JP2000347101A5 - - Google Patents

Claims (7)

An objective optical system having a positive refractive power, an image reversal optical system that inverts the upper and lower sides and the right and left of the intermediate image formed by the objective optical system, and a positive refractive power disposed in the vicinity of the imaging position of the intermediate image. In a real image finder having a field lens group having an eyepiece optical system having a positive refractive power,
The objective optical system includes a first lens group having a negative refractive power, a second lens group having a positive refractive power, and a third lens group having a positive refractive power, which are arranged in order from the object side. A fourth lens group having negative refractive power;
Each of the first lens group, the second lens group, and the third lens group is composed of one single lens,
The zooming from the wide-angle end to the telephoto end is performed by fixing the fourth lens group and moving the second lens group and the third lens group on the optical axis, and
A real image type zoom finder characterized by satisfying the following conditional expressions (1), (2) and (3).
3.5 <ft / fw <6.0 (1)
1.1 <f3 / fw <2.1 (2)
0.5 <ft / fr <1.5 (3)
Where fw is the focal length at the wide-angle end of the objective optical system, ft is the focal length at the telephoto end of the objective optical system, f3 is the focal length of the third lens group of the objective optical system, and fr is the fourth focal length of the objective optical system. The combined focal length from the lens group to the field lens group is shown. In a real image finder having an objective optical system having a positive refractive power, an image reversing optical system for inverting the upper and lower sides and the right and left of an intermediate image formed by the objective optical system, and an eyepiece optical system having a positive refractive power,
The objective optical system includes a first lens group having a negative refractive power, a second lens group having a positive refractive power, and a third lens group having a negative refractive power, which are arranged in order from the object side. A fourth lens group having positive refractive power,
Each of the first lens group, the second lens group, and the third lens group is composed of one single lens,
The zooming from the wide-angle end to the telephoto end is performed by fixing the first lens group and the fourth lens group and moving the second lens group and the third lens group on the optical axis, and
A real-image magnification finder that satisfies the following conditional expressions (1) and (4).
3.5 <ft / fw <6.0 (1)
0.5 <f2 / fw <1.5 (4)
Where fw is the focal length at the wide-angle end of the objective optical system, ft is the focal length at the telephoto end of the objective optical system, and f2 is the focal length of the second lens group of the objective optical system. The following conditional expression (Five) The real image type variable magnification finder according to claim 1, wherein:
2.6 <d12w / d23w (Five)
Here, d12w represents the distance between the first lens group and the second lens group at the wide angle end of the objective optical system, and d23w represents the distance between the second lens group and the third lens group at the wide angle end of the objective optical system. 4. The real image type variable magnification finder according to claim 1, wherein the first lens group is fixed during zooming. 5. The real image type zoom finder according to claim 1, wherein each of the first to fourth lens groups has at least one aspheric surface. 6. The real image variable magnification finder according to claim 1, wherein the field lens group is located closer to the eyepiece optical system than the intermediate image plane. 3. The real image variable magnification finder according to claim 2, wherein each of the first to fourth lens groups has at least one aspheric surface.