side of an objective lens to reduce the focal length and focal ratio of the objective lens is disclosed. The optical attachment is particularly suitable for adapting objective lenses designed with a relatively large working distance for a large format size to cameras having a smaller format size and relatively small permissible working distance. The optical attachments disclosed herein have high image quality at large aperture over a large field of view, and can be well-corrected for all major aberrations.

主权项

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 φG1, wherein −1<φG1/φ<−0.001, and including a most object-side-wise negative lens element that defines a most object-side-wise concave surface; 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