Observation device and image pickup apparatus including the same
An observation device according to the present invention includes an image display element displaying an image, and a finder optical system used for observing the image displayed on an image display surface of the image display element. The finder optical system includes a positive first lens, a negative second lens, and a biconvex positive third lens arranged in this order from the image display surface side to the observation side. A focal length of the second lens, a focal length of the finder optical system, a curvature radius of a lens surface of the second lens on the image display surface side, a curvature radius of a lens surface of the second lens on the observation side, a diagonal length of the image display surface, and a curvature radius of a lens surface of the third lens on the image display surface side are appropriately set.
1. An observation device, comprising:
an image display element that displays an image; and
a finder optical system that is used for observing the image displayed on an image display surface of the image display element, wherein
the finder optical system includes a first lens with a positive refractive power, a second lens with a negative refractive power, and a third lens with a positive refractive power arranged in this order from an image display surface side to an observation side, the third lens being biconvex, wherein
the following conditional expressions are satisfied:
−0.70< f 2/ f<− 0.20;
0.7<( R 22+ R 21)/( R 22− R 21)<1.4;
0.31< H/f< 0.50; and
0.000( R 31− R 22)/( R 31+ R 22)<10.0,
where f2 is a focal length of the second lens, f is a focal length of the finder optical system, R21 is a curvature radius of a lens surface of the second lens on the image display surface side, R22 is a curvature radius of a lens surface of the second lens on the observation side, H is a half of a diagonal length of the image display surface, and R31 is a curvature radius of a lens surface of the third lens on the image display surface side.
2. The observation device according to claim 1 , wherein the following conditional expression is satisfied:
−8.5<( R 21+ R 12)/( R 21− R 12)<−2.0,
where R12 is a curvature radius of a lens surface of the first lens on the observation side.
3. The observation device according to claim 1 , wherein the following conditional expression is satisfied:
0.30< f 1/ f< 1.00,
where f1 is a focal length of the first lens.
4. The observation device according to claim 1 , wherein the following conditional expression is satisfied:
0.50< f 3/ f 1<3.10,
where f1 is a focal length of the first lens, and f3 is a focal length of the third lens.
5. The observation device according to claim 1 , wherein
the second lens includes at least one aspherical surface, and
the following conditional expressions are satisfied:
1.58< nd< 1.95; and
15< vd< 32,
where nd is a refractive index on a d-line of a material forming the second lens, and vd is an Abbe number based on the d-line of the material forming the second lens.
6. The observation device according to claim 1 , wherein
the finder optical system enables diopter adjustment, and
a lens closest to the observation side in the finder optical system does not move for the diopter adjustment.
7. The observation device according to claim 1 , wherein
the finder optical system consists of the first lens, the second lens, the third lens, and a fourth lens with a positive refractive power arranged in this order from the image display surface side to the observation side.
8. The observation device according to claim 1 , wherein the following conditional expression is satisfied:
0.90< dL/f< 1.65,
where dL is a length on an optical axis with a diopter of −1 from a lens surface closest to the image display surface in the finder optical system to a lens surface closest to the observation side in the finder optical system.
9. An image pickup apparatus, comprising:
an image pickup element;
an image display element that displays an image obtained by the image pickup element; and
a finder optical system that is used for observing the image displayed on the image display element, wherein
the finder optical system includes a first lens with a positive refractive power, a second lens with a negative refractive power, and a third lens with a positive refractive power arranged in this order from an image display surface side to an observation side, the third lens being biconvex, wherein
the following conditional expressions are satisfied:
−0.70< f 2/ f<− 0.20;
0.7<( R 22+ R 21)/( R 22− R 21)<1.4;
0.31< H/f< 0.50; and
0.000≤( R 31− R 22)/( R 31+ R 22)<10.0,
where f2 is a focal length of the second lens, f is a focal length of the finder optical system, R21 is a curvature radius of a lens surface of the second lens on the image display surface side, R22 is a curvature radius of a lens surface of the second lens on the observation side, H is a half of a diagonal length of the image display surface, and R31 is a curvature radius of a lens surface of the third lens on the image display surface side.