Finder optical system and image pickup apparatus using the same

A finder optical system comprising, in order from an object side thereof:

• an objective optical system having a positive refracting power;
• an image-inverting optical system for erecting an intermediate image formed by said objective optical system;
• and
• an ocular optical system having a positive refracting power;
• wherein said objective optical system includes:
• an optical system having at least two movable units moving when zooming is performed, said optical system having a positive composite power;
• and
• a prism placed on a pupil side of said optical system, said prism including an image-inverting function, and said prism including at least one reflecting surface having a rotationally asymmetric surface configuration;
• wherein:
• at least either one of a first transmitting surface and first reflecting surface of said prism has a negative power, and a second transmitting surface of said prism has a positive power, and
• a composite focal length of said at least two movable units satisfies the following condition:
• 0.3<fmove/fW<0.9 (7)
• where fmove is the composite focal length of said at least two movable units at a wide-angle end, and fW is a focal length of said objective optical system at the wide-angle end.

A finder optical system comprising, in order from an object side thereof:

• an objective optical system having a positive refracting power;
• an image-inverting optical system for erecting an intermediate image formed by said objective optical system;
• and
• an ocular optical system having a positive refracting power;
• wherein said objective optical system has:
• at least two movable units moving when zooming is performed;
• and
• a prism placed on an object side of the intermediate image formed by said objective optical system, said prism having three reflecting surfaces, wherein at least one of said reflecting surfaces has a rotationally asymmetric surface configuration, and
• wherein a composite focal length of said at least two movable units satisfies the following condition:
• 0.3<fmove/fW<0.9 (13)
• where fmove is the composite focal length of said at least two movable units at a wide-angle end, and fW is a focal length of said objective optical system at the wide-angle end.

A finder optical system comprising, in order from an object side thereof:

• an objective optical system having a positive refracting power;
• an image-inverting optical system for erecting an intermediate image formed by said objective optical system;
• and
• an ocular optical system having a positive refracting power;
• wherein said objective optical system includes, in order from an object side thereof:
• a negative first unit;
• a positive second unit;
• and
• a negative third unit;
• wherein at least the first unit and the second unit are movable units moving when zooming is performed, and the third unit is formed from a prism including an image-inverting function, said prism including an entrance surface having a negative refracting power and at least one reflecting surface having a rotationally asymmetric surface configuration with a negative power.

A finder optical system comprising, in order from an object side thereof:

• an objective optical system having a positive refracting power;
• an image-inverting optical system for erecting an intermediate image formed by said objective optical system;
• and
• an ocular optical system having a positive refracting power;
• wherein said objective optical system includes, in order from an object side thereof:
• a negative first unit;
• a positive second unit;
• and
• a positive third unit;
• wherein at least the first unit and the second unit are movable units moving when zooming is performed, and the third unit is formed from a prism including an image-inverting function, said prism including at least one reflecting surface having a rotationally asymmetric surface configuration, and said prism including at least one transmitting surface or reflecting surface that has a negative power, said third unit having a principal point positioned on a pupil side of a plane where the intermediate image is formed, and
• wherein a composite focal length of said movable units satisfies the following condition:
• 0.3<fmove/fW<0.9 (15)
• where fmove is the composite focal length of said movable units at a wide-angle end, and fW is a focal length of said objective optical system at the wide-angle end.

A finder optical system comprising, in order from an object side thereof:

• an objective optical system having a positive refracting power;
• an image-inverting optical system for erecting an intermediate image formed by said objective optical system;
• and
• an ocular optical system having a positive refracting power;
• wherein said objective optical system includes:
• an optical system having at least two movable units moving when zooming is performed, said optical system having a positive composite power;
• and
• a prism placed on a pupil side of said optical system, said prism including an image-inverting function, and said prism including at least one reflecting surface having a rotationally asymmetric surface configuration;
• wherein at least either one of a first transmitting surface and first reflecting surface of said prism has a negative power, and a second transmitting surface of said prism has a positive power, and
• wherein said finder optical system satisfies the following condition:
• 1.0<d/(fW·tan θw·Z)<2.5 (1)
• where d is a distance from an entrance surface of said objective optical system to a first reflecting surface of said image-inverting optical system at the wide-angle end;
• fW is a focal length of said objective optical system at a wide-angle end;
• θw is a maximum field angle of said objective optical system at the wide-angle end;
• and Z is a zoom ratio.

A finder optical system comprising, in order from an object side thereof:

• an objective optical system having a positive refracting power;
• an image-inverting optical system for erecting an intermediate image formed by said objective optical system;
• and
• an ocular optical system having a positive refracting power;
• wherein said objective optical system has:
• at least two movable units moving when zooming is performed;
• and
• a prism placed on an object side of the intermediate image formed by said objective optical system, said prism having three reflecting surfaces, wherein at least one of said reflecting surfaces has a rotationally asymmetric surface configuration, and
• wherein said finder optical system satisfies the following condition:
• 1.0<d/(fW·tan θw·Z)<2.5 (1)
• where d is a distance from an entrance surface of said objective optical system to a first reflecting surface of said image-inverting optical system at a wide-angle end;
• fW is a focal length of said objective optical system at a wide-angle end;
• θw is a maximum field angle of said objective optical system at the wide-angle end;
• and Z is a zoom ratio.

A finder optical system comprising, in order from an object side thereof:

• an objective optical system having a positive refracting power;
• an image-inverting optical system for erecting an intermediate image formed by said objective optical system;
• and
• an ocular optical system having a positive refracting power;
• wherein said objective optical system includes, in order from an object side thereof:
• a negative first unit;
• a positive second unit;
• and
• a negative third unit;
• wherein at least the first unit and the second unit are movable units moving when zooming is performed, and the third unit is formed from a prism including an image-inverting function, said prism including at least one reflecting surface having a rotationally asymmetric surface configuration, and
• wherein said finder optical system satisfies the following condition:
• 1.0<d/(fW·tan θw·Z)<2.5 (1)
• where d is a distance from an entrance Surface of said objective optical system to a first reflecting surface of said image-inverting optical system at a wide-angle end;
• fW is a focal length of said objective optical system at a wide-angle end;
• θw is a maximum field angle of said objective optical system at the wide-angle end;
• and Z is a zoom ratio.

A finder optical system comprising, in order from an object side thereof:

• an objective optical system having a positive refracting power;
• an image-inverting optical system for erecting an intermediate image formed by said objective optical system;
• and
• an ocular optical system having a positive refracting power;
• wherein said objective optical system includes, in order from an object side thereof:
• a negative first unit;
• a positive second unit;
• and
• a positive third unit;
• wherein at least the first unit and the second unit are movable units moving when zooming is performed, and the third unit is formed from a prism including an image-inverting function, said prism including at least one reflecting surface having a rotationally asymmetric surface configuration, and said prism including at least one transmitting surface or reflecting surface that has a negative power, said third unit having a principal point positioned on a pupil side of a plane where the intermediate image is formed, and
• wherein said finder optical system satisfies the following condition:
• 1.0<d/(fW·tan θw·Z)<2.5 (1)
• where d is a distance from an entrance Surface of said objective optical system to a first reflecting surface of said image-inverting optical system at a wide-angle end;
• fW is a focal length of said objective optical system at a wide-angle end;
• θw is a maximum field angle of said objective optical system at the wide-angle end;
• and Z is a zoom ratio.

A finder optical system comprising, in order from an object side thereof;

• an objective optical system having a positive refracting power;
• an image-inverting optical system for erecting an intermediate image formed by said objective optical system;
• and
• an ocular optical system having a positive refracting power,
• wherein said objective optical system has:
• at least two movable units moving when zooming is performed;
• and
• a prism placed on an object side of the intermediate image formed by said objective optical system, said prism including at least one reflecting surface having a rotationally asymmetric surface configuration;
• said image-inverting optical system including a Porro prism;
• said finder optical system satisfying the following conditions:
• 1.0<d/(fW·tan θw·Z)<2.5 (3)
• 0.5<dp/(fW·tan θw)<1.1 (4)
• where d is a distance from an entrance surface of said objective optical system to a first reflecting surface of said image-inverting optical system at the wide-angle end;
• fW is a focal length of said objective optical system at a wide-angle end;
• θw is a maximum field angle of said objective optical system at the wide-angle end;
• Z is a zoom ratio;
• and dp is a distance from an entrance surface of said image-inverting optical system placed on the object side of said intermediate image to said first reflecting surface.

A finder optical system comprising, in order from an object side thereof:

• an objective optical system having a positive refracting power;
• an image-inverting optical system for erecting an intermediate image formed by said objective optical system;
• and
• an ocular optical system having a positive refracting power;
• wherein said objective optical system has:
• at least two movable units moving when zooming is performed;
• and
• a prism placed on an object side of the intermediate image formed by said objective optical system, said prism having two reflecting surfaces, wherein at least one of said reflecting surfaces has a rotationally asymmetric surface configuration, and said prism constituting a part of said objective optical system and a part of said image-inverting optical system;
• said finder optical system satisfying the following condition:
• 0.5<dp/(fW·tan θW)<1.1 (9)
• where fW is a focal length of said objective optical system at a wide-angle end;
• θW is a maximum field angle of said objective optical system at the wide-angle end;
• and dp is a distance from an entrance surface of said prism placed on the object side of the intermediate image to a first reflecting surface thereof.

A finder optical system comprising, in order from an object side thereof:

• an objective optical system having a positive refracting power;
• an image-inverting optical system for erecting an intermediate image formed by said objective optical system;
• and
• an ocular optical system having a positive refracting power,
• wherein said objective optical system has:
• at least two movable units moving when zooming is performed;
• and
• a prism placed on an object side of the intermediate image formed by said objective optical system, said prism including two reflecting surfaces, both of said reflecting surfaces being independent of other transmitting and reflecting surfaces, at least one of said reflecting surfaces having a rotationally asymmetric surface configuration, said prism having an optical path in which an axial principal ray or a projective axial principal ray defined by projecting the axial principal ray onto a plane containing a part of the axial principal ray bends in a same direction with respect to a travel direction of light rays at said two reflecting surfaces, and said prism constituting a part of said objective optical system and a part of said image-inverting optical system;
• said finder optical system satisfying the following condition:
• 0.5<dp/(fW·tan θW)<1.1 (21)
• where dp is a distance from an entrance surface of said prism placed on the object side of the intermediate image to a first reflecting surface thereof;
• fW is a focal length of said objective optical system at a wide-angle end;
• θW is a maximum field angle of said objective optical system at the wide-angle end.