Optical system, finder optical system, relay type finder optical system, eyepiece optical system, and single-lens reflex camera

Abstract

The invention concerns an optical system adapted to split an optical path from a taking optical system into a finder optical system, which has a camera-shake correction function best suited for the finder optical system, and so on. This optical system comprises a taking optical system and a finder optical system. The taking optical system comprises an optical path splitter means operable to split an optical path into the finder optical system, and the finder optical system includes a relay optical system RLS for re-forming a subject image once. Anti-shake is implemented by shifting an optical subsystem RL that forms a part of the finder optical system in a plane vertical to an optical axis.

1 . An eyepiece optical system, comprising, in order from a side of an image being viewed,
 a first lens having negative refracting power,   a second lens having positive refracting power,   a third lens having positive refracting power, and   a fourth lens having positive refracting power,   
     wherein the eyepiece optical system satisfies the following condition:
   2.5 ≦f 123 /fA ≦8  (4-1) 
 
     where f123 is a composite focal length of the first lens, the second lens and the third lens, and
 fA is a focal length of the eyepiece optical system. 
 
   
   
       2 . An eyepiece optical system, comprising, in order from a side of an image being viewed,
 a first lens having negative refracting power,   a second lens having positive refracting power,   a third lens having positive refracting power, and   a fourth lens having positive refracting power,   
     wherein the eyepiece optical system satisfies the following condition:
   1 ≦f 4 /fA ≦2  (4-2) 
 
     where f4 is a focal length of the fourth lens, and
 fA is a focal length of the eyepiece optical system. 
 
   
   
       3 . An eyepiece optical system, comprising, in order from a side of an image being viewed,
 a first lens having negative refracting power,   a second lens having positive refracting power,   a third lens having positive refracting power, and   a fourth lens having positive refracting power,   
     wherein the eyepiece optical system satisfies the following condition:
   0.02 ≦d 4 /fA ≦0.2  (4-3) 
 
     where d4 is an axial thickness of the fourth lens, and
 fA is a focal length of the eyepiece optical system. 
 
   
   
       4 . The eyepiece optical system according to  claim 1 , wherein the image being viewed is an image or aerial image formed through an image-formation lens. 
   
   
       5 . A relay type finder optical system, comprising:
 a relay optical system operable to re-form a primary image formed through a taking optical system, and   an eyepiece optical system operable to view an image re-formed through the relay optical system, wherein:   the eyepiece optical system is the eyepiece optical system according to  claim 1 .   
   
   
       6 . The relay type finder optical system according to  claim 1 , wherein:
 the fourth lens remains fixed, and diopter control is implemented by integral movement of the first lens, the second lens and the third lens in an optical axis direction.   
   
   
       7 . The eyepiece optical system according to  claim 1 , wherein the first lens and the second lens are mutually cemented into a cemented doublet. 
   
   
       8 . The eyepiece optical system according to  claim 1 , wherein the first lens and the second lens are mutually cemented together into a cemented doublet. 
   
   
       9 . The relay type finder optical system according to  claim 6 , which satisfies the following conditions:
   2.5 ≦f 123 /fA ≦6.5  (4-1)′     1.4 ≦f 4 /fA ≦2  (4-2)′   
     where f123 is a composite focal length of the first lens, the second lens and the third lens,
 f4 is a focal length of the fourth lens, and 
 fA is a focal length of the eyepiece optical system. 
 
   
   
       10 . An imaging apparatus, comprising:
 a taking lens,   a quick return mirror adapted to reflect light rays leaving the taking lens,   an imaging device operating such that when said quick return mirror is retracted, an image formed by light rays entering from the taking lens is converted into electrical signals, and   an eyepiece optical system as recited in  claim 1 , on which light rays reflected off said quick return mirror are incident.