The present invention relates generally to an eyepiece optical system adapted to enlarge an object to view it with the naked eye. More specifically, the invention relates to an electronic view finder adapted to enlarge an image shown on a display plane of an image display apparatus to view it with the naked eye.
Among eyepiece optical systems used so far with cameras (such as video cameras, single-lens reflex cameras, and digital cameras), there has been an eyepiece optical system of the type known that is made up of three lenses: a positive lens, a negative lens and a positive lens in order from an object (display plane) side toward an exit (exit pupil) side, as disclosed in Patent Publications 1, 2 and 3.
The eyepiece optical system of the triplet type having such a positive-negative-positive refractive power profile works in favor of achieving higher performance, because they can easily be corrected for aberrations such as spherical aberrations, albeit comprising fewer lenses. Eyepiece optical systems of other types have also been known from Patent Publications 4 to 9.    Patent Publication 1: JP(A) 2007-264179    Patent Publication 2: JP(A) 2002-082290    Patent Publication 3: JP(A) 2004-258653    Patent Publication 4: JP(A) 2008-107380    Patent Publication 5: JP(A) 2008-203290    Patent Publication 6: JP(A) 2002-365562    Patent Publication 7: JP(A) 2007-225835    Patent Publication 8: JP(A) 2001-272610    Patent Publication 9: JP(A) 2002-048985
However, the eyepiece optical system of Patent Publication 1 is found to be insufficient in terms of optical performance; for instance, when the viewer s pupil is away from the optical axis, there is less insignificant distortion of the image being viewed.
The eyepiece optical systems of Patent Publications 2 and 3 are longer in terms of the whole focal length, working against achieving size reductions of the whole optical system including a display plane and making sure the angle of field.
In view of the foregoing problems, the first aspect of the invention has for its object the provision of an eyepiece optical system that albeit being of smaller size, works in favor of making sure the angle of field and optical performance, and an electronic view finder incorporating the same.
The second aspect of the invention has for its object the provision of an electronic view finder that includes a first lens group and a rear-side lens group on an exit side with respect to the first lens group and is of the type that focusing is implemented by moving the rear-side lens group, wherein there is an eyepiece optical system used that works in favor of offering a sensible tradeoff between size reductions and optical performance.