JP7775005B2 - Observation optical system and observation device having the same - Google Patents

Description

The present invention relates to an observation optical system, and in particular to an observation optical system, such as a telescope or binoculars, in which an image formed by an objective optical system is observed through an eyepiece optical system.

Observation optical systems such as those described above are desired to be compact while having a large aperture and high magnification.

The specifications of binoculars that use observation optical systems are determined by the aperture and magnification of the lens closest to the object in the binoculars' objective optical system; the larger the aperture, the heavier the binoculars. Magnification is also determined by the ratio of the focal length of the objective optical system to the focal length of the eyepiece optical system; to increase magnification, the focal length of the objective optical system must be lengthened or the focal length of the eyepiece optical system must be shortened, both of which result in larger and heavier binoculars. In other words, when attempting to achieve a large aperture and high magnification in binoculars, the bundle of rays passing through the objective optical system becomes larger, so the number of lenses required to correct aberrations such as spherical aberration and field curvature must be increased, the overall length of the objective optical system becomes longer, and the binoculars become larger.

In addition, the higher the magnification, the larger the image being observed, making hand shake more noticeable. To address this, adding an anti-vibration function makes the binoculars heavier.

Therefore, if you add vibration-reduction features to binoculars with large apertures and high magnification, they will tend to become larger and heavier.

In addition, a prism vibration isolation mechanism that uses an image-inverting optical system (image-inverting prism) to isolate images is known as a mechanism that can handle significant camera shake isolation in large-diameter, high-magnification binoculars. In this prism vibration isolation mechanism, the image-inverting prisms (roof prism, auxiliary prism) move together on the left and right. In a prism vibration isolation mechanism, an interpupillary distance adjustment prism is located on the observation side of the image-inverting prism to adjust the interpupillary distance between the left and right eyes. As a result, a longer optical path length is required for the three prisms: the roof prism, auxiliary prism, and interpupillary distance adjustment prism.

Therefore, in order to miniaturize an observation optical system equipped with this prism vibration isolation mechanism, it is necessary to miniaturize the objective optical system, which is located between the object-side surface of the objective optical system and the object-side surface of the image-inverting optical system.

Patent Document 1 discloses an observation optical system in which a lens with strong negative refractive power is placed immediately before the object side of an image-inverting optical system (image-inverting prism), and a lens with positive refractive power is placed on the object side of that. In Patent Document 1, the distance from the lens surface of the objective optical system closest to the object to the object-side surface of the image-inverting optical system is set shorter than the distance from the lens surface of the objective optical system closest to the object to the lens surface of the eyepiece optical system on the observation side. The objective optical system in Patent Document 1 is composed of one positive lens and one negative lens, and the focal length of the objective optical system is set to 80 mm. This enables the objective optical system to be made compact.

Patent Document 2 discloses an observation optical system in which a lens with strong negative refractive power is placed immediately before the object side of an image-inverting optical system, and a lens group whose combined focal length is a positive focal length is placed on the object side of that lens group. In Patent Document 2, the distance from the lens surface of the objective optical system closest to the object side to the object-side surface of the image-inverting optical system is set shorter than the distance from the lens surface of the objective optical system closest to the object side to the lens surface of the eyepiece optical system on the observation side. The objective optical system in Patent Document 2 is composed of a positive-negative cemented lens, a positive lens, a positive lens, and a negative lens, and the focal length of the objective optical system is set to approximately 160 mm to 180 mm. This enables the objective optical system to be made compact.

Japanese Patent Application Publication No. 8-220423 JP 2016-166907 A

However, in the observation optical system of Patent Document 1, the focal length of the objective optical system is short, and in order to achieve a high magnification of over 20x and a large aperture, the system requires only two lenses, which is advantageous in terms of size, but it does not provide sufficient correction for spherical aberration and field curvature, and good optical performance cannot be achieved.

Furthermore, in the observation optical system of Patent Document 2, the focal length of the objective optical system is short, and increasing the magnification to over 20x and increasing the aperture would result in an increase in size. Furthermore, the distance from the object side of the image-inverting optical system to the image side of the eyepiece optical system is short, and there is no space to place the image-inverting optical system and the interpupillary distance adjustment prism, making it difficult to place a prism vibration isolation mechanism to move the image-inverting optical system.

The objective of the present invention is to provide an observation optical system that has a large aperture and high magnification, yet is compact even when equipped with an anti-vibration mechanism that moves the image-inverting optical system.

An observation optical system according to one aspect of the present invention comprises an objective optical system, an image-inverting optical system, and an eyepiece optical system, arranged in this order from the object side to the observation side, and wherein an image formed by the objective optical system is magnified and observed by the eyepiece optical system, the objective optical system comprising, arranged in this order from the object side to the observation side, a first lens group having positive refractive power and a first lens element having the strongest negative refractive power within the objective optical system, wherein the focal length of the objective optical system is fo, the focal length of the first lens element is fn, the optical path length along the optical axis from the lens surface of the objective optical system closest to the object side to the lens surface of the eyepiece optical system closest to the observation side is L, the optical path length along the optical axis from the surface of the image-inverting optical system closest to the object side to the lens surface of the eyepiece optical system closest to the observation side is l , and the focal length of the eyepiece optical system is fe ,
-15.00<fо/fn<-3.00
0.70<l/L<0.90
15.0<fо/fe<40.0
The present invention is characterized in that the following conditional expression is satisfied:

Other objects and features of the present invention are described in the following embodiments.

The present invention makes it possible to provide an observation optical system that has a large aperture and high magnification, yet is compact even when equipped with an anti-vibration mechanism that moves the image-inverting optical system.

FIG. 2 is a cross-sectional view of a lens of the observation optical system of Example 1. 3A to 3C are aberration diagrams of the observation optical system of Example 1. FIG. 10 is a cross-sectional view of a lens of an observation optical system according to a second embodiment. 10A to 10C are aberration diagrams of the observation optical system of Example 2. FIG. 10 is a cross-sectional view of a lens of an observation optical system according to a third embodiment. 10A to 10C are aberration diagrams of the observation optical system of Example 3. FIG. 10 is a cross-sectional view of a lens of an observation optical system according to a fourth embodiment. 10A to 10C are aberration diagrams of the observation optical system of Example 4. FIG. 10 is a cross-sectional view of a lens of an observation optical system according to a fifth embodiment. 10A to 10C are aberration diagrams of the observation optical system of Example 5. FIG. 10 is a cross-sectional view of a lens of an observation optical system according to a sixth embodiment. 13A to 13C are aberration diagrams of the observation optical system of Example 6. FIG. 13 is a cross-sectional view of a lens of an observation optical system according to a seventh embodiment. 13A to 13C are aberration diagrams of the observation optical system of Example 7. FIG. 13 is a cross-sectional view of a lens of an observation optical system according to an eighth embodiment. 13A to 13C are aberration diagrams of the observation optical system of Example 8. FIG. 1 is an explanatory diagram showing a binocular configuration. FIG. 2 is an explanatory diagram of an image-inverting optical system and a prism for adjusting an eye distance.

The following describes the observation optical systems and observation devices incorporating the optical systems according to each embodiment, with reference to the accompanying drawings.

Figures 1, 3, 5, 7, 9, 11, 13, and 15 are cross-sectional views of the lenses of the observation optical systems of Examples 1, 2, 3, 4, 5, 6, 7, and 8, respectively.

Figures 2, 4, 6, 8, 10, 12, 14, and 16 are afocal aberration diagrams of the observation optical systems of Examples 1, 2, 3, 4, 5, 6, 7, and 8, respectively.

The observation optical system in Example 1 has an aperture of φ50.8 mm and a magnification of 25.0x.

The observation optical system in Example 2 has an aperture of φ50.1 mm and a magnification of 25.0x.

The observation optical system in Example 3 has an aperture of φ51.1 mm and a magnification of 30.0x.

The observation optical system in Example 4 has an aperture of φ52.5 mm and a magnification of 30.0x.

The observation optical system in Example 5 has an aperture of φ51.1 mm and a magnification of 30.0x.

The observation optical system in Example 6 has an aperture of φ51.5 mm and a magnification of 30.0x.

The observation optical system in Example 7 has an aperture of φ51.1 mm and a magnification of 30.0x.

The observation optical system in Example 8 has an aperture of φ51.8 mm and a magnification of 31.0x.

The observation optical systems of each embodiment are used as observation optical systems for telescopes, binoculars, finder systems, etc. In the case of binoculars, a pair of observation optical systems, one on each side, constitutes the binocular optical system.

The observation optical system in each embodiment has a prism vibration reduction function that reduces camera shake by moving the image inversion optical system (prism).

In each lens cross-sectional view, the left is the object side (front) and the right is the observation side (rear). The observation optical system in each embodiment is composed of an objective optical system o, an image-inverting optical system z, an eye-distance adjusting prism m, and an eyepiece optical system e, arranged in that order from the object side to the observation side.

In each embodiment, L1 is the first lens group (or first group) with positive refractive power (optical power = the reciprocal of the focal length), and lens element N (first lens element) is a lens element with negative refractive power. Lens element f (second lens element) is a lens element with positive refractive power. Here, the lens group may be composed of one lens or multiple lenses. The lens element refers to a single lens or a cemented lens composed of multiple lenses, and does not include a lens group composed of multiple lenses with an air gap between them. Furthermore, an intermediate image is formed within the eyepiece optical system e. EP is the pupil position.

The spherical aberration diagram shows the amount of spherical aberration for the d-line (wavelength 587.6 nm), g-line (wavelength 435.8 nm), F-line (486.1 nm), and C-line (656.3 nm). In the astigmatism diagram, S shows the amount of astigmatism on the sagittal image plane, and M shows the amount of astigmatism on the meridional image plane. The distortion diagram shows the amount of distortion for the d-line. The chromatic aberration diagram shows the amounts of chromatic aberration for the g-line, F-line, and C-line. ω is the half angle of view (°).

Using Figure 17, we will explain binoculars as an observation device 100 with prism vibration isolation. Figure 17 shows an observation device 100 equipped with a pair of observation optical systems, one on the left and one on the right.

In Figure 17, the upper side is the object side and the lower side is the observation side. The observation optical system (first observation optical system) 100A on the left side is composed of, arranged in order from the object side to the observation side, an objective optical system o1, an image-inverting optical system z1 (auxiliary prism h1, roof prism dp1), an interpupillary distance adjusting prism m1, and an eyepiece optical system e1. The observation optical system 100B on the right side is composed of, arranged in order from the object side to the observation side, an objective optical system o2, an image-inverting optical system z2 (auxiliary prism h2, roof prism dp2), an interpupillary distance adjusting prism m2, and an eyepiece optical system e2. The observation optical system 100A on the left side is for the left eye, and the observation optical system 100B on the right side is for the right eye. The observation optical systems 100A and 100B are arranged in parallel. The objective optical systems o1 and o2, the image-inverting optical systems z1 and z2, the interpupillary distance adjusting prisms m1 and m2, and the eyepiece optical systems e1 and e2 are all identical. The observation optical systems 100A and 100B are configured to be the same for both the left and right eyes. k1 and k2 indicate the optical paths of light rays passing through the left and right eyes, respectively. Light rays k1 and k2 travel from the object side above to the observation side below, and enter the left and right eyes after passing through the eyepiece optical systems e1 and e2. This allows observation to be performed.

Light rays k1 and k2 are reflected within the image-inverting optical systems z1 and z2. As a result, light rays k1 and k2 are inverted 180 degrees, and when the subject image is observed through the eyepiece optical systems e1 and e2, the subject image is observed as an erect image. Furthermore, because light rays k1 and k2 are reflected within the interpupillary distance adjusting prisms m1 and m2, the ray spacing B between the eyepiece optical systems e1 and e2 becomes wider than the ray spacing A between the objective optical systems o1 and o2.

Figure 18 shows the details of the optical path of ray k from the image-inverting optical system z to the interpupillary distance adjustment prism m. The left side is the object side. Ray k passes through the image-inverting optical system z (auxiliary prism h, roof prism dp) and the interpupillary distance adjustment prism m, and proceeds to the observation side. The interpupillary distance can be adjusted by rotating the interpupillary distance adjustment prism m in a direction perpendicular to the axis of ray k, as indicated by arrow y in the figure, relative to the axis of the light entering the interpupillary distance adjustment prism m.

Returning to Figure 17, we will explain the prism vibration-proof structure.

Image-inverting prism unit b (anti-vibration unit b), which is composed of a pair of left and right image-inverting optical systems z1 and z2, is moved parallel and/or tilted to compensate for camera shake. The parallel and/or tilted decentering movement of anti-vibration unit b is performed using an actuator or similar. The lighter the anti-vibration unit b, the smaller the actuator can be, allowing for a lighter anti-vibration unit b. Furthermore, to reduce the weight of the mechanical components that hold the image-inverting optical systems z1 and z2, the image-inverting optical systems z1 and z2 are positioned closely together. Positioning the image-inverting optical systems z1 and z2 closely together results in the distance A between the objective optical systems o1 and o2 being smaller than the interpupillary distance. This makes binocular observation difficult. Therefore, interpupillary distance-adjusting prisms m1 and m2 are used to make the distance B between the eyepiece optical systems e1 and e2 wider than the distance A between the objective optical systems o1 and o2. Interpupillary distance adjustment can be achieved by rotating the interpupillary distance adjusting prism m in a direction perpendicular to the light ray k, as shown by arrow y in Figure 18. The objective optical systems o1, o2 and image-inverting optical systems z1, z2 can be integrated into an integrated structure C, the interpupillary distance adjusting prism m1 and eyepiece optical system e1 can be integrated into an eyepiece unit D1, and the interpupillary distance adjusting prism m2 and eyepiece optical system e2 can be integrated into an eyepiece lens unit D2, thereby making it possible to reduce the size of the observation device 100. Therefore, when using an anti-vibration mechanism that moves the left and right image-inverting optical systems z1, z2 as a single unit, a prism anti-vibration structure is required from the image-inverting optical systems z1, z2 to the interpupillary distance adjusting prisms m1, m2.

Figures 1 (Example 1), 3 (Example 2), 5 (Example 3), 7 (Example 4), 9 (Example 5), 11 (Example 6), 13 (Example 7), and 15 (Example 8) are cross-sectional views of the lenses of the observation optical system when the optical path length of the eye-distance adjusting prism m is converted into a straight line. Here, the optical path length refers to the length of the optical path traveled by a light ray within the image-inverting optical system z (prism, etc.).

As mentioned above, in Figures 1, 3, 5, 7, 9, 11, 13, and 15, if the distance L from the object side of the objective optical system o to the image side of the eyepiece optical system e can be shortened within the structural constraints of the vibration isolation structure from the image-inverting optical system z to the eye-distance adjustment prism m, the observation device 100 can be made smaller.

If the image-inverting optical systems z1 and z2 are used as vibration-proof mechanisms, the optical path length required from the image-inverting optical systems z1 and z2 to the interpupillary distance adjustment prisms m1 and m2 is significant. Therefore, miniaturizing the objective optical systems o1 and o2 or the eyepiece optical systems e1 and e2 allows for the miniaturization of the observation device 100. Here, increasing the aperture increases the lens diameter of the objective optical systems o1 and o2 closest to the object. Furthermore, increasing the magnification increases the focal length of the objective optical systems o1 and o2, increasing the overall size of the objective optical systems o1 and o2. In Figure 17, the objective optical systems o1 and o2 to the image-inverting optical systems z1 and z2 form an integrated structure C. Therefore, if the objective optical systems o1 and o2 become larger due to a larger aperture and higher magnification, the mechanical holding components become larger, and the integrated structure C also becomes larger. In other words, the observation device 100 becomes larger and heavier. Therefore, miniaturizing the objective optical systems o1 and o2 within the integrated structure C allows for the miniaturization of the observation device 100. In other words, in each lens cross-sectional view, if the ratio of distance l to distance L is increased, the distance from the object side surface of objective optical system o to the object side surface of image-inverting optical system z can be shortened. This makes it possible to reduce the size of the integrated structure C from objective optical systems o1 and o2 to image-inverting optical systems z1 and z2 serving as an anti-vibration mechanism. Here, distance L is the distance from the object side surface of objective optical system o to the image side surface of eyepiece optical system e. Furthermore, distance l is the distance from the object side surface of image-inverting optical system z to the image side surface of the eyepiece optical system.

In order to miniaturize the objective optical system о while achieving a large aperture and high magnification, the objective optical system о has, arranged in order from the object side to the observation side, a first lens unit L1 with positive refractive power and a lens element N with the strongest negative refractive power within the objective optical system о.

The objective optical system o of Examples 1, 2, 3, 4, and 5 is composed of, arranged in order from the object side to the observation side, a first lens unit L1 with positive refractive power and a lens element N with the strongest negative refractive power in the objective optical system. The first lens unit L1 is composed of, in order from the object side, a first lens 11 with positive refractive power, a cemented lens of a second lens 12 with positive refractive power and a third lens 13 with negative refractive power, and a fourth lens 14 with positive refractive power. The lens element N with negative refractive power is composed of a cemented lens of a lens with positive refractive power and a lens with negative refractive power.

The objective optical system o of Example 6 is composed of, arranged in order from the object side to the observation side, a first lens unit L1, a lens element N, and a lens with positive refractive power. The first lens unit L1 is composed of, from the object side, a first lens 11 with positive refractive power, a cemented lens of a second lens 12 with positive refractive power and a third lens 13 with negative refractive power, and a fourth lens 14 with positive refractive power. The lens element N with negative refractive power is composed of a cemented lens of a lens with positive refractive power and a lens with negative refractive power.

The objective optical system o of Examples 7 and 8 is composed of, arranged in order from the object side to the observation side, a first lens unit L1, a lens element N, and a lens with negative refractive power. The first lens unit L1 is composed of, from the object side, a first lens 11 with positive refractive power, a cemented lens of a second lens 12 with positive refractive power and a third lens 13 with negative refractive power, and a fourth lens 14 with positive refractive power. The lens element N with negative refractive power is composed of a cemented lens of a lens with positive refractive power and a lens with negative refractive power.

In order to guide the large bundle of rays from the objective optical system о to the small aperture of the image-inverting optical system z, the bundle of rays is converged by the first lens unit L1, which has a strong positive refractive power. Then, in order to pass the converged bundle of rays from the image-inverting optical system z to the eye-distance adjusting prism m, a lens element N, which has a strong negative refractive power, is positioned on the observation side of the objective optical system о. Since the focal length of the objective optical system о increases to achieve higher magnification, the objective optical system о is designed to have a long focal length relative to its overall length, resulting in a large telephoto ratio.

In each embodiment, the first lens 11 and second lens 12 of the objective optical system are made of glass material with anomalous dispersion to correct the secondary spectrum of axial chromatic aberration corresponding to the high magnification specifications.

To accommodate high magnification specifications, the focal length of the objective optical system о can be increased, but the longer the focal length of the objective optical system о, the worse the axial chromatic aberration becomes. Therefore, by using glass materials with high anomalous dispersion for the first lens 11, which is closest to the object and bends the large light beam entering the objective optical system о, and the second lens 12, which is located next to it, it is possible to correct the secondary spectrum of axial chromatic aberration.

In each embodiment, focusing from infinity to close range is performed by moving the lens element f toward the object, as shown by the arrow in the figure. In the case of a large-diameter, high-magnification objective optical system о, the outer diameter is increased accordingly. Therefore, if focusing is performed by moving some of the lenses within the objective optical system о, the mechanical mechanism can be made more compact. Furthermore, a structure in which the front lens remains stationary during focusing is convenient when incorporating a waterproof mechanism. If focusing is performed by moving a lens on the object side of the objective optical system о or by moving the entire objective optical system о, a flat plate must be placed on the object side of the objective optical system о, resulting in increased size. The method of focusing by partially moving a lens on the observation side of the front lens in the objective optical system о is known as inner focusing. In this way, using an inner focusing type allows for the mechanical mechanism to be made more compact, or for the waterproof mechanism to be made smaller, thereby reducing the overall size of the observation device 100.

In each embodiment, diopter adjustment can be achieved by moving the lens element f or by moving the entire eyepiece optical system e.

Next, we will describe the characteristic configuration of the observation optical system in each embodiment.

The observation optical system in each embodiment has a large aperture and high magnification, but also has a prism vibration isolation mechanism that moves the image-inverting optical system z to provide vibration isolation, allowing for compact size.

The observation optical system in each embodiment has, arranged in order from the object side to the observation side, an objective optical system o, an image-inverting optical system z, and an eyepiece optical system e, and is an observation optical system for magnifying and observing an image formed by the objective optical system o using the eyepiece optical system e. The objective optical system o has, arranged in order from the object side to the observation side, a first lens unit L1 with positive refractive power and a lens element N with the strongest negative refractive power within the objective optical system o.

The observation optical system of each embodiment satisfies the following conditional expressions (1) and (2).

-15.00 < fо/fn < -3.00 ... (1)
0.70 < l/L < 0.90...(2)
Here, f0 is the focal length of the objective optical system o, and fn is the focal length of the lens element N. L is the optical path length along the optical axis from the lens surface of the objective optical system o closest to the object to the lens surface of the eyepiece optical system e closest to the observation side. l is the optical path length along the optical axis from the lens surface of the image-inverting optical system z closest to the object to the lens surface of the eyepiece optical system e closest to the observation side.

Conditional expression (1) defines the ratio between the focal length f o of objective optical system o and the focal length f n of lens element N, which has the strongest negative refractive power within objective optical system o. If the upper limit of conditional expression (1) is exceeded, the focal length of lens element N becomes too long, making it difficult to reduce the beam of light incident on image-inverting optical system z. This results in a larger image-inverting optical system z. If the aperture diameter of the entrance surface of image-inverting optical system z becomes larger, an optical path length proportional to the aperture size of image-inverting optical system z is required, resulting in a larger image-inverting optical system z and, consequently, an actuator for the vibration isolation mechanism. If the lower limit of conditional expression (1) is exceeded, the focal length of lens element N becomes too short, reducing the beam of light incident on image-inverting optical system z. This is advantageous for miniaturizing image-inverting optical system z, but a shorter negative focal length results in a larger field curvature in the observation optical system on the overside, making correction difficult.

Conditional expression (2) defines the ratio of the optical path length from the lens surface of the objective optical system о closest to the object to the lens surface of the eyepiece optical system e closest to the observation side to the optical path length from the lens surface of the image-inverting optical system z closest to the object to the lens surface of the eyepiece optical system e closest to the observation side. If the upper limit of conditional expression (2) is exceeded, and the distance from the lens surface of the image-inverting optical system z closest to the object side to the lens surface of the eyepiece optical system e closest to the observation side becomes large, the space available for arranging the objective optical system о becomes too small, making it difficult to arrange an objective optical system о with a large aperture and high magnification. Furthermore, in order to arrange the objective optical system о, the focal length of lens element N must be reduced, which increases the curvature of field to the over-field side and makes correction difficult. Furthermore, if the distance from the lens surface of the image-inverting optical system z closest to the object side to the lens surface of the eyepiece optical system e becomes small, and the lower limit of conditional expression (2) is not reached, the space available for the objective optical system о becomes too large, and the observation optical system becomes large.

Furthermore, it is preferable that the numerical ranges of conditional expressions (1) and (2) satisfy the ranges of the following conditional expressions (1a) and (2a).

-12.00 < fо/fn < -3.50 ... (1a)
0.71 < l/L < 0.85...(2a)
It is more preferable that the numerical ranges of the conditional expressions (1) and (2) satisfy the ranges of the following conditional expressions (1b) and (2b).

-9.00 < fо/fn < -3.70 ... (1b)
0.715 < l/L < 0.820...(2b)
As described above, according to each embodiment, it is possible to realize an observation optical system that has a large aperture and high magnification, yet is compact even when an anti-vibration mechanism that moves the image-inverting optical system z (prism) is installed.

Next, we will discuss the conditions that the observation optical system of each embodiment should preferably satisfy. The observation optical system of each embodiment should preferably satisfy one or more of the following conditional expressions.

-3.00 < f1/fn < -0.80 ... (3)
3.50 < fо/dо < 10.00...(4)
0.15 < f1/fо < 0.50 (5)
1.80 < φо/φp < 2.60 (6)
0.05 < np-nn < 0.50 (7)
1.00 < (nR1-nR2)/(nR1+nR2) < 5.00 (8)
0.05 < dn/dо < 0.50 (9)
-0.90 < (fR1-fR2)/(fR1+fR2) < -0.05...(10)
0.50 < fо/ff < 3.00 (11)
15.00 < fо/fe < 40.00...(12)
θgF-(-1.665×10 ^-7・νd ³ +5.213×10 ⁻⁵・νd ² −5.656×10 ⁻³・νd+0.737)> 0 ... (13)
60.0 < νd < 100.0 (14)
Here, f1 is the focal length of the first lens unit L1, which is arranged closer to the object than lens element N in the objective optical system o. dO is the distance on the optical axis from the lens surface closest to the object in the objective optical system o to the surface closest to the object in the image-inverting optical system z. φO is the outer diameter of the lens closest to the object in the objective optical system o. φp is the outer diameter of the lens closest to the object in the image-inverting optical system z. np is the refractive index of the lens with positive refractive power that constitutes lens element N. nn is the refractive index of the lens with negative refractive power that constitutes lens element N. Lens element N is composed of a cemented lens of a lens with positive refractive power and a lens with negative refractive power. nR1 is the radius of curvature of the lens surface closest to the object in lens element N. nR2 is the radius of curvature of the lens surface closest to the observation side in lens element N. dn is the distance on the optical axis from the lens surface closest to the observation side in lens element N to the surface closest to the object in the image-inverting optical system z. fR1 is the radius of curvature of the lens surface of lens element f closest to the object. fR2 is the radius of curvature of the lens surface of lens element f closest to the observation side. ff is the focal length of lens element f. fe is the focal length of eyepiece optical system e. θgF and νd are the partial dispersion ratio and Abbe number of the glass materials of first lens 11 and second lens 12, respectively.

Conditional expression (3) defines the ratio between the focal length f1 of the first lens unit L1, which is located closer to the object than lens element N, and the focal length fn of lens element N. Exceeding the upper limit of conditional expression (3) makes the focal length of lens element N too long, preventing light rays from passing through the image-inverting optical system z. To allow light rays to pass through, the image-inverting optical system z must be enlarged, which is undesirable as the observation optical system becomes larger. Exceeding the upper limit of conditional expression (3) also shortens the focal length of objective optical system о, undesirably increasing spherical aberration on the underside. Falling below the lower limit of conditional expression (3) makes the focal length of lens element N too short, which is advantageous for reducing the overall length of the observation optical system, but increases spherical aberration and field curvature on the overside. Furthermore, the shorter focal length of lens element N increases the lens curvature and weight, undesirably increasing the lens's mass.

Conditional expression (4) defines the ratio of the focal length fO of the objective optical system o to the distance dO from the lens surface of the objective optical system o closest to the object to the surface of the image-inverting optical system z closest to the object. If the upper limit of conditional expression (4) is exceeded, the distance from the lens surface of the objective optical system o closest to the object to the surface of the image-inverting optical system z closest to the object becomes too short. Therefore, in order to position the objective optical system o, it is necessary to shorten the focal lengths of the lens element N and the first lens unit L1 located on the object side, which undesirably increases the lens curvature and weight. If the lower limit of conditional expression (4) is exceeded, the distance from the lens surface of the objective optical system o closest to the object to the surface of the image-inverting optical system z closest to the object becomes too long, which undesirably increases the size of the objective optical system o.

Conditional expression (5) defines the ratio between the focal length f1 of the first lens unit L1, which is located closer to the object than the lens element N, and the focal length f0 of the objective optical system o. Exceeding the upper limit of conditional expression (5) is undesirable because the focal length of the first lens unit L1 becomes longer, making the objective optical system o larger, or the focal length of the objective optical system o becomes too short, making it difficult to meet the high magnification specification. Falling below the lower limit of conditional expression (5) is undesirable because the focal length of the objective optical system o becomes longer, which is advantageous for meeting the high magnification specification, but the focal length of the first lens unit L1 becomes too short, increasing spherical aberration and curvature of field on the underside.

Conditional formula (6) defines the ratio between the outer diameter φо of the lens closest to the object in the objective optical system о and the outer diameter φp of the image-inverting optical system closest to the object. In each embodiment, the outer diameter is 1 mm larger than the effective diameter. If the upper limit of conditional formula (6) is exceeded, the diameter of the light beam entering the objective optical system о increases, and the light beam must be reduced in size to enter the image-inverting optical system z. This requires increasing the focal length of the first lens unit L1, which is located closer to the object than lens element N, and shortening the focal length of lens element N. This increases the curvature of the objective optical system о, undesirably increasing the weight of the lens. If the lower limit of conditional formula (6) is exceeded, the size of the image-inverting optical system z increases, undesirably increasing the size of the vibration-proofing mechanism.

Conditional formula (7) defines the difference between the refractive index np of the lens with positive refractive power and the refractive index nn of the lens with negative refractive power in lens element N, and is intended to improve correction of spherical aberration and curvature of field. Exceeding the upper limit of conditional formula (7) is undesirable because the spherical aberration and curvature of field will be over-corrected to the excessive extent, making it impossible to achieve good optical performance. Conversely, falling below the lower limit of conditional formula (7) is undesirable because the spherical aberration and curvature of field will be under-corrected, making it impossible to achieve good optical performance.

Conditional expression (8) defines the shape factor of lens element N. Exceeding the upper limit of conditional expression (8) is undesirable because the focal length of the air lens between lens element N and the object-side lens becomes short, spherical aberration and field curvature become undercorrected, and good optical performance cannot be obtained. Failing to exceed the lower limit of conditional expression (8) is undesirable because the focal length of the air lens between lens element N and the object-side lens becomes long, spherical aberration and field curvature become overcorrected, and good optical performance cannot be obtained.

Conditional expression (9) defines the ratio of the distance dn from the lens surface of lens element N closest to the observation side to the surface of image-inverting optical system z closest to the object, to the distance dо from the lens surface of objective optical system о closest to the object to the surface of image-inverting optical system z closest to the object. Exceeding the upper limit of conditional expression (9) shortens the distance between the lenses in objective optical system о. Therefore, to achieve the specified magnification, the focal length of lens element N must be shortened. A shorter focal length of lens element N undesirably increases the lens curvature and weight, which is undesirable. Falling below the lower limit of conditional expression (9) allows for more leeway in lens arrangement within objective optical system о, making it easier to correct spherical aberration and field curvature, but it also undesirably causes interference between lens element N and image-inverting optical system z.

Conditional expression (10) defines the shape factor of lens element f. The observation optical systems of each embodiment are configured to perform inner focusing using lens element f, which has a meniscus shape convex toward the object side. Exceeding the upper limit of conditional expression (10) reduces the difference in curvature between the object-side and observation-side surfaces of lens element f, increasing the amount of movement of lens element f during focusing and undesirably increasing the size of the objective optical system o. Falling below the lower limit of conditional expression (10) undesirably increases the difference in curvature between the object-side and observation-side surfaces of lens element f, increasing spherical aberration and fluctuations in field curvature during focusing.

Conditional expression (11) defines the ratio between the focal length f o of the objective optical system o and the focal length ff of the lens element f. The observation optical systems in each embodiment are configured to perform inner focusing using the lens element f. Exceeding the upper limit of conditional expression (11) is undesirable because the focal length of lens element f becomes too short, resulting in large fluctuations in spherical aberration and field curvature due to focusing. Falling below the lower limit of conditional expression (11) is undesirable because the focal length of lens element f becomes too long, increasing the amount of movement of lens element f due to focusing and resulting in a large objective optical system o.

Conditional expression (12) defines the ratio between the focal length f o of the objective optical system o and the focal length fe of the eyepiece optical system e, and also defines the magnification of the observation optical system. Exceeding the upper limit of conditional expression (12) increases the focal length of the objective optical system o, which is advantageous for high-magnification specifications. However, when the focal length of the objective optical system o increases, it becomes necessary to shorten the focal length f1 of the first lens unit L1, which is located closer to the object than lens element N, and to shorten the focal length of lens element N in order to shorten the overall length of the objective optical system o. This requires a stronger lens curvature, which undesirably increases the weight of the objective optical system o. Falling below the lower limit of conditional expression (12) is undesirable because it becomes impossible to meet the specified high-magnification magnification.

Conditional expressions (13) and (14) define the partial dispersion ratio θgF and Abbe number νd of the first lens 11 and the second lens 12. Failing to satisfy conditional expression (13) is undesirable because it worsens the secondary spectrum of axial chromatic aberration. Satisfying conditional expression (13) while exceeding the upper limit of conditional expression (14) allows for good correction of the secondary spectrum of axial chromatic aberration, but no glass material is available. Satisfying conditional expression (13) while falling below the lower limit of conditional expression (14) allows for good correction of the secondary spectrum of axial chromatic aberration. However, this is undesirable because it reduces the difference in Abbe numbers between the second lens 12 and the third lens 13, making the radius of curvature of the cemented lens formed by the second lens 12 and the third lens 13 for chromatic aberration correction tighter and increasing the lens weight.

Furthermore, it is preferable that the numerical ranges of conditional expressions (3) to (14) be within the ranges of the following conditional expressions (3a) to (14a).

-2.50 < f1/fn < -0.85 ... (3a)
3.60 < fо/dо < 8.00...(4a)
0.17 < f1/fо < 0.40 ... (5a)
1.90 < φо/φp < 2.55 ... (6a)
0.08<np-nn<0.45...(7a)
1.10 < (nR1-nR2)/(nR1+nR2) < 3.00...(8a)
0.06 < dn/dо < 0.45...(9a)
-0.80 < (fR1-fR2)/(fR1+fR2) < -0.08...(10a)
0.60 < fо/ff < 2.50 (11a)
20.00 < fо/fe < 33.00...(12a)
θgF-(-1.665×10 ^-7・νd ³ +5.213×10 ⁻⁵・νd ² −5.656×10 ⁻³・νd+0.737)> 0 ... (13a)
70.0 < νd < 100.0 (14a)
It is more preferable that the numerical ranges of the conditional expressions (3) to (14) are within the ranges of the following conditional expressions (3b) to (14b).

-2.00 < f1/fn < -0.90 (3b)
3.70 < fо/dо < 6.00...(4b)
0.20 < f1/fо < 0.35...(5b)
1.95 < φо/φp < 2.50...(6b)
0.10<np-nn<0.40...(7b)
1.20 < (nR1-nR2)/(nR1+nR2) < 2.00...(8b)
0.07 <dn/dо<0.39...(9b)
-0.70 < (fR1-fR2)/(fR1+fR2) < -0.10...(10b)
0.70 < fо/ff < 1.75...(11b)
24.5 < fо/fe < 31.5...(12b)
θgF-(-1.665×10 ^-7・νd ³ +5.213×10 ⁻⁵・νd ² −5.656×10 ⁻³・νd+0.737)> 0 ... (13b)
80.0 < νd < 100.0 (14b)
In the observation optical system of each embodiment, by configuring each element as described above, it is possible to achieve a large aperture and high magnification, yet remain compact even when equipped with a prism-based vibration isolation mechanism, and to provide excellent correction for spherical aberration, field curvature, and axial chromatic aberration.

Next, we will explain the configurations that each component of the observation optical system in each embodiment should preferably satisfy.

In the objective optical system о, the first lens group L1 preferably comprises a total of four lenses, arranged in order from the object side: a first lens 11 with positive refractive power, a cemented lens consisting of a second lens 12 with positive refractive power and a third lens 13 with negative refractive power, and a fourth lens 14 with positive refractive power. The diameter of the lens closest to the object side of the objective optical system о is the largest, but by using a single lens as the cemented lens, weight can be reduced. Furthermore, by arranging a cemented lens consisting of a second lens 12 with positive refractive power and a third lens 13 with negative refractive power on the observation side, spherical aberration and axial chromatic aberration due to high magnification are effectively corrected. Furthermore, by arranging a fourth lens 14(f) with a meniscus shape facing the object side on the observation side and configuring it to move during focusing, fluctuations in spherical aberration and field curvature due to focusing are effectively corrected.

Also, on the observation side is a cemented lens consisting of a lens with positive refractive power and a lens with negative refractive power, and lens element N is located, which has the strongest negative refractive power within the objective optical system о. As the refractive power of a lens increases, it generates significant aberrations, but by using a cemented lens with a difference in refractive power between a convex lens and a concave lens, the field curvature that occurs at large apertures and high magnifications is corrected.

Furthermore, it is preferable that the eyepiece optical system e be composed of a total of seven lenses, arranged in order from the object side: a lens with negative refractive power, a lens with positive refractive power, a cemented lens of negative and positive refractive power lenses, a lens with positive refractive power, and a cemented lens of negative and positive refractive power lenses.

This results in a configuration that allows for excellent correction of lateral chromatic aberration while still providing a wide viewing angle.

Below are numerical examples 1 to 8 corresponding to examples 1 to 8, respectively.

In the surface data of each numerical example, r represents the radius of curvature of each optical surface, and d (mm) represents the axial spacing (distance on the optical axis) between the mth surface and the (m+1)th surface. Here, m is the surface number counted from the light incident side. Furthermore, nd represents the refractive index of each optical element with respect to the d-line, and vd represents the Abbe number of the optical element. Note that the Abbe number vd and partial dispersion ratio θgF of a certain material are given by the following when the refractive indices at the d-line (587.6 nm), F-line (486.1 nm), C-line (656.3 nm), and g-line (435.8 nm) of the Fraunhofer lines are Nd, NF, NC, and Ng, respectively:
νd=(Nd-1)/(NF-NC)
θgF=(Ng-NF)/(NF-NC)
It is expressed as:

In each numerical example, d, focal length (mm), and half angle of view ω (°) are all values when the observation optical system of each example is focused on an object at infinity. "Total lens length" is the distance on the optical axis from the frontmost lens surface (the lens surface closest to the object) of the optical system to the pupil plane. "Lens group" is not limited to cases where it is composed of multiple lenses, but also includes cases where it is composed of a single lens. In each numerical example, signs are negative toward the object side and positive toward the observation side. In addition, the outer diameter φо of the lens closest to the object in the objective optical system о and the outer diameter φp of the lens closest to the object in the image-inverting optical system z are set to values 1 mm larger than the effective diameter in each numerical example.

[Numerical Example 1]
Unit: mm

Surface data Surface number rd nd νd Effective diameter θgF
1 63.554 8.90 1.49700 81.5 50.74 0.5375
2 -189.264 1.03 50.13
3 60.643 10.17 1.49700 81.5 45.60 0.5375
4 -76.505 1.85 1.63930 44.9 43.86
5 72.757 10.22 39.62
6 42.150 3.60 1.51633 64.1 34.16
7 96.699 5.00 33.27
8 -222.350 3.20 2.00100 29.1 30.94
9 -60.008 1.00 1.65100 56.2 30.42
10 33.188 17.23 27.56
11 ∞ 95.30 1.65844 50.9 24.50
12 ∞ 17.50 24.50
13 ∞ 40.50 1.65844 50.9 24.50
14 ∞ 10.35 24.50
15 -12.588 1.00 1.71999 50.2 11.10
16 47.949 3.29 12.16
17 -19.902 4.35 1.49700 81.5 13.77
18 -9.760 4.50 15.38
19 -30.964 1.30 1.84666 23.8 17.98
20 21.680 11.40 1.69680 55.5 20.87
21 -23.806 0.20 24.76
22 127.646 8.65 1.60300 65.4 26.69
23 -24.573 0.20 27.40
24 16.858 1.40 1.92286 18.9 22.44
25 12.049 7.85 1.74100 52.6 19.86
26 28.770 13.00 16.23
Hitomi ∞

Various data magnification 24.99
Objective angle of view: 1.06
Total length (to the eye) 283.00
Pupil φ2.03
Eye relief 13.00
Eyepiece viewing angle 2ω 52.0°

Zoom lens group data group Starting surface Focal length Lens length Front principal point position Rear principal point position
1 1 234.68 44.98 -123.52 -103.17
2 11 ∞ 153.30 49.69 -49.69
3 15 9.39 57.14 13.95 -8.14

Single lens data lens Initial surface Focal length
1 1 96.86
2 3 69.78
3 4 -58.05
4 6 141.53
5 8 81.31
6 9 -32.69
7 11 0.00
8 13 0.00
9 15 -13.75
10 17 33.73
11 19 -14.89
12 20 18.15
13 22 34.92
14 24 -53.20
15 25 23.32

[Numerical Example 2]
Unit: mm

Surface data Surface number rd nd νd Effective diameter θgF
1 67.303 8.45 1.49700 81.5 50.05 0.5375
2 -156.530 8.79 49.62
3 69.742 8.46 1.49700 81.5 41.55 0.5375
4 -68.105 1.85 1.67790 55.3 40.21
5 86.767 10.22 37.15
6 63.993 2.92 1.49700 81.5 32.54
7 307.890 6.13 31.96
8 -157.519 1.00 1.70154 41.2 28.56
9 23.559 3.62 1.90366 31.3 26.81
10 44.139 10.07 26.23
11 ∞ 95.31 1.65844 50.9 24.50
12 ∞ 17.50 24.50
13 ∞ 40.50 1.65844 50.9 24.50
14 ∞ 9.36 24.50
15 -12.588 1.00 1.71999 50.2 11.68
16 2041.523 5.17 12.56
17 -10.366 3.84 1.49700 81.5 14.10
18 -9.760 7.20 16.30
19 -145.498 1.30 1.84666 23.8 21.03
20 17.269 11.42 1.69680 55.5 23.08
21 -30.574 0.20 25.55
22 45.708 8.16 1.60300 65.4 27.46
23 -29.677 0.20 27.42
24 16.296 1.40 1.92286 18.9 21.52
25 11.784 5.95 1.74100 52.6 18.96
26 20.637 13.00 15.96
Hitomi ∞

Various data magnification 25.03
Objective angle of view: 1.04
Total length (to the eye) 283.00
Pupil φ2.00
Eye relief 13.00
Eyepiece viewing angle 2ω 52.0°

Zoom lens group data group Starting surface Focal length Lens length Front principal point position Rear principal point position
1 1 235.52 51.43 -133.29 -111.04
2 11 ∞ 153.31 49.69 -49.69
3 15 9.42 58.84 15.04 -7.56

Single lens data lens Initial surface Focal length
1 1 95.90
2 3 70.77
3 4 -56.02
4 6 161.90
5 8 -29.15
6 9 51.61
7 11 0.00
8 13 0.00
9 15 -17.37
10 17 108.24
11 19 -18.17
12 20 17.56
13 22 31.11
14 24 -54.19
15 25 28.83

[Numerical Example 3]
Unit: mm

Surface data Surface number rd nd νd Effective diameter θgF
1 54.046 9.33 1.49700 81.5 51.05 0.5375
2 -261.352 7.51 50.46
3 53.561 9.00 1.49700 81.5 42.10 0.5375
4 -76.778 1.85 1.62041 60.3 40.72
5 82.655 10.48 36.75
6 48.340 1.81 1.49700 81.5 29.43
7 68.778 8.26 28.74
8 -122.670 1.00 1.73800 32.3 23.84
9 19.731 3.27 1.85478 24.8 22.13
10 33.328 9.00 21.47
11 ∞ 95.29 1.65844 50.9 24.50
12 ∞ 17.50 24.50
13 ∞ 40.50 1.65844 50.9 24.50
14 ∞ 10.00 24.50
15 -12.588 1.00 1.71999 50.2 13.18
16 -39.842 3.38 14.19
17 -12.617 3.46 1.49700 81.5 15.00
18 -9.760 15.08 16.27
19 -30.187 1.30 1.84666 23.8 18.56
20 21.653 9.80 1.69680 55.5 20.85
21 -19.217 0.20 22.83
22 36.132 4.26 1.60300 65.4 23.00
23 -76.534 0.20 22.64
24 16.322 1.40 1.92286 18.9 20.04
25 11.721 5.13 1.74100 52.6 17.90
26 31.615 13.00 16.09
Hitomi ∞

Various data magnification 30.03
Objective angle of view: 0.93
Total length (to the eye) 283.00
Pupil φ1.70
Eye relief 13.00
Eyepiece viewing angle 2ω 52.0°

Zoom lens group data group Starting surface Focal length Lens length Front principal point position Rear principal point position
1 1 300.00 52.50 -307.96 -172.62
2 11 ∞ 153.29 49.69 -49.69
3 15 10.00 58.21 18.92 -8.80

Single lens data lens Initial surface Focal length
1 1 91.00
2 3 64.97
3 4 -63.87
4 6 317.98
5 8 -22.96
6 9 50.93
7 11 0.00
8 13 0.00
9 15 -25.96
10 17 61.86
11 19 -14.72
12 20 16.21
13 22 41.29
14 24 -52.77
15 25 22.65

[Numerical Example 4]
Unit: mm

Surface data Surface number rd nd νd Effective diameter θgF
1 52.739 10.92 1.49700 81.5 52.49 0.5375
2 -207.552 3.16 51.58
3 49.592 10.30 1.49700 81.5 44.00 0.5375
4 -74.964 1.85 1.62041 60.3 42.23
5 86.219 10.06 37.38
6 51.401 1.60 1.49700 81.5 29.03
7 67.864 5.21 28.30
8 -147.233 1.00 1.73800 32.3 25.52
9 17.237 3.85 1.85478 24.8 23.16
10 28.904 5.00 22.38
11 ∞ 95.29 1.65844 50.9 24.50
12 ∞ 17.50 24.50
13 ∞ 40.50 1.65844 50.9 24.50
14 ∞ 23.15 24.50
15 -12.588 1.00 1.71999 50.2 12.39
16 -73.357 2.87 13.48
17 -15.796 4.17 1.49700 81.5 14.46
18 -9.760 7.26 15.90
19 -48.972 1.30 1.84666 23.8 17.67
20 15.583 10.53 1.69680 55.5 19.39
21 -28.768 0.20 22.00
22 69.930 4.49 1.60300 65.4 23.09
23 -35.001 0.20 23.20
24 15.793 1.40 1.92286 18.9 21.19
25 11.153 7.20 1.74100 52.6 18.81
26 51.488 13.00 16.63
Hitomi ∞

Various data magnification 29.99
Objective angle of view: 0.93
Total length (to the eye) 283.00
Pupil φ1.75
Eye relief 13.00
Eyepiece viewing angle 2ω 52.0°

Zoom lens group data group Starting surface Focal length Lens length Front principal point position Rear principal point position
1 1 300.00 47.94 -294.08 -166.82
2 11 ∞ 153.29 49.69 -49.69
3 15 10.00 53.62 15.63 -10.74

Single lens data lens Initial surface Focal length
1 1 85.81
2 3 61.75
3 4 -64.35
4 6 412.99
5 8 -20.86
6 9 43.37
7 11 0.00
8 13 0.00
9 15 -21.25
10 17 41.81
11 19 -13.83
12 20 16.07
13 22 39.32
14 24 -48.11
15 25 17.86

[Numerical Example 5]
Unit: mm

Surface data Surface number rd nd νd Effective diameter θgF
1 55.905 9.32 1.49700 81.5 51.10 0.5375
2 -217.393 4.28 50.50
3 48.180 11.00 1.49700 81.5 43.43 0.5375
4 -78.534 1.85 1.62041 60.3 41.08
5 65.982 10.96 36.51
6 45.418 2.22 1.49700 81.5 29.20
7 79.463 5.70 28.46
8 -215.326 1.00 1.73800 32.3 25.02
9 16.401 3.67 1.85478 24.8 22.64
10 27.320 5.00 21.94
11 ∞ 95.29 1.65844 50.9 24.50
12 ∞ 17.50 24.50
13 ∞ 40.50 1.65844 50.9 24.50
14 ∞ 21.36 24.50
15 -12.588 1.00 1.71999 50.2 12.43
16 -320.722 4.30 13.64
17 -12.399 5.00 1.49700 81.5 15.10
18 -9.760 7.81 17.40
19 -5440.839 1.30 1.84666 23.8 21.12
20 17.769 7.61 1.69680 55.5 22.06
21 -53.887 0.20 22.98
22 40.432 5.81 1.60300 65.4 24.00
23 -36.880 0.20 23.91
24 15.405 1.40 1.92286 18.9 20.66
25 11.158 5.72 1.74100 52.6 18.30
26 29.471 13.00 16.32
Hitomi ∞

Various data Magnification 30.00
Objective angle of view: 0.91
Total length (to the eye) 283.00
Pupil φ1.70
Eye relief 13.00
Eyepiece viewing angle 2ω 52.0°

Zoom lens group data group Starting surface Focal length Lens length Front principal point position Rear principal point position
1 1 300.00 50.00 -301.03 -169.41
2 11 ∞ 153.29 49.69 -49.69
3 15 10.00 53.35 14.84 -9.35

Single lens data lens Initial surface Focal length
1 1 90.50
2 3 61.86
3 4 -57.51
4 6 208.78
5 8 -20.61
6 9 41.57
7 11 0.00
8 13 0.00
9 15 -18.22
10 17 56.64
11 19 -20.92
12 20 20.05
13 22 32.92
14 24 -52.10
15 25 21.39

[Numerical Example 6]
Unit: mm

Surface data Surface number rd nd νd Effective diameter θgF
1 55.139 9.26 1.49700 81.5 51.41 0.5375
2 -268.283 2.76 50.87
3 54.444 10.26 1.43875 94.7 45.60 0.5340
4 -87.531 1.85 1.59551 39.2 43.92
5 93.347 15.50 40.18
6 43.806 1.72 1.61800 63.3 30.38
7 55.235 5.06 29.69
8 -159.647 3.39 1.85478 24.8 27.95
9 -38.490 1.00 1.72000 46.0 27.53
10 32.248 5.00 25.23
11 -2243.339 2.00 1.89286 20.4 25.12
12 -308.224 5.00 25.08
13 ∞ 101.15 1.65844 50.9 24.50
14 ∞ 17.50 24.50
15 ∞ 40.50 1.65844 50.9 24.50
16 ∞ 13.59 24.50
17 -12.588 1.00 1.71999 50.2 11.76
18 -263.163 1.52 12.63
19 -15.580 3.24 1.49700 81.5 12.77
20 -9.760 4.50 13.95
21 -14.946 1.30 1.84666 23.8 15.05
22 23.840 9.96 1.69680 55.5 18.80
23 -15.158 0.20 21.87
24 38.407 3.71 1.60300 65.4 23.60
25 -133.788 0.20 23.48
26 18.639 1.40 1.92286 18.9 22.38
27 12.892 7.43 1.74100 52.6 20.29
28 -568.230 13.00 18.68
Hitomi ∞

Various data magnification 30.03
Objective angle of view: 0.86
Total length (to the eye) 283.00
Pupil φ1.71
Eye relief 13.00
Eyepiece viewing angle 2ω 52.0°

Zoom lens group data group Starting surface Focal length Lens length Front principal point position Rear principal point position
1 1 280.00 57.80 -226.25 -154.34
2 13 ∞ 159.15 51.46 -51.46
3 17 9.33 47.46 13.43 -7.82

Single lens data lens Initial surface Focal length
1 1 92.91
2 3 78.23
3 4 -75.57
4 6 323.95
5 8 58.58
6 9 -24.23
7 11 400.00
8 13 0.00
9 15 0.00
10 17 -18.39
11 19 44.37
12 21 -10.69
13 22 14.86
14 24 49.89
15 26 -51.30
16 27 17.11

[Numerical Example 7]
Unit: mm

Surface data Surface number rd nd νd Effective diameter θgF
1 64.112 8.20 1.49700 81.5 51.00 0.5375
2 -248.196 2.38 50.59
3 60.418 9.50 1.49700 81.5 46.43 0.5375
4 -98.167 1.85 1.60342 38.0 45.06
5 84.733 12.51 41.37
6 48.918 3.00 1.49700 81.5 34.34
7 89.711 9.99 33.45
8 -164.845 2.38 1.94594 18.0 27.75
9 -59.594 1.00 1.69350 50.8 27.39
10 36.391 5.00 25.50
11 -927.337 1.00 1.88300 40.8 25.12
12 2270.636 5.00 25.05
13 ∞ 101.18 1.65844 50.9 24.50
14 ∞ 17.50 24.50
15 ∞ 40.50 1.65844 50.9 24.50
16 ∞ 15.08 24.50
17 -12.588 1.00 1.71999 50.2 11.64
18 40.617 2.10 12.71
19 -22.346 5.70 1.49700 81.5 13.27
20 -9.760 5.04 15.63
21 -16.652 1.30 1.84666 23.8 17.69
22 -162.004 6.24 1.69680 55.5 20.32
23 -16.410 0.20 22.15
24 94.351 4.01 1.60300 65.4 23.28
25 -36.956 0.20 23.33
26 17.223 1.40 1.92286 18.9 21.29
27 11.960 6.74 1.74100 52.6 19.10
28 100.152 13.00 17.32
Hitomi ∞

Various data magnification 29.98
Objective angle of view: 0.89
Total length (to the eye) 283.00
Pupil φ1.70
Eye relief 13.00
Eyepiece viewing angle 2ω 52.0°

Zoom lens group data group Starting surface Focal length Lens length Front principal point position Rear principal point position
1 1 280.02 56.81 -228.68 -153.56
2 13 ∞ 159.18 51.47 -51.47
3 17 9.33 46.93 12.80 -7.57

Single lens data lens Initial surface Focal length
1 1 103.42
2 3 76.78
3 4 -75.08
4 6 211.30
5 8 97.60
6 9 -32.44
7 11 -745.57
8 13 0.00
9 15 0.00
10 17 -13.24
11 19 30.31
12 21 -22.01
13 22 25.75
14 24 44.55
15 26 -48.62
16 27 17.75

[Numerical Example 8]
Unit: mm

Surface data Surface number rd nd νd Effective diameter θgF
1 73.359 8.00 1.49700 81.5 51.78 0.5375
2 -202.933 0.69 51.37
3 61.525 9.40 1.49700 81.5 47.70 0.5375
4 -99.343 1.85 1.60342 38.0 46.57
5 80.506 11.18 42.57
6 51.573 3.32 1.49700 81.5 36.42
7 130.665 9.44 35.69
8 -237.936 2.58 1.92286 18.9 29.66
9 -78.869 1.00 1.55332 71.7 29.13
10 38.680 19.30 26.77
11 -86.670 1.00 1.80100 35.0 21.19
12 -1435.164 7.83 21.12
13 ∞ 71.61 1.65844 50.9 20.46
14 ∞ 17.50 20.46
15 ∞ 40.50 1.65844 50.9 20.46
16 ∞ 13.59 20.46
17 -12.588 1.00 1.71999 50.2 12.27
18 -50.415 2.41 13.15
19 -10.308 1.82 1.49700 81.5 13.35
20 -9.760 15.22 14.33
21 -26.145 1.30 1.84666 23.8 20.42
22 31.186 10.50 1.69680 55.5 24.27
23 -21.305 0.20 26.98
24 57.468 5.96 1.60300 65.4 29.56
25 -46.317 0.20 29.60
26 17.113 1.40 1.92286 18.9 26.19
27 12.032 11.20 1.74100 52.6 22.51
28 39.975 13.00 18.15
Image plane ∞

Various data magnification (up to pupil) 31.00
Objective angle of view: 0.83
Total length 283.00
Pupil φ1.67
Eye relief 13.00
Eyepiece viewing angle 2ω 52.0°

Zoom lens group data group Starting surface Focal length Lens length Front principal point position Rear principal point position
1 1 290.80 67.77 -280.45 -176.05
2 13 ∞ 129.61 42.55 -42.55
3 17 9.38 64.21 17.60 -8.94

Single lens data lens Initial surface Focal length
1 1 109.47
2 3 77.96
3 4 -73.41
4 6 169.08
5 8 126.85
6 9 -46.76
7 11 -115.19
8 13 0.00
9 15 0.00
10 17 -23.56
11 19 175.72
12 21 -16.63
13 22 19.79
14 24 43.47
15 26 -50.60
16 27 19.84

The various values in each numerical example are summarized in Table 1 below.

In the above embodiments, the present invention has been described as being applied to observation optical systems (types of optical systems that form an intermediate image within the optical system), such as binoculars and telescopes, but the present invention is not limited to observation optical systems. The present invention may also be applied to imaging optical systems that form a real image of a subject (object) on a photoelectric conversion element, i.e., optical devices such as digital still cameras, video cameras, interchangeable lenses that can be attached to camera bodies (such as single-lens reflex cameras), and mobile phone cameras. The above embodiments can be applied to a variety of optical systems that have imaging optical systems and observation optical systems.

The above describes preferred embodiments and examples of the present invention, but the present invention is not limited to these embodiments and examples, and various combinations, modifications, and variations are possible within the scope of the invention.

Objective optical system o, o1, o2
Image inversion optical system z, z1, z2
Eyepiece optical system e, e1, e2
First lens group L1
First lens element N

Claims (26)

An observation optical system having an objective optical system, an image-inverting optical system, and an eyepiece optical system, which are arranged in this order from an object side to an observation side, and in which an image formed by the objective optical system is magnified and observed by the eyepiece optical system,
the objective optical system comprises, arranged in order from an object side to an observation side, a first lens group having a positive refractive power and a first lens element having the strongest negative refractive power in the objective optical system;
Let f0 be the focal length of the objective optical system, fn be the focal length of the first lens element, L be the optical path length along the optical axis from the lens surface of the objective optical system closest to the object side to the lens surface of the eyepiece optical system closest to the observation side, l be the optical path length along the optical axis from the surface of the image-inverting optical system closest to the object side to the lens surface of the eyepiece optical system closest to the observation side , and fe be the focal length of the eyepiece optical system .
-15.00<fо/fn<-3.00
0.70<l/L<0.90
15.0<fо/fe<40.0
An observation optical system characterized by satisfying the following conditional expression: When the focal length of the first lens group is f1,
-3.00<f1/fn<-0.80
2. The viewing optical system according to claim 1, wherein the following condition is satisfied: When the distance on the optical axis from the lens surface of the objective optical system closest to the object side to the surface of the image-inverting optical system closest to the object side is d0,
3.50<fо/dо<10.00
3. The viewing optical system according to claim 1, wherein the following condition is satisfied: When the focal length of the first lens group is f1,
0.15<f1/fо<0.50
4. The viewing optical system according to claim 1, wherein the following condition is satisfied: When the outer diameter of the lens closest to the object side of the objective optical system is φo and the outer diameter of the image-inverting optical system closest to the object side is φp,
1.80<φо/φp<2.60
5. The viewing optical system according to claim 1, wherein the following condition is satisfied: the first lens element is composed of a cemented lens of a lens having a positive refractive power and a lens having a negative refractive power;
When the refractive index of the lens having the positive refractive power is np and the refractive index of the lens having the negative refractive power is nn,
0.05<np-nn<0.50
6. The viewing optical system according to claim 1, wherein the following condition is satisfied: An observation optical system having an objective optical system, an image-inverting optical system, and an eyepiece optical system, which are arranged in this order from an object side to an observation side, and in which an image formed by the objective optical system is magnified and observed by the eyepiece optical system,
the objective optical system comprises, arranged in order from an object side to an observation side, a first lens group having a positive refractive power and a first lens element having the strongest negative refractive power in the objective optical system;
the first lens element is composed of a cemented lens of a lens having a positive refractive power and a lens having a negative refractive power;
Let f0 be the focal length of the objective optical system, fn be the focal length of the first lens element, L be the optical path length along the optical axis from the lens surface of the objective optical system closest to the object side to the lens surface of the eyepiece optical system closest to the observation side, l be the optical path length along the optical axis from the surface of the image-inverting optical system closest to the object side to the lens surface of the eyepiece optical system closest to the observation side, np be the refractive index of the lens with positive refractive power, and nn be the refractive index of the lens with negative refractive power.
-15.00<fо/fn<-3.00
0.70<l/L<0.90
0.05<np-nn<0.50
An observation optical system characterized by satisfying the following conditional expression: When the radius of curvature of the lens surface of the first lens element closest to the object side is nR1 and the radius of curvature of the lens surface of the first lens element closest to the observation side is nR2,
1.00<(nR1-nR2)/(nR1+nR2)<5.00
8. The viewing optical system according to claim 1, wherein the following condition is satisfied: When the distance on the optical axis from the lens surface of the first lens element closest to the observation side to the surface of the image-inverting optical system closest to the object side is dn,
0.05<dn/dо<0.50
9. The viewing optical system according to claim 1, wherein the following condition is satisfied: 10. The viewing optical system according to claim 1, wherein the first lens group includes, in order from the object side to the viewing side, a first lens having a positive refractive power, and a cemented lens of a second lens having a positive refractive power and a third lens having a negative refractive power. An observation optical system having an objective optical system, an image-inverting optical system, and an eyepiece optical system, which are arranged in this order from an object side to an observation side, and in which an image formed by the objective optical system is magnified and observed by the eyepiece optical system,
the objective optical system comprises, arranged in order from an object side to an observation side, a first lens group having a positive refractive power and a first lens element having the strongest negative refractive power in the objective optical system;
the first lens group includes, arranged in order from the object side to the observation side, a first lens having positive refractive power, and a cemented lens of a second lens having positive refractive power and a third lens having negative refractive power;
Let f0 be the focal length of the objective optical system, fn be the focal length of the first lens element, L be the optical path length along the optical axis from the lens surface of the objective optical system closest to the object side to the lens surface of the eyepiece optical system closest to the observation side, and l be the optical path length along the optical axis from the surface of the image-inverting optical system closest to the object side to the lens surface of the eyepiece optical system closest to the observation side.
-15.00<fо/fn<-3.00
0.70<l/L<0.90
An observation optical system characterized by satisfying the following conditional expression: the first lens group includes a second lens element having a positive refractive power, the second lens element being disposed on the object side of the first lens element;
12. The viewing optical system according to claim 1, wherein the second lens element moves toward the object side during focusing. An observation optical system having an objective optical system, an image-inverting optical system, and an eyepiece optical system, which are arranged in this order from an object side to an observation side, and in which an image formed by the objective optical system is magnified and observed by the eyepiece optical system,
the objective optical system comprises, arranged in order from an object side to an observation side, a first lens group having a positive refractive power and a first lens element having the strongest negative refractive power in the objective optical system;
the first lens group includes a second lens element having a positive refractive power, the second lens element being disposed on the object side of the first lens element;
During focusing, the second lens element moves toward the object side,
Let f0 be the focal length of the objective optical system, fn be the focal length of the first lens element, L be the optical path length along the optical axis from the lens surface of the objective optical system closest to the object side to the lens surface of the eyepiece optical system closest to the observation side, and l be the optical path length along the optical axis from the surface of the image-inverting optical system closest to the object side to the lens surface of the eyepiece optical system closest to the observation side.
-15.00<fо/fn<-3.00
0.70<l/L<0.90
An observation optical system characterized by satisfying the following conditional expression: When the radius of curvature of the lens surface of the second lens element closest to the object side is fR1 and the radius of curvature of the lens surface of the second lens element closest to the observation side is fR2,
-0.90<(fR1-fR2)/(fR1+fR2)<-0.05
14. The viewing optical system according to claim 1, 2 or 13 , wherein the following condition is satisfied: When the focal length of the second lens element is ff,
0.50<fо/ff<3.00
15. The viewing optical system according to claim 12, wherein the following condition is satisfied: 15. The observation optical system according to claim 12 , wherein the second lens element has a meniscus shape convex toward the object side. 17. The observation optical system according to claim 1, wherein vibration reduction due to hand shake is performed by moving the image-inverting optical system parallel to the optical axis or tilting the image-inverting optical system. When the Abbe number of the glass material of the first lens having a positive refractive power and the second lens having a positive refractive power is νd and the partial dispersion ratio is θgF,
θgF-(-1.665×10-7・νd3+5.213×10-5・νd2-5.656×10-3・νd+0.737)>0
60.0<νd<100.0
11. The viewing optical system according to claim 10 , wherein the following condition is satisfied: 19. The observation optical system according to claim 1, wherein the objective optical system is composed of the first lens group and the first lens element, arranged in order from the object side to the observation side. An observation optical system according to any one of claims 1 to 19, characterized in that the objective optical system is composed of the first lens group, the first lens element, and a lens with positive or negative refractive power, arranged in order from the object side to the observation side. 21. The observation optical system according to claim 1, wherein the first lens group is composed of a total of four lenses, arranged in order from the object side to the observation side: a lens with positive refractive power, a cemented lens of a lens with positive refractive power and a lens with negative refractive power, and a lens with positive refractive power. 22. The observation optical system according to claim 1, wherein the eyepiece optical system is composed of a total of seven lenses, arranged in order from the object side to the observation side: a lens with negative refractive power, a lens with positive refractive power, a cemented lens of a lens with negative refractive power and a lens with positive refractive power, a lens with positive refractive power, and a cemented lens of a lens with negative refractive power and a lens with positive refractive power. An observation optical system having an objective optical system, an image-inverting optical system, and an eyepiece optical system, which are arranged in this order from an object side to an observation side, and in which an image formed by the objective optical system is magnified and observed by the eyepiece optical system,
the objective optical system comprises, arranged in order from an object side to an observation side, a first lens group having a positive refractive power and a first lens element having the strongest negative refractive power in the objective optical system;
the eyepiece optical system is composed of seven lenses, arranged in this order from the object side to the observation side, including a lens with negative refractive power, a lens with positive refractive power, a cemented lens of a lens with negative refractive power and a lens with positive refractive power, a lens with positive refractive power, and a cemented lens of a lens with negative refractive power and a lens with positive refractive power ;
Let f0 be the focal length of the objective optical system, fn be the focal length of the first lens element, L be the optical path length along the optical axis from the lens surface of the objective optical system closest to the object side to the lens surface of the eyepiece optical system closest to the observation side, and l be the optical path length along the optical axis from the surface of the image-inverting optical system closest to the object side to the lens surface of the eyepiece optical system closest to the observation side.
-15.00<fо/fn<-3.00
0.70<l/L<0.90
An observation optical system characterized by satisfying the following conditional expression: 23. The observation optical system according to claim 1, wherein the observation optical system is composed of the objective optical system, the image inverting optical system, a prism for adjusting an eye distance, and the eyepiece optical system. An observation device comprising two observation optical systems, a first observation optical system as the observation optical system according to any one of claims 1 to 24 , and a second observation optical system as the observation optical system. 26. The observation device according to claim 25 , wherein the two observation optical systems are arranged in parallel.