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Patent Searching and Data


Title:
IMAGING OPTICAL SYSTEM, CAMERA AND PERSONAL DIGITAL ASSISTANT
Document Type and Number:
Japanese Patent JP2011048026
Kind Code:
A
Abstract:

To provide an imaging optical system which has a large diameter lens and a small F-number, has preferable imaging performance and can effectively reduce the generation of a ghost by the use of an ND filter.

The imaging optical system includes: an aperture stop S; a first lens group G1 arranged on the object side of the aperture stop S; a second lens group G2 arranged on the image side; and a parallel plate-like ND filter ND arranged on approximately the same position as the position of the aperture stop S in the optical axis direction of the first and second lens groups, wherein the second group G2 includes positive refractive power as a whole, the ND filter ND is retractable from the optical axis and can attenuate a light amount, and if an average reflectance in the wavelength region of light from 400 nm to 700 nm is R1 with respect to the incident light from the object side and is R2 with respect to the incident light from the image side, R1 and R2 satisfy the condition (1): (1) R1/R2>2.0.


Inventors:
Nakayama, Takahiro
Sudo, Yoshifumi
Application Number:
JP2009000194668
Publication Date:
March 10, 2011
Filing Date:
August 25, 2009
Export Citation:
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Assignee:
RICOH CO LTD
International Classes:
G02B13/04; G02B5/00; G02B7/02; G02B13/18; G03B9/02; G03B11/00