Title:
INNER FOCUS TYPE PHOTOGRAPHIC LENS
Document Type and Number:
Japanese Patent JPH01154111
Kind Code:
A
Abstract:
PURPOSE:To obtain the photographic lens which has high optical performance, a large aperture ratio, and a relatively wide field angle by constituting three lens groups which meet specific requirements and moving a 2nd group on the optical axis for focusing. CONSTITUTION:The lens 1A which is closest in the image plane side in a 1st group I has its concave surface on the image surface side and the lens 3a which is closest to the object side in a 3rd group III has its concave surface on the object side. Then an inequality I holds, where R1A is the radius of curvature of the lens surface of the lens 1A on the object side, N3A the refracting index of its material, R3A the radius of curvature of the lens surface of the lens 3A on the image plane side, N3A the refractive index of its material, f2 the focal length of a 2nd group II, and (f) the focal length of the whole system. Then when focusing is performed by moving the 2nd group II, aberrational variation is reduced. Consequently, the aberrational variation at the time of focusing with a large aperture ratio and an about 30 deg. photographic field angle is small and high optical performance is obtained over a wide photographic distance range.
Inventors:
ENDO HIROSHI
Application Number:
JP31390087A
Publication Date:
June 16, 1989
Filing Date:
December 11, 1987
Export Citation:
Assignee:
CANON KK
International Classes:
G02B9/64; G02B13/18; (IPC1-7): G02B9/64; G02B13/18
Attorney, Agent or Firm:
Takanashi Yukio