Eyepiece optical system, optical apparatus, and observation method

Abstract

An eyepiece optical system (EL) has a first positive lens (Lp1) having positive refractive power and a second positive lens (Lp2) having positive refractive power, and satisfies the following conditional expressions.　1.700<Np1<2.050 1.700<Np2<2.050 (wherein, Np1 is the refractive index of the first positive lens (Lp1) with respect to a line d, and Np2 is the refractive index of the second positive lens (Lp2) with respect to the line d)

Description

Eyepiece optical system, optical instrument, and observation method

[0001] The present invention relates to an eyepiece optical system suitable for an electronic viewfinder (so-called EVF) or the like, for observing an image displayed on an image display element.

[0002] An eyepiece optical system has been proposed that allows an image displayed on an image display element to be observed at high magnification (see, for example, Patent Document 1). However, with such an eyepiece optical system, it is difficult to correct various aberrations, particularly astigmatism and distortion, to achieve good optical performance.

[0003] JP 2013-88632 A

[0004] The eyepiece optical system according to a first aspect of the present invention has a first positive lens having positive refractive power and a second positive lens having positive refractive power, and satisfies the following conditional expressions: 1.700<Np1<2.050 1.700<Np2<2.050, where Np1 is the refractive index of the first positive lens for the d-line, and Np2 is the refractive index of the second positive lens for the d-line.

[0005] The eyepiece optical system according to the second aspect of the present invention has at least five lenses and satisfies the following condition: 0.400<h / fe<0.500, where fe is the composite focal length of the eyepiece optical system, and h is the maximum object height of the object to be observed through the eyepiece optical system.

[0006] The third eyepiece optical system according to the present invention is an eyepiece optical system for observing an image displayed on an image display device, and has at least five lenses.

[0007] The optical instrument according to the present invention comprises an objective lens, an imaging element for capturing an image formed by the objective lens, an image display element for displaying the image captured by the imaging element, and an eyepiece optical system for observing the image displayed on the image display element, the eyepiece optical system being any of the eyepiece optical systems described above.

[0008] In the observation method according to the present invention, the object to be observed is observed through any one of the above-described eyepiece optical systems.

[0009] 1 is a diagram showing the configuration of an eyepiece optical system according to Example 1. FIG. 2 is a diagram showing the diopter of the eyepiece optical system according to Example 1.-1 ]. It is a diagram showing the configuration of the eyepiece optical system according to the second example. It is a diagram showing various aberrations when the diopter of the eyepiece optical system according to the second example is -1 [m -1 ]. It is a diagram showing the configuration of the eyepiece optical system according to the third example. It is a diagram showing various aberrations when the diopter of the eyepiece optical system according to the third example is -1 [m -1 ]. It is a diagram showing the configuration of the eyepiece optical system according to the fourth example. It is a diagram showing various aberrations when the diopter of the eyepiece optical system according to the fourth example is -1 [m -1 ]. It is a diagram showing the configuration of the eyepiece optical system according to the fifth example. It is a diagram showing various aberrations when the diopter of the eyepiece optical system according to the fifth example is -1 [m -1 ]. FIG. 6 is a diagram showing the configuration of the eyepiece optical system according to Example 6. FIG. 7 is a diagram showing various aberrations when the diopter of the eyepiece optical system according to Example 6 is -1 [m -1 ]. It is a diagram showing the configuration of the eyepiece optical system according to Example 7. It is a diagram showing various aberrations when the diopter of the eyepiece optical system according to Example 7 is -1 [m -1 10 is a cross-sectional view of a digital camera.

[0010] Preferred embodiments of the present invention will now be described. First, a digital camera CAM (optical apparatus) is shown in FIG. 15 as an optical apparatus equipped with an eyepiece optical system EL according to each embodiment. The digital camera CAM comprises an objective lens OL, an image sensor C such as a CCD or CMOS, and an electronic viewfinder EVF. The electronic viewfinder EVF comprises an image display element (observation object) Ob such as a liquid crystal display element, and an eyepiece optical system EL for magnifying and observing an image displayed on the image display element Ob.

[0011] In the digital camera CAM configured as described above, light from an object (subject) (not shown) is collected by the objective lens OL and focused on the image sensor C to form an image of the subject. The image of the subject focused on the image sensor C is then captured by the image sensor C, and the image of the subject captured by the image sensor C is displayed on the image display device Ob. By positioning his or her eye at the eyepoint EP, the photographer can observe a magnified image of the object (subject) formed by the objective lens OL via the eyepiece optical system EL.

[0012] Furthermore, when the photographer presses the release button (not shown), the image captured by the image sensor C (i.e., the image corresponding to the image displayed on the image display device Ob as viewed through the eyepiece optical system EL) is recorded in a memory (not shown) as an image of the object (subject). In this way, the photographer can photograph the object (subject) using the digital camera CAM. The eyepiece optical system EL shown in FIG. 15 is a schematic representation of the eyepiece optical system provided in the digital camera CAM, and the lens configuration of the eyepiece optical system EL is not limited to this configuration.

[0013] Next, we will explain the eyepiece optical system according to the first embodiment. As shown in Figure 1, the eyepiece optical system EL (EL1) as an example of the eyepiece optical system EL according to the first embodiment has a first positive lens Lp1 having positive refractive power and a second positive lens Lp2 having positive refractive power.

[0014] With the above-described configuration, the eyepiece optical system EL according to the first embodiment satisfies the following conditional expressions (1) and (2): 1.700<Np1<2.050 (1) 1.700<Np2<2.050 (2) where Np1 is the refractive index of the first positive lens Lp1 for the d-line, and Np2 is the refractive index of the second positive lens Lp2 for the d-line.

[0015] According to the first embodiment, it is possible to obtain an eyepiece optical system having good optical performance in which various aberrations, particularly astigmatism and distortion, are corrected, and an optical apparatus equipped with this eyepiece optical system. The variable magnification optical system ZL according to the first embodiment may be the eyepiece optical system EL (EL2) shown in Fig. 3, the eyepiece optical system EL (EL3) shown in Fig. 5, the eyepiece optical system EL (EL4) shown in Fig. 7, the eyepiece optical system EL (EL5) shown in Fig. 9, the eyepiece optical system EL (EL6) shown in Fig. 11, or the eyepiece optical system EL (EL7) shown in Fig. 13.

[0016] Conditional expression (1) defines the refractive index of the first positive lens Lp1 for the d-line within an appropriate range. When the positive lens Lp1 satisfies conditional expression (1), astigmatism can be corrected well.

[0017] If the corresponding value of conditional expression (1) exceeds the upper limit, the refractive index of the positive lens Lp1 becomes large, the Petzval sum deteriorates, and it becomes difficult to correct astigmatism. By setting the upper limit of conditional expression (1) to 1.960 or even 1.890, the effect of this embodiment can be further ensured.

[0018] If the corresponding value of conditional expression (1) is below the lower limit, the refractive index of the positive lens Lp1 becomes small, the Petzval sum deteriorates, and it becomes difficult to correct astigmatism. By setting the lower limit of conditional expression (1) to 1.750 or even 1.810, the effect of this embodiment can be further ensured.

[0019] Conditional expression (2) defines the refractive index of the second positive lens Lp2 for the d-line within an appropriate range. When the positive lens Lp2 satisfies conditional expression (2), astigmatism can be corrected well.

[0020] If the corresponding value of conditional expression (2) exceeds the upper limit, the refractive index of the positive lens Lp2 becomes large, the Petzval sum deteriorates, and it becomes difficult to correct astigmatism. By setting the upper limit of conditional expression (2) to 1.960 or even 1.890, the effect of this embodiment can be further ensured.

[0021] If the corresponding value of conditional expression (2) is below the lower limit, the refractive index of the positive lens Lp2 becomes small, the Petzval sum deteriorates, and it becomes difficult to correct astigmatism. By setting the lower limit of conditional expression (2) to 1.750 or even 1.810, the effect of this embodiment can be further ensured.

[0022] In the eyepiece optical system EL according to the first embodiment, it is desirable that the first positive lens Lp1 has the strongest positive refractive power in the eyepiece optical system EL and satisfies the following conditional expression (3): 0.90<Np2 / Np1<1.10 (3).

[0023] Conditional expression (3) defines an appropriate relationship between the refractive index of the second positive lens Lp2 for the d-line and the refractive index of the first positive lens Lp1 for the d-line. By satisfying conditional expression (3), astigmatism can be effectively corrected.

[0024] If the value corresponding to conditional expression (3) exceeds the upper limit, the refractive index of the first positive lens Lp1, which has the strongest positive refractive power relative to the second positive lens, for the d-line becomes too small, deteriorating the Petzval sum and making it difficult to correct astigmatism. By setting the upper limit of conditional expression (3) to 1.05 or even 1.01, the effect of this embodiment can be made even more certain.

[0025] If the corresponding value of conditional expression (3) is below the lower limit, the refractive index of the first positive lens Lp1 at the d-line becomes too large relative to the second positive lens, deteriorating the Petzval sum and making it difficult to correct astigmatism. By setting the lower limit of conditional expression (3) to 0.92, 0.94, 0.95, or even 0.96, the effect of this embodiment can be made more certain.

[0026] In the eyepiece optical system EL according to the first embodiment, it is preferable that the first positive lens Lp1 has the strongest positive refractive power in the eyepiece optical system EL and satisfies the following conditional expression (4): 0.70<fLp1 / fe<1.30 (4), where fLp1 is the focal length of the first positive lens Lp1, and fe is the combined focal length of the eyepiece optical system EL.

[0027] Condition (4) defines an appropriate relationship between the focal length of the entire eyepiece optical system EL and the focal length of the first positive lens Lp1. By satisfying condition (4), it is possible to effectively correct curvature of field.

[0028] If the value corresponding to conditional expression (4) exceeds the upper limit, the refractive power of the first positive lens Lp1 becomes weak, the Petzval sum deteriorates, and it becomes difficult to correct the curvature of field. By setting the upper limit of conditional expression (4) to 1.28, 1.24, 1.22, 1.20, or even 1.10, the effect of this embodiment can be made more certain.

[0029] If the corresponding value of conditional expression (4) is below the lower limit, the refractive power of the first positive lens Lp1 becomes strong, the Petzval sum deteriorates, and it becomes difficult to correct the curvature of field. By setting the lower limit of conditional expression (4) to 0.720, 0.740, 0.750, 0.800, or even 0.900, the effect of this embodiment can be made more certain.

[0030] In the eyepiece optical system EL according to the first embodiment, it is preferable that the second positive lens Lp2 has the second strongest positive refractive power in the eyepiece optical system EL and satisfies the following conditional expression (5): 0.90<fLp2 / fe<1.70 (5), where fLp2 is the focal length of the second positive lens Lp2, and fe is the combined focal length of the eyepiece optical system EL.

[0031] Condition (5) defines an appropriate relationship between the focal length of the entire eyepiece optical system EL and the focal length of the second positive lens Lp2. By satisfying condition (5), it is possible to effectively correct curvature of field.

[0032] If the corresponding value of conditional expression (5) exceeds the upper limit, the refractive power of the second positive lens Lp2 becomes weak, the Petzval sum deteriorates, and it becomes difficult to correct the curvature of field. By setting the upper limit of conditional expression (5) to 1.68, 1.58, 1.55, 1.35, or even 1.30, the effect of this embodiment can be made more certain.

[0033] If the corresponding value of conditional expression (5) is below the lower limit, the refractive power of the second positive lens Lp2 becomes strong, the Petzval sum deteriorates, and it becomes difficult to correct the curvature of field. By setting the lower limit of conditional expression (5) to 0.95, 1.00, or even 1.10, the effect of this embodiment can be made more certain.

[0034] The eyepiece optical system EL according to the first embodiment preferably has a first negative lens Ln1 that has the strongest negative refractive power in the eyepiece optical system EL, and satisfies the following conditional expressions (6) and (7): 1.500<Nn1<1.700 (6) 16.000<νn1<36.000 (7) where Nn1 is the refractive index of the first negative lens Ln1 with respect to the d line, and νn1 is the Abbe number of the first negative lens Ln1 with respect to the d line.

[0035] Conditional expression (6) defines the refractive index for the d-line of the first negative lens Ln1, which has the strongest negative refractive power in the eyepiece optical system EL, within an appropriate range. When the negative lens Ln1 satisfies conditional expression (6), astigmatism can be effectively corrected.

[0036] If the corresponding value of conditional expression (6) exceeds the upper limit, the refractive index of the negative lens Ln1 becomes large, the Petzval sum deteriorates, and it becomes difficult to correct astigmatism. By setting the upper limit of conditional expression (6) to 1.650 or even 1.640, the effect of this embodiment can be further ensured.

[0037] If the corresponding value of conditional expression (6) is below the lower limit, the refractive index of the negative lens Ln1 becomes small, the Petzval sum deteriorates, and it becomes difficult to correct astigmatism. By setting the lower limit of conditional expression (6) to 1.530, 1.550, or even 1.600, the effect of this embodiment can be further ensured.

[0038] Conditional expression (7) defines the Abbe number of the first negative lens Ln1, which has the strongest negative refractive power in the eyepiece optical system EL, within an appropriate range. When the Abbe number of the negative lens Ln1 satisfies conditional expression (7), chromatic aberration can be effectively corrected.

[0039] If the corresponding value of conditional expression (7) exceeds the upper limit, the dispersion by the negative lens Ln1 becomes small, and the correction of chromatic aberration becomes insufficient, which is undesirable. By setting the upper limit of conditional expression (7) to 30,000, or even 25,000, the effect of this embodiment can be made more certain.

[0040] If the corresponding value of conditional expression (7) falls below the lower limit, dispersion by the negative lens Ln1 increases, resulting in excessive correction of chromatic aberration, which is undesirable. By setting the lower limit of conditional expression (7) to 18,000 or even 20,000, the effect of this embodiment can be made even more certain.

[0041] It is preferable that the eyepiece optical system EL according to the first embodiment has a second negative lens Ln2 having the second strongest negative refractive power in the eyepiece optical system EL, and that the following conditional expression (8) be satisfied: 1.500<Nn2<1.700 (8), where Nn2 is the refractive index of the second negative lens Ln2 at the d-line.

[0042] Conditional expression (8) defines the refractive index for the d-line of the second negative lens Ln2, which has the second strongest refractive power in the eyepiece optical system EL, within an appropriate range. When the negative lens Ln2 satisfies conditional expression (8), astigmatism can be effectively corrected.

[0043] If the corresponding value of conditional expression (8) exceeds the upper limit, the refractive index of the negative lens Ln2 becomes large, the Petzval sum deteriorates, and it becomes difficult to correct astigmatism. By setting the upper limit of conditional expression (8) to 1.650 or even 1.640, the effect of this embodiment can be further ensured.

[0044] If the corresponding value of conditional expression (8) is below the lower limit, the refractive index of the negative lens Ln2 becomes small, the Petzval sum deteriorates, and it becomes difficult to correct astigmatism. By setting the lower limit of conditional expression (8) to 1.530, 1.550, or even 1.600, the effect of this embodiment can be further ensured.

[0045] In the eyepiece optical system EL according to the first embodiment, it is preferable to have the first negative lens Ln1 having the strongest negative refractive power and to satisfy the following conditional expression (9): 8.000<νp1−νn1<35.000 (9), where νp1 is the Abbe number of the first positive lens Lp1 with reference to the d-line, and νn1 is the Abbe number of the first negative lens Ln1 with reference to the d-line.

[0046] Conditional expression (9) defines the difference in Abbe number between the first positive lens Lp1 and the first negative lens Ln1 within an appropriate range. By satisfying conditional expression (9), chromatic aberration can be corrected satisfactorily.

[0047] If the value corresponding to conditional expression (9) exceeds the upper limit, the dispersion of the negative lens Ln1 becomes large relative to the first positive lens Lp1, which is undesirable because chromatic aberration becomes overcorrected. By setting the upper limit of conditional expression (9) to 30,000, or even 25,000, the effect of this embodiment can be made even more certain.

[0048] If the corresponding value of conditional expression (9) is below the lower limit, the dispersion of the negative lens Ln1 becomes small relative to the first positive lens Lp1, and correction of chromatic aberration becomes insufficient, which is undesirable. By setting the lower limit of conditional expression (9) to 10,000, 12,000, 15,000, or even 20,000, the effect of this embodiment can be made more certain.

[0049] It is preferable that the eyepiece optical system EL according to the first embodiment has the first negative lens Ln1 having the strongest negative refractive power and satisfies the following conditional expression (10): 8.000<νp2−νn1<35.000 (10), where νp2 is the Abbe number of the second positive lens Lp2 with reference to the d-line, and νn1 is the Abbe number of the first negative lens Ln1 with reference to the d-line.

[0050] Conditional expression (10) defines the difference in Abbe number between the second positive lens Lp2 and the first negative lens Ln1 within an appropriate range. By satisfying conditional expression (10), chromatic aberration can be corrected satisfactorily.

[0051] If the corresponding value of conditional expression (10) exceeds the upper limit, the dispersion of the negative lens Ln1 becomes large relative to the second positive lens Lp2, which is undesirable because chromatic aberration becomes overcorrected. By setting the upper limit of conditional expression (10) to 30,000, or even 25,000, the effect of this embodiment can be made even more certain.

[0052] If the corresponding value of conditional expression (10) is below the lower limit, the dispersion of the negative lens Ln1 becomes small relative to the second positive lens Lp2, and correction of chromatic aberration becomes insufficient, which is undesirable. By setting the lower limit of conditional expression (10) to 10,000, 12,000, 15,000, or even 20,000, the effect of this embodiment can be made more certain.

[0053] In the eyepiece optical system EL according to the first embodiment, it is preferable to satisfy the following conditional expression (11): 0.400<h / fe<0.500 (11) where fe is the combined focal length of the eyepiece optical system EL, and h is the maximum object height of the object Ob to be observed in the eyepiece optical system EL.

[0054] Condition (11) defines the size of the image obtained by the eyepiece optical system EL based on the maximum object height of the observed object Ob relative to the overall focal length of the eyepiece optical system EL. By satisfying condition (11), various aberrations can be effectively corrected even if the angle of view is large.

[0055] If the corresponding value of conditional expression (11) exceeds the upper limit, the field of view becomes too large, making it difficult to correct off-axis aberrations, which is undesirable. By setting the upper limit of conditional expression (11) to 0.480, 0.470, 0.460, or even 0.450, the effect of this embodiment can be made more certain.

[0056] If the corresponding value of conditional expression (11) falls below the lower limit, the magnification of the eyepiece optical system EL becomes high, making it difficult to correct various aberrations. By setting the lower limit of conditional expression (11) to 0.420, 0.430, or even 0.440, the effect of this embodiment can be made even more certain.

[0057] The eyepiece optical system EL according to the first embodiment preferably has at least one lens having an aspherical surface formed on a lens surface that satisfies the following condition (12): 0.000≦D aspe / ΣD<0.200 (12) where D aspe is the distance on the optical axis from the aspherical surface closest to the eyepoint to the lens surface of the eyepiece optical system EL closest to the eyepoint, and ΣD is the distance on the optical axis from the lens surface closest to the object to be observed Ob to the lens surface closest to the eyepoint EP.

[0058] Conditional expression (12) defines within an appropriate range the ratio of the distance on the optical axis from the aspherical surface closest to the eyepoint EP to the lens surface closest to the eyepoint EP to the distance on the optical axis from the lens surface closest to the object to be observed Ob to the lens surface closest to the eyepoint EP. By satisfying conditional expression (12), spherical aberration and coma occurring on the eyepoint EP side can be effectively corrected.

[0059] If the corresponding value of conditional expression (12) exceeds the upper limit, the position of the aspherical surface located closest to the eyepoint EP will be farther away from the eyepoint EP, making it difficult to correct spherical aberration and coma that occur on the eyepoint EP side. By setting the upper limit of conditional expression (12) to 0.190 or even 0.170, the effect of this embodiment can be further ensured. The lower limit of conditional expression (12) represents the lens surface closest to the eyepoint EP.

[0060] The eyepiece optical system EL according to the first embodiment preferably has at least one lens having an aspherical surface formed on a lens surface that satisfies the following conditional expression (13): 0.000≦Daspo / ΣD<0.200 (13) where Daspo is the distance on the optical axis from the lens surface of the eyepiece optical system EL closest to the object to be observed Ob to the aspherical surface closest to the object to be observed Ob of the aspherical surfaces, and ΣD is the distance on the optical axis from the lens surface closest to the object to be observed Ob to the lens surface closest to the eyepoint EP.

[0061] Conditional expression (13) defines within an appropriate range the ratio of the axial distance from the lens surface closest to the object under observation Ob to the aspherical surface closest to the object under observation Ob, to the axial distance from the lens surface closest to the object under observation Ob to the lens surface closest to the eyepoint EP. Satisfying conditional expression (13) enables good correction of distortion occurring on the side of the eyepiece optical system EL closest to the object under observation Ob.

[0062] If the corresponding value of conditional expression (13) exceeds the upper limit, the position of the aspherical surface arranged closest to the observed object Ob will be farther away from the observed object Ob, making it difficult to correct distortion occurring on the observed object Ob side. By setting the upper limit of conditional expression (13) to 0.190 or even 0.170, the effect of this embodiment can be further ensured. The lower limit of conditional expression (13), 0.000, represents the lens surface closest to the observed object Ob.

[0063] The eyepiece optical system EL according to the first embodiment preferably has at least one lens La having an aspherical lens surface with an inflection point on the aspherical surface where the radius of curvature reverses from positive to negative or from negative to positive, and satisfies the following conditional expression (14): 0.20<y / Ry<0.85 (14), where y is the distance between the optical axis of the lens La and the inflection point in a direction perpendicular to the optical axis, and Ry is the radius of the lens La.

[0064] Conditional expression (14) defines an appropriate range for the ratio of the distance between the optical axis and the position of the inflection point on lens La in a direction perpendicular to the optical axis to the radius of lens La. By satisfying conditional expression (14), an inflection point is provided at the periphery of the optical axis within the aperture of lens La, thereby enabling excellent correction of distortion. The inflection point is the position at which the radius of curvature reverses, and the radius of curvature reverses from positive to negative or from negative to positive across this position. It is desirable that the lens having the aspherical surface closest to the object under observation Ob be configured as the lens La having the inflection point. Such a configuration enables excellent correction of distortion. Furthermore, by configuring lens La as a lens having positive refractive power paraxially and having an inflection point on the periphery, telecentricity on the side of the object under observation Ob can be improved.

[0065] If the corresponding value of conditional expression (14) exceeds the upper limit, distortion at intermediate image heights will undesirably worsen. By setting the upper limit of conditional expression (14) to 0.700, or even 0.500, the effect of this embodiment can be made even more certain.

[0066] If the corresponding value of conditional expression (14) falls below the lower limit, the curvature of field will undesirably worsen. By setting the lower limit of conditional expression (14) to 0.250 or even 0.300, the effect of this embodiment can be made more certain.

[0067] The eyepiece optical system EL according to the first embodiment is preferably configured with at least five lenses. This configuration allows for good correction of various aberrations. If the number of lenses were four or less, the refractive power of each lens would be too strong, making aberration correction difficult.

[0068] In the eyepiece optical system EL according to the first embodiment, it is preferable that the first positive lens Lp1 and the second positive lens Lp2 are both lenses whose lens surfaces are formed as spherical. By forming the lens surfaces of the positive lens Lp1 and the positive lens Lp2 as spherical, it is possible to reduce performance degradation due to decentering. It is also possible to avoid performance degradation due to aspherical shape errors, which have a significant effect on lenses with high refractive indexes.

[0069] Next, a description will be given of an eyepiece optical system according to the second embodiment. As shown in FIG. 1, an eyepiece optical system EL (EL1) as an example of the eyepiece optical system EL according to the second embodiment has at least five lenses.

[0070] With the above-described configuration, the eyepiece optical system EL according to the second embodiment satisfies the following conditional expression (11): 0.400<h / fe<0.500 (11) where fe is the combined focal length of the eyepiece optical system EL, and h is the maximum object height of the object Ob to be observed through the eyepiece optical system EL.

[0071] According to the second embodiment, it is possible to obtain an eyepiece optical system having good optical performance in which various aberrations, particularly astigmatism and distortion, are corrected, and an optical apparatus equipped with this eyepiece optical system. The variable magnification optical system ZL according to the second embodiment may be the eyepiece optical system EL (EL2) shown in Fig. 3, the eyepiece optical system EL (EL3) shown in Fig. 5, the eyepiece optical system EL (EL4) shown in Fig. 7, the eyepiece optical system EL (EL5) shown in Fig. 9, the eyepiece optical system EL (EL6) shown in Fig. 11, or the eyepiece optical system EL (EL7) shown in Fig. 13.

[0072] By configuring the eyepiece optical system EL to have at least five lenses, various aberrations can be corrected well. If the number of lenses were four or less, the refractive power of each lens would be too strong, making aberration correction difficult.

[0073] Conditional expression (11) is the same as that of the first embodiment, and the same effect can be obtained. If the corresponding value of conditional expression (11) exceeds the upper limit, the field of view becomes too large, making it difficult to correct off-axis aberrations, which is undesirable. By setting the upper limit of conditional expression (11) to 0.480, 0.470, 0.460, or even 0.450, the effect of this embodiment can be made more certain.

[0074] If the corresponding value of conditional expression (11) falls below the lower limit, the magnification of the eyepiece optical system EL becomes high, making it difficult to correct various aberrations. By setting the lower limit of conditional expression (11) to 0.420, 0.430, or even 0.440, the effect of this embodiment can be made even more certain.

[0075] In the eyepiece optical system EL according to the second embodiment, it is preferable to satisfy the following conditional expression (11): 0.400<h / fe<0.500 (11) where fe is the combined focal length of the eyepiece optical system EL, and h is the maximum object height of the object Ob to be observed in the eyepiece optical system EL.

[0076] Conditional expression (11) is the same as that of the first embodiment, and the same effect can be obtained. If the corresponding value of conditional expression (11) exceeds the upper limit, the field of view becomes too large, making it difficult to correct off-axis aberrations, which is undesirable. By setting the upper limit of conditional expression (11) to 0.480, 0.470, 0.460, or even 0.450, the effect of this embodiment can be made more certain.

[0077] If the corresponding value of conditional expression (11) falls below the lower limit, the magnification of the eyepiece optical system EL becomes high, making it difficult to correct various aberrations. By setting the lower limit of conditional expression (11) to 0.420, 0.430, or even 0.440, the effect of this embodiment can be made even more certain.

[0078] The eyepiece optical system EL according to the second embodiment preferably has at least one lens having an aspherical surface formed on a lens surface that satisfies the following condition (12): 0.000≦D aspe / ΣD<0.200 (12) where D aspe is the distance on the optical axis from the aspherical surface closest to the eyepoint to the lens surface of the eyepiece optical system EL closest to the eyepoint, and ΣD is the distance on the optical axis from the lens surface closest to the object to be observed Ob to the lens surface closest to the eyepoint EP.

[0079] Conditional expression (12) is the same as that in the first embodiment, and the same effect can be obtained. By satisfying conditional expression (12), spherical aberration and coma that occur on the eyepoint EP side can be effectively corrected by the aspherical surface.

[0080] If the corresponding value of conditional expression (12) exceeds the upper limit, the position of the aspherical surface located closest to the eyepoint EP will be farther away from the eyepoint EP, making it difficult to correct spherical aberration and coma that occur on the eyepoint EP side. By setting the upper limit of conditional expression (12) to 0.190 or even 0.170, the effect of this embodiment can be further ensured. The lower limit of conditional expression (12) represents the lens surface closest to the eyepoint EP.

[0081] The eyepiece optical system EL according to the second embodiment preferably has at least one lens having an aspherical surface formed on a lens surface that satisfies the following conditional expression (13): 0.000≦Daspo / ΣD<0.200 (13) where Daspo is the distance on the optical axis from the lens surface of the eyepiece optical system EL closest to the object to be observed Ob to the aspherical surface closest to the object to be observed Ob of the aspherical surfaces, and ΣD is the distance on the optical axis from the lens surface closest to the object to be observed Ob to the lens surface closest to the eyepoint EP.

[0082] Conditional expression (13) is the same as that in the first embodiment, and the same effect can be obtained. By satisfying conditional expression (13), distortion occurring on the side of the eyepiece optical system EL facing the object under observation Ob can be effectively corrected by the aspheric surface.

[0083] If the corresponding value of conditional expression (13) exceeds the upper limit, the position of the aspherical surface arranged closest to the observed object Ob will be farther away from the observed object Ob, making it difficult to correct distortion occurring on the observed object Ob side. By setting the upper limit of conditional expression (13) to 0.190 or even 0.170, the effect of this embodiment can be further ensured. The lower limit of conditional expression (13) represents the lens surface closest to the observed object Ob.

[0084] The eyepiece optical system EL according to the second embodiment preferably has at least one lens La having an aspherical lens surface with an inflection point on the aspherical surface where the radius of curvature reverses from positive to negative or from negative to positive, and satisfies the following conditional expression (14): 0.20<y / Ry<0.85 (14), where y is the distance between the optical axis of the lens La and the inflection point in a direction perpendicular to the optical axis, and Ry is the radius of the lens La.

[0085] Conditional expression (14) is the same as that of the first embodiment, and the same effect can be obtained. By satisfying conditional expression (14), an inflection point is provided at the periphery of the optical axis within the aperture of lens La, and distortion can be effectively corrected by the inflection point. The inflection point is the position at which the radius of curvature inverts, and the radius of curvature inverts from positive to negative, or from negative to positive, at this position. It is desirable that the lens having the aspherical surface closest to the object under observation Ob, among the aspherical surfaces, be configured as lens La having an inflection point. Such a configuration can effectively correct distortion. Furthermore, by configuring lens La as a lens having positive refractive power paraxially and having an inflection point at the periphery, telecentricity on the side of the object under observation Ob can be improved.

[0086] If the corresponding value of conditional expression (14) exceeds the upper limit, distortion at intermediate image heights will undesirably worsen. By setting the upper limit of conditional expression (14) to 0.700, or even 0.500, the effect of this embodiment can be made even more certain.

[0087] If the corresponding value of conditional expression (14) falls below the lower limit, the curvature of field will undesirably worsen. By setting the lower limit of conditional expression (14) to 0.250 or even 0.300, the effect of this embodiment can be made more certain.

[0088] The eyepiece optical system EL according to the second embodiment is preferably constructed with at least five lenses. This configuration allows for good correction of various aberrations. If the number of lenses were four or less, the refractive power of each lens would be too strong, making aberration correction difficult.

[0089] Next, an eyepiece optical system according to a third embodiment will be described. As shown in Figures 1 and 15, the eyepiece optical system EL (EL1) is an example of the eyepiece optical system EL according to the third embodiment, and is an eyepiece optical system for observing an image displayed on an image display element, and includes at least five lenses.

[0090] According to the third embodiment, it is possible to obtain an eyepiece optical system having good optical performance in which various aberrations, particularly astigmatism and distortion, are corrected, and an optical apparatus equipped with this eyepiece optical system. The variable magnification optical system ZL according to the second embodiment may be the eyepiece optical system EL (EL2) shown in Fig. 3, the eyepiece optical system EL (EL3) shown in Fig. 5, the eyepiece optical system EL (EL4) shown in Fig. 7, the eyepiece optical system EL (EL5) shown in Fig. 9, the eyepiece optical system EL (EL6) shown in Fig. 11, or the eyepiece optical system EL (EL7) shown in Fig. 13.

[0091] By configuring the eyepiece optical system EL to have at least five lenses, various aberrations can be corrected well. If the number of lenses were four or less, the refractive power of each lens would be too strong, making aberration correction difficult.

[0092] In the eyepiece optical system EL according to the third embodiment, it is preferable to satisfy the following conditional expression (11): 0.400<h / fe<0.500 (11) where fe is the combined focal length of the eyepiece optical system EL, and h is the maximum object height of the object Ob to be observed in the eyepiece optical system EL.

[0093] Conditional expression (11) is the same as that in the first and second embodiments, and the same effect can be obtained. By satisfying conditional expression (11), various aberrations can be corrected well even if the field of view is large.

[0094] If the corresponding value of conditional expression (11) exceeds the upper limit, the field of view becomes too large, making it difficult to correct off-axis aberrations, which is undesirable. By setting the upper limit of conditional expression (11) to 0.480, 0.470, 0.460, or even 0.450, the effect of this embodiment can be made more certain.

[0095] If the corresponding value of conditional expression (11) falls below the lower limit, the magnification of the eyepiece optical system EL becomes high, making it difficult to correct various aberrations. By setting the lower limit of conditional expression (11) to 0.420, 0.430, or even 0.440, the effect of this embodiment can be made even more certain.

[0096] The eyepiece optical system EL according to the third embodiment preferably has at least one lens having an aspherical surface formed on a lens surface that satisfies the following condition (12): 0.000≦D aspe / ΣD<0.200 (12) where D aspe is the distance on the optical axis from the aspherical surface closest to the eyepoint to the lens surface of the eyepiece optical system EL closest to the eyepoint, and ΣD is the distance on the optical axis from the lens surface closest to the object to be observed Ob to the lens surface closest to the eyepoint EP.

[0097] Conditional expression (12) is the same as that in the first and second embodiments, and the same effect can be obtained. By satisfying conditional expression (12), spherical aberration and coma that occur on the eyepoint EP side can be effectively corrected by the aspherical surface.

[0098] If the corresponding value of conditional expression (12) exceeds the upper limit, the position of the aspherical surface located closest to the eyepoint EP will be farther away from the eyepoint EP, making it difficult to correct spherical aberration and coma that occur on the eyepoint EP side. By setting the upper limit of conditional expression (12) to 0.190 or even 0.170, the effect of this embodiment can be further ensured. The lower limit of conditional expression (12) represents the lens surface closest to the eyepoint EP.

[0099] The eyepiece optical system EL according to the third embodiment preferably has at least one lens having an aspherical surface formed on a lens surface that satisfies the following conditional expression (13): 0.000≦Daspo / ΣD<0.200 (13) where Daspo is the distance on the optical axis from the lens surface of the eyepiece optical system EL closest to the object to be observed Ob to the aspherical surface closest to the object to be observed Ob of the aspherical surfaces, and ΣD is the distance on the optical axis from the lens surface closest to the object to be observed Ob to the lens surface closest to the eyepoint EP.

[0100] Conditional expression (13) is the same as that in the first and second embodiments, and the same effect can be obtained. By satisfying conditional expression (13), distortion occurring on the side of the eyepiece optical system EL facing the object to be observed Ob can be effectively corrected by the aspheric surface.

[0101] If the corresponding value of conditional expression (13) exceeds the upper limit, the position of the aspherical surface arranged closest to the observed object Ob will be farther away from the observed object Ob, making it difficult to correct distortion occurring on the observed object Ob side. By setting the upper limit of conditional expression (13) to 0.190 or even 0.170, the effect of this embodiment can be further ensured. The lower limit of conditional expression (13) represents the lens surface closest to the observed object Ob.

[0102] The eyepiece optical system EL according to the third embodiment preferably has at least one lens La having an aspherical lens surface with an inflection point on the aspherical surface where the radius of curvature reverses from positive to negative or from negative to positive, and satisfies the following conditional expression (14): 0.20<y / Ry<0.85 (14), where y is the distance between the optical axis of the lens La and the inflection point in a direction perpendicular to the optical axis, and Ry is the radius of the lens La.

[0103] Conditional expression (14) is the same as that in the first and second embodiments, and the same effect can be obtained. By satisfying conditional expression (14), an inflection point is provided at the periphery of the optical axis within the aperture of lens La, and distortion can be effectively corrected by the inflection point. The inflection point is the position at which the radius of curvature inverts, and the radius of curvature inverts from positive to negative or from negative to positive across this position. It is desirable that the lens having the aspherical surface closest to the object under observation Ob be configured as lens La with an inflection point. Such a configuration can effectively correct distortion. Furthermore, by configuring lens La as a lens with positive refractive power paraxially and with an inflection point at the periphery, telecentricity on the side of the object under observation Ob can be improved.

[0104] If the corresponding value of conditional expression (14) exceeds the upper limit, distortion at intermediate image heights will undesirably worsen. By setting the upper limit of conditional expression (14) to 0.700, or even 0.500, the effect of this embodiment can be made even more certain.

[0105] If the corresponding value of conditional expression (14) falls below the lower limit, the curvature of field will undesirably worsen. By setting the lower limit of conditional expression (14) to 0.250 or even 0.300, the effect of this embodiment can be made more certain.

[0106] In the eyepiece optical systems EL according to the first to third embodiments described above, it is preferable to satisfy the following conditional expression (15): 20.000 mm<De<30.000 mm (15), where De is the distance on the optical axis from the lens surface of the eyepiece optical system EL closest to the eyepoint EP to the eyepoint EP.

[0107] Condition (15) defines the distance on the optical axis from the lens surface of the eyepiece optical system EL closest to the eyepoint EP to the eyepoint EP. By satisfying condition (15), various aberrations such as distortion, spherical aberration, and coma can be effectively corrected.

[0108] If the value corresponding to conditional expression (15) exceeds the upper limit, a convex lens with strong positive refractive power will be located at a position away from the aperture stop located outside the eyepiece optical system EL, which is undesirable because it makes correction of distortion difficult. By setting the upper limit of conditional expression (15) to 28,000 or even 26,000, the effect of this embodiment can be made even more certain.

[0109] If the corresponding value of conditional expression (15) falls below the lower limit, the separation between the on-axis light beam and the off-axis light beam on the eyepoint EP side becomes small, making it difficult to correct spherical aberration and coma, which is undesirable. By setting the lower limit of conditional expression (15) to 21,000 or even 22,000, the effect of this embodiment can be made even more certain.

[0110] In the eyepiece optical systems EL according to the first to third embodiments described above, it is preferable to satisfy the following conditional expression (16): 1.100<De / fe<1.500 (16) where De is the distance on the optical axis from the lens surface of the eyepiece optical system EL closest to the eyepoint EP to the eyepoint EP, and fe is the combined focal length of the eyepiece optical system EL.

[0111] Condition (16) defines an appropriate range for the ratio of the axial distance from the lens surface of the eyepiece optical system EL closest to the eyepoint EP to the eyepoint EP to the overall focal length of the eyepiece optical system EL. By satisfying condition (16), various aberrations such as distortion, spherical aberration, and coma can be effectively corrected.

[0112] If the value corresponding to conditional expression (16) exceeds the upper limit, the aperture stop will be located outside the eyepiece optical system EL, and a convex lens with strong positive refractive power will be located at a position away from the aperture stop, which is undesirable because it will make correction of distortion difficult. By setting the upper limit of conditional expression (16) to 1.450, 1.400, or even 1.350, the effect of this embodiment can be made even more certain.

[0113] If the corresponding value of conditional expression (16) falls below the lower limit, the separation between the on-axis light beam and the off-axis light beam on the eyepoint EP side becomes small, making it difficult to correct spherical aberration and coma, which is undesirable. By setting the lower limit of conditional expression (16) to 1.200, 1.240, 1.280, or even 1.300, the effect of this embodiment can be made more certain.

[0114] In the eyepiece optical systems EL according to the first to third embodiments described above, it is preferable that the lens positioned closest to the object under observation Ob has positive refractive power. This configuration allows for good correction of distortion. Furthermore, placing a lens with negative refractive power closest to the object under observation Ob is undesirable because it increases the size of the lens in the radial direction.

[0115] In the eyepiece optical systems EL according to the first to third embodiments described above, it is preferable to satisfy the following conditional expression (17): 0.250<D0 / fe<0.500 (17) where D0 is the diopter when the diopter is 0 [m －１ fe: the combined focal length of the eyepiece optical system EL.

[0116] Condition (17) satisfies the condition that the diopter is 0 [m －１ ], to the overall focal length of the eyepiece optical system EL. By satisfying conditional expression (17), it is possible to satisfactorily correct various aberrations such as curvature of field and distortion, and to maintain telecentricity on the side of the observed object Ob.

[0117] If the value corresponding to conditional expression (17) exceeds the upper limit, the lens surface closest to the observed object Ob becomes farther away from the observed object Ob, making it difficult to correct curvature of field and distortion. By setting the upper limit of conditional expression (17) to 0.480, 0.460, 0.440, or even 0.420, the effect of this embodiment can be further ensured.

[0118] If the value corresponding to conditional expression (17) falls below the lower limit, the lens surface closest to the observed object Ob will be too close to the observed object Ob, which is undesirable because it will destroy the telecentricity on the side of the observed object Ob. By setting the lower limit of conditional expression (17) to 0.300, 0.350, or even 0.400, the effect of this embodiment can be made more certain.

[0119] In the eyepiece optical systems EL according to the first to third embodiments described above, it is preferable to satisfy the following conditional expression (18): 0.120<D0 / TL<0.250 (18) where D0 is the diopter when the diopter is 0 [m －１ ], TL: the distance on the optical axis from the object to be observed Ob to the lens surface closest to the object to be observed Ob when the diopter is 0 [m －１ ] on the optical axis from the object to be observed Ob to the lens surface closest to the eyepoint EP

[0120] Condition (18) satisfies the condition that the diopter is 0 [m －１ ], and the distance on the optical axis from the object to be observed Ob to the lens surface closest to the object to be observed Ob, and the diopter is 0 [m －１

[0063] The condition (18) defines within an appropriate range the ratio of the on-optical-axis distance from the object under observation Ob to the lens surface closest to the eyepoint EP. By satisfying condition (18), various aberrations such as curvature of field and distortion can be effectively corrected, and telecentricity on the side of the object under observation Ob can be ensured.

[0121] If the value corresponding to conditional expression (18) exceeds the upper limit, the lens surface closest to the observed object Ob becomes farther away from the observed object Ob, making it difficult to correct curvature of field and distortion. By setting the upper limit of conditional expression (18) to 0.240 or even 0.230, the effect of this embodiment can be made even more certain.

[0122] If the corresponding value of conditional expression (18) falls below the lower limit, the lens surface closest to the observed object Ob will be too close to the observed object Ob, making it difficult to ensure telecentricity on the side of the observed object Ob, which is undesirable. By setting the lower limit of conditional expression (18) to 0.125, 0.150, or even 0.200, the effect of this embodiment can be made more certain.

[0123] In the eyepiece optical systems EL according to the first to third embodiments described above, it is preferable to satisfy the following conditional expression (19): 0.080<ΣDair / ΣD<0.200 (19) where ΣDair is the sum of the air spaces between the lenses from the lens closest to the object under observation Ob to the lens closest to the eyepoint EP, and ΣD is the distance on the optical axis from the lens surface closest to the object under observation Ob to the lens surface closest to the eyepoint EP.

[0124] Conditional expression (19) defines within an appropriate range the ratio of the sum of the air gaps between the lenses from the lens closest to the object under observation Ob to the lens closest to the eyepoint EP to the distance on the optical axis from the lens surface closest to the object under observation Ob to the lens surface closest to the eyepoint EP. By satisfying conditional expression (19), various aberrations can be effectively corrected. Note that optical elements without refractive power, such as prisms, may be used before and after the eyepiece optical system EL. When an optical element without refractive power, such as a prism, is used in the eyepiece optical system EL, ΣDair is preferably the air-equivalent length from the lens closest to the object under observation Ob to the lens closest to the eyepoint EP. In other words, ΣDair is the air-equivalent length including optical elements without refractive power, such as prisms.

[0125] If the value corresponding to conditional expression (19) exceeds the upper limit, the distance between the lenses becomes large, making it difficult to correct various aberrations. By setting the upper limit of conditional expression (19) to 0.180, 0.170, 0.160, or even 0.150, the effect of this embodiment can be made more certain.

[0126] If the corresponding value of conditional expression (19) is below the lower limit, it is necessary to reduce the difference in the radii of curvature between the convex and concave surfaces of adjacent lenses, making it difficult to correct aberrations between the convex and concave surfaces. By setting the lower limit of conditional expression (19) to 0.085, 0.090, 0.100, or even 0.110, the effects of this embodiment can be made more certain.

[0127] In the eyepiece optical systems EL according to the first to third embodiments described above, it is preferable that the lens positioned closest to the object under observation Ob has positive refractive power, and that the lens positioned adjacent to the lens closest to the object under observation Ob on the eyepoint side also has positive refractive power. This configuration makes it easy to correct both distortion and spherical aberration.

[0128] In the eyepiece optical systems EL according to the first to third embodiments described above, the number of lenses having positive refractive power is preferably four. With this configuration, the convex refractive power of each lens can be weakened, resulting in good correction of various aberrations.

[0129] In the eyepiece optical systems EL according to the first to third embodiments described above, it is preferable to satisfy the following conditional expression (20): 1.00<f1 / fe<2.50 (20), where f1 is the focal length of the lens arranged closest to the object to be observed, and fe is the combined focal length of the eyepiece optical system.

[0130] Condition (20) defines an appropriate range for the ratio of the focal length of the lens closest to the object to the overall focal length of the eyepiece optical system EL. By satisfying condition (20), various aberrations can be effectively corrected.

[0131] If the value corresponding to conditional expression (20) exceeds the upper limit, the positive refractive power of the lens closest to the object to be observed will be weakened, causing distortion to worsen and making correction of aberrations difficult. By setting the upper limit of conditional expression (20) to 2.00, 2.10, or even 2.30, the effects of this embodiment can be made even more certain.

[0132] If the value corresponding to conditional expression (20) falls below the lower limit, the positive refractive power of the lens closest to the object to be observed becomes strong, which worsens the curvature of field and makes it difficult to correct aberrations. By setting the lower limit of conditional expression (20) to 1.10, 1.20, or even 1.25, the effect of this embodiment can be made even more certain.

[0133] In the eyepiece optical systems EL according to the first to third embodiments described above, it is preferable to satisfy the following conditional expression (21): 1.50<fep / fe<5.00 (21) where fep is the focal length of the lens located closest to the eyepoint, and fe is the combined focal length of the eyepiece optical system.

[0134] Condition (21) defines an appropriate range for the ratio of the focal length of the lens closest to the eyepoint to the overall focal length of the eyepiece optical system EL. By satisfying condition (21), various aberrations can be effectively corrected.

[0135] If the value corresponding to conditional expression (21) exceeds the upper limit, the positive refractive power of the lens closest to the eyepoint becomes weak, making it difficult to increase the observation magnification while maintaining good curvature of field. By setting the upper limit of conditional expression (21) to 4.10, 4.20, or even 4.30, the effect of this embodiment can be made more certain.

[0136] If the corresponding value of conditional expression (21) falls below the lower limit, the positive refractive power of the lens closest to the eyepoint becomes strong, causing spherical aberration and coma to worsen, making it difficult to correct aberrations. By setting the lower limit of conditional expression (21) to 1.60, 1.65, or even 1.70, the effect of this embodiment can be made more certain.

[0137] According to the present embodiment described above, it is possible to obtain an eyepiece optical system having good optical performance in which various aberrations, particularly astigmatism and distortion, are corrected, and an optical apparatus equipped with this eyepiece optical system.

[0138] The observation optical systems EL according to Examples of this embodiment will be described below with reference to the drawings. FIGS. 1, 3, 5, 7, 9, 11, and 13 are cross-sectional views showing the configuration and refractive power distribution of the observation optical systems EL {EL(1) to EL(7)} according to Examples 1 to 7. In these figures ( FIGS. 1, 3, 5, 7, 9, and 13), each lens is represented by a combination of the symbol L and a number. To avoid complication due to the large number and variety of symbols and numbers, each Example uses its own unique combination of symbols and numbers to represent the lens groups, etc. Therefore, even if the same combination of symbols and numbers is used between Examples, this does not necessarily mean that the structures are identical. Furthermore, the symbol (+) or (-) attached to each lens group symbol indicates the refractive power of that lens group, and this is the same for all Examples below.

[0139] Tables 1 to 7 are shown below, with Table 1 showing data on the various specifications for Example 1, Table 2 for Example 2, Table 3 for Example 3, Table 4 for Example 4, Table 5 for Example 5, Table 6 for Example 6, and Table 7 for Example 7. In each example, the d-line (wavelength λ=587.6 nm) and g-line (wavelength λ=435.8 nm) were selected as the targets for calculating aberration characteristics.

[0140] In the table, in the [Overall Specifications], fe is the focal length of the entire eyepiece optical system EL, TL is the total length of the eyepiece optical system EL (visor 0 [m -1]), ΣD is the distance on the optical axis from the lens surface closest to the object under observation Ob to the lens surface closest to the eyepoint EP, ΣDair is the total air space between the lens closest to the object under observation Ob to the lens closest to the eyepoint EP, Daspe is the distance on the optical axis from the lens surface closest to the object under observation Ob in the eyepiece optical system EL to the aspherical surface closest to the object under observation Ob, Daspo is the distance on the optical axis from the lens surface closest to the object under observation Ob in the eyepiece optical system EL to the aspherical surface closest to the object under observation Ob where Np1 is the distance on the optical axis to the aspherical surface on the body side Ob, Np2 is the refractive index of the first positive lens Lp1 for the d-line, Np1 is the refractive index of the second positive lens Lp2 for the d-line, Nn1 is the refractive index of the first negative lens Ln1 for the d-line, Nn2 is the refractive index of the second negative lens Ln2 for the d-line, fLp1 is the focal length of the first positive lens Lp1, fLp2 is the focal length of the second positive lens Lp2, νp1 is the Abbe number of the first positive lens Lp1 based on the d-line, νp2 is the Abbe number of the second positive lens Lp2 based on the d-line, and νn1 is the Abbe number of the first negative lens Ln1 based on the d-line.

[0141] In the [Lens Specifications] table, the surface number indicates the order of the optical surface from the side of the object under observation Ob along the direction of light travel, r indicates the radius of curvature of each optical surface, D indicates the surface spacing, which is the distance on the optical axis from each optical surface to the next optical surface (or eye point EP), νd indicates the Abbe number based on the d-line of the lens material, nd indicates the refractive index of the lens material with respect to the d-line, "∞" in the column for radius of curvature r indicates a flat surface, and EP indicates the eye point. The refractive index of air, "1.0000," is omitted. If the optical surface is aspherical, an * is added to the surface number, and the column for radius of curvature r indicates the paraxial radius of curvature.

[0142] In the table, "Aspherical Data" indicates the shape of the aspherical surface shown in "Lens Specifications" using the following formula (a): X(y) is the distance along the optical axis from the tangent plane at the vertex of the aspherical surface to the position on the aspherical surface at height y, r is the radius of curvature of the reference spherical surface (paraxial radius of curvature), κ is the conic constant, and Ai is the ith aspherical coefficient. "E-n" is "×10 -n For example, 1.234E-05 = 1.234 x 10 -5 is.

[0143] X(y)=(y 2 / r) / {1+(1-κ・y 2 / r 2 ) 1 / 2} + A4 × y 4 +A6×y 6 +A8×y 8 ...(a)

[0144] [Variable Distance Data] shows the changes in D0 and De shown in [Lens Specifications] that change with diopter adjustment. D0 is the diopter 0 [m －１ ], De is the distance on the optical axis from the lens surface of the eyepiece optical system EL closest to the eyepoint EP to the eyepoint EP, TL is the total length of the eyepiece optical system EL (diopter 0 [m －１ ]) on the optical axis from the surface of the object to be observed Ob to the lens surface closest to the eye point EP. The unit of diopter is "m －１ " is used. Diopter x "m －１ " indicates that the image formed by the eyepiece optical system EL is formed at a position 1 / X [m (meters)] on the optical axis from the eyepoint EP (however, the sign is positive when the image is formed on the observer side of the eyepiece optical system EL).

[0145] In the following, all specifications such as focal length f, radius of curvature r, surface spacing D, and other lengths are generally expressed in "mm" unless otherwise specified, but this is not limited to this because the same optical performance can be obtained with proportional enlargement or reduction of an optical system. Furthermore, the unit is not limited to "mm" and other appropriate units can be used.

[0146] The explanation of the tables up to this point is common to all the embodiments, and will not be repeated below.

[0147] First Example The first example will be described with reference to Fig. 1, Fig. 2 and Table 1. The eyepiece optical system EL (EL1) according to the first example, as shown in Fig. 1, is composed of, arranged in order from the side of the observed object (image display element) Ob along the optical axis, a first lens L1 having positive refractive power, a second lens L2 having positive refractive power, a third lens L3 having negative refractive power, a fourth lens having negative refractive power, a fifth lens having positive refractive power, and a sixth lens having positive refractive power.

[0148] The first lens L1 is a biconvex positive lens. The lens surfaces of the first lens facing the object to be observed Ob and the eyepoint EP are aspheric. The aspheric surfaces have inflection points at which the curvature changes from positive to negative or from negative to positive in the peripheral area within the aperture.

[0149] The second lens L2 is a positive meniscus lens with a concave surface facing the observed object Ob.

[0150] The third lens L3 is a negative meniscus lens with a concave surface facing the object to be observed Ob, and the lens surface of the third lens L3 facing the object to be observed Ob is aspheric.

[0151] The fourth lens L4 is a negative biconcave lens, and the lens surface of the fourth lens L4 facing the object to be observed Ob is aspheric.

[0152] The fifth lens L5 is a positive lens having a biconvex surface shape.

[0153] The sixth lens L6 is a positive meniscus lens with a convex surface facing the object to be observed Ob. Aspheric surfaces are formed on both lens surfaces of the sixth lens L6.

[0154] Diopter adjustment is performed by moving the first lens L1 to the sixth lens L6 together along the optical axis.

[0155] In this example, the fifth lens L5 constitutes the first positive lens Lp1, and the second lens L2 constitutes the second positive lens Lp2. The third lens L3 constitutes the first negative lens Ln1, and the fourth lens L4 constitutes the second negative lens Ln2. The first lens L1 constitutes a lens La having an inflection point on its aspheric surface. The lens arranged closest to the object to be observed is the first lens L1, and the lens arranged closest to the eyepoint is the sixth lens L6.

[0156] Table 1 below shows the values ​​of each parameter in Example 1. The surface numbers in Table 1 correspond to the optical surfaces in Figure 1. In Example 1, surfaces 1, 2, 5, 7, 11, and 12 are formed aspherically.

[0157] 1, each reference symbol is used independently for each embodiment to avoid complication of explanation due to an increase in the number of digits of the reference symbol. Therefore, even if a reference symbol common to drawings relating to other embodiments is used, that does not necessarily mean that the configuration is common to those other embodiments.

[0158] (Table 1) [Overall Specifications] fe = 18.206 TL = 32.965 ΣD = 25.542 ΣDair = 2.734 Daspe = 0.000 Daspo = 0.000 Np1 = 1.883 Np2 = 1.883 Nn1 = 1.636 Nn2 = 1.636 fLp1 = 17.416 fLp2 = 21.203 νp1 = 40.69 νp2 = 40.69 νn1 = 23.89 [Lens Specifications] Surface No. r D νd nd ∞ D0 *1 30.7477 3.155 55.71 1.535037 *2 -24.1080 0.160 3 -107.4267 6.441 40.69 1.883000 4 -16.3916 2.097 *5 -9.1203 1.500 23.89 1.635500 6 -56.4844 0.236 *7 -40.4146 1.500 23.89 1.635500 8 30.6024 0.140 9 31.9528 8.245 40.69 1.883000 10 -26.0603 0.100 *11 31.5758 1.967 55.71 1.535037 *12 469.9409 De EP [Aspherical Data] First Surface κ = 1.0000, A4 = -1.78550E-04, A6 = 5.97416E-07, A8 = -6.09944E-09 Second Surface κ = 1.0000, A4 = 1.4758992E-06,A6=2.97567E-08,A8=0.00000E+00 11th page κ=1.0000,A4=-3.37528E-05,A6=2.22950E-07,A8=-4.76586E-10 12th page κ=1.0000,A4=5.89071E-05,A6=6.30686E-08,A8=0.00000E+00 [Variable interval data] Diopter -1 [m. -1 ] 0[m -1 ] -4[m -1 ] +2[m -1 ] D0 7.0862 7.4231 6.0049 8.0651 De 24.0000 23.7810 24.8220 23.4050 [Lens group data] f1 25.773 f2 21.203 f3 -17.328 f4 -27.181 f5 17.416 f6 63.168

[0159] From the specifications shown in Table 1, it can be seen that the eyepiece optical system EL1 according to the first example satisfies conditional expressions (1) to (21).

[0160] FIG. 2 shows the diopter of the eyepiece optical system EL1 according to the first example, −1 [m -1 ] shows various aberration diagrams (spherical aberration, astigmatism, coma, distortion, and lateral chromatic aberration) at this time.

[0161] In each aberration diagram, the vertical axis of the spherical aberration diagram indicates the height of incidence of light emitted from the center of the optical axis of the object under observation Ob onto the tangent plane of the lens surface of the first lens L1 of the eyepiece optical system EL1 facing the object under observation Ob, and the vertical axis YO of the astigmatism diagram and distortion diagram indicates the size (radius) of the object under observation Ob. d indicates the aberration curve for the d-line, and g indicates the aberration curve for the g-line. Furthermore, values ​​without a notation indicate aberration curves for the d-line. In the astigmatism diagram, the solid line indicates the sagittal image plane, and the dashed line indicates the meridional image plane. Furthermore, in the aberration diagram showing coma aberration, meridional coma is indicated. In the spherical aberration diagram and the astigmatism diagram, the horizontal axis is in units of [m -1 ] and is indicated by "D." in the figure.

[0162] The above explanation regarding the aberration diagrams is similar to that for the other examples, and the explanation thereof will be omitted.

[0163] As is clear from the various aberration diagrams shown in FIG. 2, the eyepiece optical system EL1 according to the first example effectively corrects various aberrations, particularly astigmatism and distortion, ensuring excellent optical performance.

[0164] Second Example The second example will be described with reference to Fig. 3, Fig. 4 and Table 2. As shown in Fig. 3, the eyepiece optical system EL (EL2) according to the second example comprises, arranged along the optical axis in order from the side of the observed object (image display element) Ob, a first lens L1 having positive refractive power, a second lens L2 having positive refractive power, a third lens L3 having negative refractive power, a fourth lens having positive refractive power, a fifth lens having negative refractive power, and a sixth lens having positive refractive power.

[0165] The first lens L1 is a biconvex positive lens. Both lens surfaces of the first lens L1 are aspherical. The aspherical surfaces have inflection points at which the curvature changes from positive to negative or from negative to positive in the peripheral portion within the aperture.

[0166] The second lens L2 is a positive meniscus lens with a concave surface facing the observed object Ob.

[0167] The third lens L3 is a negative meniscus lens with a concave surface facing the object to be observed Ob, and the lens surface of the third lens L3 facing the object to be observed Ob is aspheric.

[0168] The fourth lens L4 is a positive meniscus lens with a concave surface facing the observed object Ob.

[0169] The fifth lens L5 is a negative meniscus lens with a convex surface facing the object to be observed Ob, and both lens surfaces of the fifth lens L5 are aspheric.

[0170] The sixth lens L6 is a positive meniscus lens with a convex surface facing the observed object Ob.

[0171] Diopter adjustment is performed by moving the first lens L1 to the sixth lens L6 together along the optical axis.

[0172] In this example, the second lens L2 constitutes the first positive lens Lp1, and the fourth lens L4 constitutes the second positive lens Lp2. The third lens L3 constitutes the first negative lens Ln1, and the fifth lens L5 constitutes the second negative lens Ln2. The first lens L1 constitutes a lens La having an inflection point on its aspheric surface. The lens closest to the object to be observed is the first lens L1, and the lens closest to the eyepoint is the sixth lens L6.

[0173] Table 2 below shows the values ​​of each parameter in Example 2. The surface numbers in Table 2 correspond to the optical surfaces in Figure 3. In Example 2, surfaces 1, 2, 5, 9, and 10 are formed aspherically.

[0174] (Table 2) [Overall Specifications] fe = 18.148 TL = 35.861 ΣD = 29.587 ΣDair = 4.744 Daspe = 4.681 Daspo = 0.000 Np1 = 1.816 Np2 = 1.816 Nn1 = 1.636 Nn2 = 1.636 fLp1 = 20.474 fLp2 = 27.613 νp1 = 46.59 νp2 = 46.59 νn1 = 23.89 [Lens Specifications] Surface Number r D νd nd ∞ D0 *1 26.5711 1.206 55.71 1.535037 *2 -62.7078 0.100 3 -107.6728 7.800 46.59 1.816000 4 -14.9332 3.970 *5 -9.1205 1.756 23.89 1.635500 6 -91.0615 0.100 7 -104.3286 8.692 46.59 1.816000 8 -19.2237 0.100 *9 26.0438 1.183 23.89 1.635500 *10 16.6161 0.473 11 17.5952 4.207 47.35 1.788000 12 56.4147 De EP [Aspherical Data] First Surface κ = 1.0000, A4 = -2.42203E-04, A6 = -8.43861E-08, A8 = -1.44518E-09 Second Surface κ = 1.0000, A4 = 3.45500E-05, A6 = -5.75821E-08, A8 = 0.00000E+00 Fifth Surface κ = 0.5205, A4 = 2.24960E-04, A6 = -5.18571E-07, A8 = 1.83367E-09 Ninth Surface κ = 1.0000, A4 = -6.26763E-05,A6=2.15008E-07,A8=0.00000E+00 10th surface κ=1.0000,A4=5.85286E-06,A6=9.69503E-08,A8=0.00000E+00 [Variable interval data] Diopter -1 [m. -1 ] 0[m -1 ] -4[m -1 ] +2[m -1 ] D0 5.9387 6.2746 4.8462 6.9086 De 24.0000 23.6970 25.1110 23.1660 [Lens group data] f1 35.047 f2 20.474 f3 -16.083 f4 27.613 f5 -75.932 f6 30.970

[0175] From the specifications shown in Table 2, it can be seen that the eyepiece optical system EL2 according to the second example satisfies conditional expressions (1) to (21).

[0176] FIG. 4 shows the diopter of the eyepiece optical system EL2 according to the second example, −1 [m -1 ] shows various aberration diagrams (spherical aberration, astigmatism, coma, distortion, and lateral chromatic aberration) at this time.

[0177] As is clear from the various aberration diagrams shown in FIG. 4, the eyepiece optical system EL2 according to the second example has various aberrations, particularly astigmatism and distortion, corrected well, ensuring excellent optical performance.

[0178] Third Example The third example will be described with reference to Fig. 5, Fig. 6 and Table 3. As shown in Fig. 5, the eyepiece optical system EL (EL3) according to the third example comprises, arranged in order from the side of the observed object (image display element) Ob along the optical axis, a first lens L1 having positive refractive power, a second lens L2 having positive refractive power, a third lens L3 having negative refractive power, a fourth lens having negative refractive power, a fifth lens having positive refractive power, and a sixth lens having positive refractive power.

[0179] The first lens L1 is a biconvex positive lens. The lens surfaces of the first lens facing the object to be observed Ob and the eyepoint EP are aspheric. The aspheric surfaces have inflection points at which the curvature changes from positive to negative or from negative to positive in the peripheral area within the aperture.

[0180] The second lens L2 is a positive lens having a biconvex surface shape.

[0181] The third lens L3 is a negative meniscus lens with a concave surface facing the object to be observed Ob, and the lens surface of the third lens L3 facing the object to be observed Ob is aspheric.

[0182] The fourth lens L4 is a negative biconcave lens, and the lens surface of the fourth lens L4 facing the object to be observed Ob is aspheric.

[0183] The fifth lens L5 is a positive lens having a biconvex surface shape.

[0184] The sixth lens L6 is a biconvex positive lens, and both lens surfaces of the sixth lens L6 are aspherical.

[0185] Diopter adjustment is performed by moving the first lens L1 to the sixth lens L6 together along the optical axis.

[0186] In this example, the second lens L2 constitutes the first positive lens Lp1, and the fifth lens L5 constitutes the second positive lens Lp2. The fourth lens L4 constitutes the first negative lens Ln1, and the third lens L3 constitutes the second negative lens Ln2. The first lens L1 constitutes a lens La having an inflection point on its aspheric surface. The lens closest to the object to be observed is the first lens L1, and the lens closest to the eyepoint is the sixth lens L6.

[0187] Table 3 below shows the values ​​of each parameter in Example 3. The surface numbers in Table 3 correspond to the optical surfaces in Fig. 5. In Example 3, surfaces 1, 2, 5, 7, 11, and 12 are formed aspherically.

[0188] (Table 3) [Overall Specifications] fe = 18.131 TL = 34.466 ΣD = 27.290 ΣDair = 3.990 Daspe = 0.000 Daspo = 0.000 Np1 = 1.883 Np2 = 1.845 Nn1 = 1.636 Nn2 = 1.636 fLp1 = 20.863 fLp2 = 23.385 νp1 = 40.69 νp2 = 43.79 νn1 = 23.89 [Lens Specifications] Surface No. r D νd nd ∞ D0 *1 25.4960 3.790 55.71 1.535037 *2 -46.9438 0.100 3 56.3221 6.760 40.69 1.883000 4 -25.8347 2.910 *5 -9.8865 1.500 23.89 1.635500 6 -25.4576 0.780 *7 -21.2835 1.500 23.89 1.635500 8 64.5917 0.100 9 48.6079 6.750 43.79 1.848500 10 -31.3922 0.100 *11 21.8356 3.000 55.71 1.535037 *12 -590.5452 De EP [Aspherical Data] First Surface κ = 1.0000, A4 = -1.10743E-04, A6 = 6.01836E-07, A8 = -2.17619E-09 Second Surface κ = 1.0000, A4 = -1.10097E-05, A6 = 2.55575E-07, A8 = 0.00000E+00 Fifth Surface κ = 0.3380, A4 = 1.50503E-04, A6 = -2.10439E-07, A8 = 7.91597E-10 Seventh Surface κ = 1.0000, A4 = 7.74802E-06,A6=-2.58880E-08,A8=0.00000E+00 11th page κ=1.0000,A4=-5.30790E-05,A6=2.68087E-07,A8=-8.14673E-10 12th page κ=1.0000,A4=6.21114E-05,A6=6.22836E-08,A8=0.00000E+00 [Variable interval data] Diopter -1 [m. -1 ] 0[m -1 ] -4[m -1 ] +2[m -1 ] D0 6.8407 7.1763 5.7449 7.8080 De 24.0000 23.5710 25.2790 22.7810 [Lens group data] f1 31.454 f2 20.863 f3 -26.424 f4 -25.021 f5 23.385 f6 39.424

[0189] From the specifications shown in Table 3, it can be seen that the eyepiece optical system EL3 according to the third example satisfies conditional expressions (1) to (21).

[0190] FIG. 6 shows the diopter of the eyepiece optical system EL3 according to the third example, −1 [m -1 ] shows various aberration diagrams (spherical aberration, astigmatism, coma, distortion, and lateral chromatic aberration) at this time.

[0191] As is clear from the aberration diagrams shown in FIG. 6, the eyepiece optical system EL3 according to the third example effectively corrects various aberrations, particularly astigmatism and distortion, ensuring excellent optical performance.

[0192] Fourth Example The fourth example will be described with reference to Fig. 7, Fig. 8 and Table 4. As shown in Fig. 7, the eyepiece optical system EL (EL4) according to the fourth example comprises, arranged along the optical axis in order from the side of the observed object (image display element) Ob, a first lens L1 having positive refractive power, a cemented lens of a second lens L2 having negative refractive power and a third lens L3 having positive refractive power, a fourth lens having negative refractive power, a fifth lens having positive refractive power, and a sixth lens having positive refractive power.

[0193] The first lens L1 is a biconvex positive lens. The lens surface of the first lens facing the object to be observed Ob is aspheric. The aspheric surface has an inflection point at which the curvature changes from positive to negative or from negative to positive in the peripheral portion within the aperture.

[0194] The second lens L2 is a negative biconcave lens and is cemented to the third lens L3.

[0195] The third lens L3 is a biconvex positive lens and is cemented to the second lens L2.

[0196] The fourth lens L4 is a negative biconcave lens, and the lens surface of the fourth lens L4 facing the object to be observed Ob is aspheric.

[0197] The fifth lens L5 is a positive lens having a biconvex surface shape.

[0198] The sixth lens L6 is a biconvex positive lens, and the lens surface of the sixth lens L6 on the eyepoint side is aspherical.

[0199] Diopter adjustment is performed by moving the first lens L1 to the sixth lens L6 together along the optical axis.

[0200] In this example, the third lens L3 constitutes the first positive lens Lp1, and the fifth lens L5 constitutes the second positive lens Lp2. The fourth lens L4 constitutes the first negative lens Ln1, and the second lens L2 constitutes the second negative lens Ln2. The first lens L1 constitutes a lens La having an inflection point on its aspheric surface. The lens arranged closest to the object to be observed is the first lens L1, and the lens arranged closest to the eyepoint is the sixth lens L6.

[0201] Table 4 below shows the values ​​of each parameter in Example 4. The surface numbers in Table 4 correspond to the optical surfaces in Figure 7. In Example 4, surfaces 1, 6, and 11 are formed aspherical surfaces.

[0202] (Table 4) [Overall specifications] fe = 18.198 TL = 37.270 ΣD = 31.971 ΣDair = 3.579 Daspe = 0.000 Daspo = 0.000 Np1 = 1.883 Np2 = 1.849 Nn1 = 1.636 Nn2 = 1.593 fLp1 = 14.698 fLp2 = 24.181 νp1 = 40.69 νp2 = 43.79 νn1 = 23.89 [Lens specifications] Surface number r D νd nd ∞ D0 *1 45.1873 3.779 55.71 1.535037 2 -17.2217 0.100 3 -24.4573 1.000 35.27 1.592700 4 24.4824 7.792 40.69 1.883000 5 -23.4984 3.293 *6 -10.3072 1.200 23.89 1.635500 7 294.0016 0.100 8 113.3836 6.409 43.79 1.848500 9 -24.4012 0.086 10 66.5141 3.711 57.47 1.491755 *11 -26.6992 De EP [Aspherical data] Surface 1 κ=1.0000,A4=-1.55680E-04,A6=6.56284E-07,A8=-7.93249E-09 6th side κ=0.4463,A4=5.64814E-05,A6=2.63205E-07,A8=-8.15805E-10 Surface 11 κ=1.0000,A4=6.89637E-05,A6=-7.02689E-08,A8=6.89253E-11 [Variable interval data] Diopter -1 [m -1 ] 0[m -1] -4[m -1 ] +2[m -1 ] D0 4.626 5.2994 3.8799 5.9404 De 24.0000 23.7790 24.8600 23.4050 [Lens group data] f1 23.808 f2 -20.487 f3 14.698 f4 -15.646 f5 24.181 f6 39.258

[0203] From the specifications shown in Table 4, it can be seen that the eyepiece optical system EL4 according to the fourth example satisfies conditional expressions (1) to (21).

[0204] FIG. 8 shows the diopter of −1 [m -1 ] shows various aberration diagrams (spherical aberration, astigmatism, coma, distortion, and lateral chromatic aberration) at this time.

[0205] As is clear from the aberration diagrams shown in Figure 8, the eyepiece optical system EL4 of Example 4 effectively corrects various aberrations, particularly astigmatism and distortion, ensuring excellent optical performance.

[0206] Fifth Example The fifth example will be described with reference to Fig. 9, Fig. 10 and Table 5. As shown in Fig. 9, the eyepiece optical system EL (EL5) according to the fifth example comprises, arranged along the optical axis in order from the side of the observed object (image display element) Ob, a first lens L1 having positive refractive power, a cemented lens of a second lens L2 having negative refractive power and a third lens L3 having positive refractive power, a fourth lens having negative refractive power, a fifth lens having positive refractive power, and a sixth lens having positive refractive power.

[0207] The first lens L1 is a biconvex positive lens. The lens surface of the first lens facing the object to be observed Ob is aspheric. The aspheric surface has an inflection point at which the curvature changes from positive to negative or from negative to positive in the peripheral portion within the aperture.

[0208] The second lens L2 is a negative biconcave lens and is cemented to the third lens L3.

[0209] The third lens L3 is a biconvex positive lens and is cemented to the second lens L2.

[0210] The fourth lens L4 is a negative biconcave lens, and the lens surface of the fourth lens L4 facing the object to be observed Ob is aspheric.

[0211] The fifth lens L5 is a positive lens having a biconvex surface shape.

[0212] The sixth lens L6 is a biconvex positive lens, and both lens surfaces of the sixth lens L6 are aspherical.

[0213] Diopter adjustment is performed by moving the first lens L1 to the sixth lens L6 together along the optical axis.

[0214] In this example, the third lens L3 constitutes the first positive lens Lp1, and the fifth lens L5 constitutes the second positive lens Lp2. The fourth lens L4 constitutes the first negative lens Ln1, and the second lens L2 constitutes the second negative lens Ln2. The first lens L1 constitutes a lens La having an inflection point on its aspheric surface. The lens arranged closest to the object to be observed is the first lens L1, and the lens arranged closest to the eyepoint is the sixth lens L6.

[0215] Table 5 below shows the values ​​of each parameter in Example 5. The surface numbers in Table 5 correspond to the optical surfaces in Figure 9. In Example 5, surfaces 1, 6, 10, and 11 are formed aspherically.

[0216] (Table 5) [Overall Specifications] fe = 18.187 TL = 33.143 ΣD = 27.340 ΣDair = 3.512 Daspe = 0.000 Daspo = 0.000 Np1 = 1.883 Np2 = 1.849 Nn1 = 1.636 Nn2 = 1.593 fLp1 = 14.089 fLp2 = 22.186 νp1 = 40.69 νp2 = 43.79 νn1 = 23.89 [Lens Specifications] Surface No. r D νd nd ∞ D0 *1 40.8779 3.070 55.71 1.535037 2 -24.4309 0.100 3 -39.6584 1.000 35.27 1.592700 4 21.0259 8.341 40.69 1.883000 5 -24.7995 3.215 *6 -10.4525 1.200 23.89 1.635500 7 86.7881 0.100 8 55.0069 6.837 43.79 1.848500 9 -26.9863 0.097 *10 65.5311 3.380 57.47 1.491755 *11 -27.2455 De EP [Aspherical Data] First Surface κ = 1.0000, A4 = -1.42982E-04, A6 = 4.09497E-07, A8 = -4.87892E-09 Sixth Surface κ = 0.4467, A4 = 1.02764E-04, A6 = -1.82925E-07, A8 = 6.56706E-10 Tenth Surface κ = 1.0000, A4 = -8.63268E-05, A6 = 1.81967E-07, A8 = 0.00000E+00 Eleventh Surface κ = 1.0000, A4 = 1.24474E-05, A6 = -4.20778E-08,A8=4.75928E-10 [Variable interval data] Diopter -1 [m. -1 ] 0[m -1 ] -4[m -1 ] +2[m -1 ] D0 5.4662 5.8028 4.3814 6.4422 De 24.0000 23.7520 24.9640 23.3320 [Lens group data] f1 29.057 f2 -23.042 f3 14.089 f4 -14.610 f5 22.186 f6 39.610

[0217] From the specifications shown in Table 5, it can be seen that the eyepiece optical system EL5 according to the fifth example satisfies conditional expressions (1) to (21).

[0218] FIG. 10 shows the diopter of −1 [m -1 ] shows various aberration diagrams (spherical aberration, astigmatism, coma, distortion, and lateral chromatic aberration) at this time.

[0219] As is clear from the aberration diagrams shown in Figure 10, the eyepiece optical system EL5 of Example 5 effectively corrects various aberrations, particularly astigmatism and distortion, ensuring excellent optical performance.

[0220] Sixth Example The sixth example will be described with reference to Fig. 11, Fig. 12 and Table 6. As shown in Fig. 11, the eyepiece optical system EL (EL6) according to the sixth example comprises, arranged along the optical axis in order from the side of the observed object (image display element) Ob, a first lens L1 having positive refractive power, a second lens L2 having positive refractive power, a third lens L3 having negative refractive power, a fourth lens having negative refractive power, a fifth lens having positive refractive power, and a sixth lens having positive refractive power.

[0221] The first lens L1 is a biconvex positive lens. Both lens surfaces of the first lens L1 are aspherical. The aspherical surfaces have inflection points at which the curvature changes from positive to negative or from negative to positive in the peripheral portion within the aperture.

[0222] The second lens L2 is a positive meniscus lens with a concave surface facing the observed object Ob.

[0223] The third lens L3 is a negative meniscus lens with a concave surface facing the object to be observed Ob, and the lens surface facing the object to be observed Ob of the third lens L3 is aspheric.

[0224] The fourth lens L4 is a negative biconcave lens, and the lens surface of the fourth lens L4 facing the object to be observed Ob is aspheric.

[0225] The fifth lens L5 is a positive lens having a biconvex surface shape.

[0226] The sixth lens L6 is a positive meniscus lens with a convex surface facing the object under observation Ob, and the lens surface of the sixth lens L6 facing the object under observation Ob is aspheric.

[0227] Diopter adjustment is performed by moving the first lens L1 to the sixth lens L6 together along the optical axis.

[0228] In this example, the fifth lens L5 constitutes the first positive lens Lp1, and the second lens L2 constitutes the second positive lens Lp2. The third lens L3 constitutes the first negative lens Ln1, and the fourth lens L4 constitutes the second negative lens Ln2. The first lens L1 constitutes a lens La having an inflection point on its aspheric surface. The lens arranged closest to the object to be observed is the first lens L1, and the lens arranged closest to the eyepoint is the sixth lens L6.

[0229] Table 6 below shows the values ​​of each parameter in Example 6. The surface numbers in Table 6 correspond to the optical surfaces in Figure 11. In Example 6, surfaces 1, 2, 5, 7, and 11 are formed aspherically.

[0230] (Table 6) [Overall Specifications] fe = 18.187 TL = 34.863 ΣD = 27.814 ΣDair = 2.774 Daspe = 3.095 Daspo = 0.000 Np1 = 1.883 Np2 = 1.883 Nn1 = 1.636 Nn2 = 1.636 fLp1 = 17.100 fLp2 = 22.156 νp1 = 40.69 νp2 = 40.69 νn1 = 23.89 [Lens Specifications] Surface No. r D νd nd ∞ D0 *1 30.7427 3.453 55.71 1.535037 *2 -21.6928 0.111 3 -80.0537 6.330 40.69 1.883000 4 -16.3046 2.116 *5 -9.0760 1.500 23.89 1.635500 6 -44.0136 0.355 *7 -32.7012 1.500 23.89 1.635500 8 29.8046 0.092 9 30.5565 9.162 40.69 1.883000 10 -25.6532 0.100 *11 24.8745 3.095 54.89 1.677980 12 53.8481 De EP [Aspherical Data] First Surface κ = 1.0000, A4 = -2.33343E-04, A6 =23209E-05,A6=-1.63134E-08,A8=0.00000E+00 11th surface κ=1.0000,A4=-7.22449E-05,A6=9.01971E-08,A8=-1.60593E-10 [Variable interval data] Diopter -1 [m. -1 ] 0[m -1 ] -4[m -1 ] +2[m -1 ] D0 6.7120 7.0486 5.6270 7.6879 De 24.0000 23.7770 24.8540 23.3980 [Lens group data] f1 24.329 f2 22.156 f3 -18.297 f4 -24.310 f5 17.100 f6 65.366

[0231] From the specifications shown in Table 6, it can be seen that the eyepiece optical system EL6 according to the sixth example satisfies conditional expressions (1) to (21).

[0232] FIG. 12 shows the diopter of −1 [m -1 ] shows various aberration diagrams (spherical aberration, astigmatism, coma, distortion, and lateral chromatic aberration) at this time.

[0233] As is clear from the aberration diagrams shown in Figure 12, the eyepiece optical system EL6 of Example 6 effectively corrects various aberrations, particularly astigmatism and distortion, ensuring excellent optical performance.

[0234] Seventh Example The seventh example will be described with reference to Fig. 13, Fig. 14 and Table 7. The eyepiece optical system EL (EL7) according to the seventh example, as shown in Fig. 13, is composed of, arranged in order from the side of the observed object (image display element) Ob along the optical axis, a first lens L1 having positive refractive power, a second lens L2 having positive refractive power, a third lens L3 having negative refractive power, a fourth lens having positive refractive power, and a fifth lens having positive refractive power.

[0235] The first lens L1 is a biconvex positive lens. Both lens surfaces of the first lens L1 are aspherical. The aspherical surfaces have inflection points at which the curvature changes from positive to negative or from negative to positive in the peripheral portion within the aperture.

[0236] The second lens L2 is a positive meniscus lens with a concave surface facing the observed object Ob.

[0237] The third lens L3 is a negative biconcave lens, and the lens surface of the third lens L3 facing the object to be observed Ob is aspheric.

[0238] The fourth lens L4 is a positive lens having a biconvex surface shape.

[0239] The fifth lens L5 is a positive meniscus lens with a convex surface facing the object to be observed Ob, and both lens surfaces of the fifth lens L5 are aspherical.

[0240] Diopter adjustment is performed by moving the first lens L1 to the fifth lens L5 together along the optical axis.

[0241] In this example, the fourth lens L4 constitutes the first positive lens Lp1, and the second lens L2 constitutes the second positive lens Lp2. The third lens L3 constitutes the first negative lens Ln1. The first lens L1 constitutes a lens La having an inflection point on its aspheric surface. The lens closest to the object to be observed is the first lens L1, and the lens closest to the eyepoint is the fifth lens L5.

[0242] Table 7 below shows the values ​​of each parameter in Example 7. The surface numbers in Table 7 correspond to the optical surfaces in Figure 13. In Example 7, surfaces 1, 2, 5, 9, and 10 are formed aspherically.

[0243] (Table 7) [Overall Specifications] fe = 18.213 TL = 32.984 ΣD = 25.703 ΣDair = 2.748 Daspe = 0.000 Daspo = 0.000 Np1 = 1.883 Np2 = 1.883 Nn1 = 1.636 fLp1 = 16.698 fLp2 = 21.275 νp1 = 40.69 νp2 = 40.69 νn1 = 23.89 [Lens Specifications] Surface No. r D νd nd ∞ D0 *1 32.7975 3.029 55.71 1.535037 *2 -24.3942 0.494 3 -87.3421 6.489 40.69 1.883000 4 -15.9994 2.048 *5 -8.9544 3.025 23.89 1.635500 6 27.9672 0.106 7 28.7752 8.711 40.69 1.883000 8 -25.9469 0.100 *9 32.5952 1.701 55.71 1.535037 *10 184.2753 De EP [Aspherical Data] First Surface κ = 1.0000, A4 = -1.90801E-04, A6 = 8.52594E-07, A8 = -8.211896479E-08,A8=0.00000E+00 [Variable interval data] Diopter -1 [m. -1 ] 0[m -1 ] -4[m -1 ] +2[m -1 ] D0 6.9448 7.2819 5.8648 7.9248 De 24.0000 23.8000 24.7560 23.4570 [Lens group data] f1 26.638 f2 21.275 f3 -10.348 f4 16.698 f5 73.725

[0244] From the specifications shown in Table 7, it can be seen that the eyepiece optical system EL7 according to the seventh example satisfies the conditional expressions (1) to (7) and (9) to (19).

[0245] FIG. 14 shows the diopter of the eyepiece optical system EL7 according to the seventh example, −1 [m -1 ] shows various aberration diagrams (spherical aberration, astigmatism, coma, distortion, and lateral chromatic aberration) at this time.

[0246] As is clear from the aberration diagrams shown in Figure 14, the eyepiece optical system EL7 of Example 7 effectively corrects various aberrations, particularly astigmatism and distortion, ensuring excellent optical performance.

[0247] Next, the table of [Values ​​Corresponding to Conditional Expressions] is shown below, which summarizes the values ​​corresponding to each of the conditional expressions (1) to (21) for all the examples (Examples 1 to 7). Conditional expression (1) 1.700<Np1<2.050 Conditional expression (2) 1.700<Np2<2.050 Conditional expression (3) 0.90<Np2 / Np1<1.10 Conditional expression (4) 0.70<fLp1 / fe<1.30 Conditional expression (5) 0.90<fLp2 / fe<1.70 Conditional expression (6) 1.500<Nn1<1.700 Conditional expression (7) 16.000<νn1<36.000 Conditional expression (8) 1.500<Nn2<1.700 Conditional expression (9) 8.000<νp1-νn1<35.000 Conditional expression (10) 8.000<νp2−νn1<35.000 Conditional expression (11) 0.400<h / fe<0.500 Conditional expression (12) 0.000≦Daspe / ΣD<0.200 Conditional expression (13) 0.000≦Daspо / ΣD<0.200 Conditional expression (14) 0.20<y / Ry<0.85 Conditional expression (15) 20.000[mm]<De<30.000[mm] Conditional expression (16) 1.100<De / fe<1.500 Conditional expression (17) 0.250<D0 / fe<0.500 Conditional expression (18) 0.120<D0 / TL<0.250 Conditional expression (19) 0.080<ΣDair / ΣD<0.200 Conditional expression (20) 1.00< f1 / fe < 2.50 Conditional expression (21) 1.50 <fep / fe < 5.00

[0248] [Values ​​corresponding to conditional expressions] (Examples 1 to 7) Conditional Expression Example 1 Example 2 Example 3 Example 4 (1) 1.883 1.816 1.883 1.883 (2) 1.883 1.816 1.845 1.849 (3) 1.000 1.000 0.980 0.982 (4) 0.957 1.128 1.151 0.808 (5) 1.165 1.522 1.290 1.329 (6) 1.636 1.636 1.636 1.636 (7) 23.890 23.890 23.890 23.890 (8) 1.636 1.636 1.636 1.593 (9) 16.800 22.700 16.800 16.800 (10) 16.800 22.700 19.900 19.900 (11) 0.445 0.446 0.446 0.445 (12) 0.000 0.158 0.000 0.000 (13) 0.000 0.000 0.000 0.000 (14) 0.372 0.321 0.677 0.350 (15) 24.000 24.000 24.000 24.000 (16) 1.318 1.322 1.324 1.319 (17) 0.408 0.346 0.396 0.291 (18) 0.225 0.175 0.208 0.142 (19) 0.107 0.160 0.146 0.112 (20) 1.416 1.931 1.735 1.308 (21) 3.470 1.707 2.174 2.157 Conditional Expression 5th Example 6th Example 7th Example (1) 1.883 1.883 1.883 (2) 1.849 1.883 1.883 (3) 0.982 1.000 1.000 (4) 0.775 0.940 0.917 (5) 1.220 1.218 1.168 (6) 1.636 1.636 1.636 (7) 23.890 23.890 23.890 (8) 1.593 1.636 - (9) 16.800 16.800 16.800 (10) 19.900 16.800 16.800 (11) 0.445 0.445 0.444 (12) 0.000 0.111 0.000 (13) 0.000 0.000 0.000 (14) 0.369 0.324 0.358 (15) 24.000 24.000 24.000 (16) 1.320 1.320 1.318 (17) 0.319 0.388 0.400 (18) 0.175 0.202 0.221 (19) 0.128 0.100 0.107 (20) 1.598 1.338 1.463 (21) 2.178 3.594 4.048.

[0249] As described above, according to the present invention, it is possible to achieve an eyepiece optical system in which various aberrations (particularly astigmatism and distortion) are well corrected even when the finder magnification is high.

[0250] To make the present invention easier to understand, the present invention has been described with reference to the constituent elements of the embodiment, but it goes without saying that the present invention is not limited to these. The following content can be appropriately adopted within the scope that does not impair optical performance.

[0251] The lens surface may be spherical, flat, or aspherical. A spherical or flat lens surface is preferred because it facilitates lens processing and assembly adjustment and prevents degradation of optical performance due to errors in processing and assembly adjustment. It is also preferred because it minimizes degradation of imaging performance even when the image plane is misaligned. If the lens surface is aspherical, the aspherical surface may be any of the following aspherical surfaces: a ground aspherical surface, a glass-molded aspherical surface in which glass is molded into an aspherical shape, or a hybrid aspherical surface in which a resin is molded into an aspherical shape on the surface of glass. The lens surface may also be a diffractive surface, or the lens may be a gradient index lens (GRIN lens) or a plastic lens.

[0252] Each lens surface may be coated with an anti-reflection coating that has high transmittance over a wide wavelength range in order to reduce flare and ghosting and achieve high-contrast optical performance.

[0253] CAM Digital camera (optical equipment) OL Objective lens C Image pickup element Ob Image display element (observed object) EL (EL1 to EL7) Eyepiece optical system L1 First lens L2 Second lens L3 Third lens L4 Fourth lens L5 Fifth lens L6 Sixth lens EP Eye point

Claims

1. An eyepiece optical system having a first positive lens having positive refractive power and a second positive lens having positive refractive power, satisfying the following conditional equation. 1.700<Np1<2.050 1.700<Np2<2.050 However, Np1: refractive index of the first positive lens with respect to the d line Np2: Refractive index of the second positive lens with respect to the d line

2. An eyepiece optical system having at least five lenses and satisfying the following condition. 0.400<h / fe<0.500 However, fe: the combined focal length of the eyepiece optical system. h: Maximum object height of the object being observed by the eyepiece optical system.

3. The eyepiece optical system according to claim 1, wherein the first positive lens has the strongest positive refractive power in the eyepiece optical system and satisfies the following condition. 0.90<Np2 / Np1<1.10

4. The eyepiece optical system according to claim 1, wherein the first positive lens has the strongest positive refractive power in the eyepiece optical system and satisfies the following condition. 0.70<fLp1 / fe<1.30 However, fLp1: focal length of the first positive lens fe: Composite focal length of the eyepiece optical system

5. The eyepiece optical system according to claim 1, wherein the second positive lens has the second strongest positive refractive power in the eyepiece optical system and satisfies the following condition. 0.90<fLp2 / fe<1.70 However, fLp2: focal length of the second positive lens fe: Composite focal length of the eyepiece optical system

6. The eyepiece optical system according to claim 1, which has a first negative lens having the strongest negative refractive power in the eyepiece optical system, and satisfies the following conditional expression. 1.500<Nn1<1.700 16.000<νn1<36.000 However, Nn1: refractive index of the first negative lens with respect to the d line. νn1: Abbe number with reference to the d line of the first negative lens.

7. The eyepiece optical system according to claim 1, further comprising a second negative lens having the second strongest negative refractive power, and satisfying the following conditional expression. 1.500<Nn2<1.700 However, Nn2: refractive index of the second negative lens with respect to the d line.

8. The eyepiece optical system according to claim 6, satisfying the following conditional expression. 8.000<νp1-νn1<35.000 However, νp1: Abbe number with reference to the d line of the first positive lens. νn1: Abbe number with reference to the d line of the first negative lens.

9. The eyepiece optical system according to claim 6, satisfying the following conditional expression. 8.000<νp2−νn1<35.000 However, νp2: Abbe number with reference to the d line of the second positive lens. νn1: Abbe number with reference to the d line of the first negative lens.

10. An eyepiece optical system according to claim 1 or 2 that satisfies the following conditional expression. 0.400<h / fe<0.500 However, fe: the combined focal length of the eyepiece optical system. h: Maximum object height of the object being observed in the eyepiece optical system.

11. The eyepiece optical system according to claim 1 or 2, comprising at least one lens having an aspherical surface formed on its lens surface that satisfies the following condition. 0.000≦Daspe / ΣD<0.200 However, Daspe: the distance along the optical axis from the aspherical surface closest to the eye point among the aforementioned aspherical surfaces to the lens surface closest to the eye point of the eyepiece optical system. ΣD: Distance along the optical axis from the lens surface closest to the observed object to the lens surface closest to the eye point.

12. The eyepiece optical system according to claim 1 or 2, comprising at least one lens having an aspherical surface formed on its lens surface that satisfies the following condition. 0.000≦Daspо / ΣD<0.200 However, Daspo: the distance along the optical axis from the lens surface of the eyepiece optical system closest to the object being observed to the aspherical surface closest to the object being observed. ΣD: Distance along the optical axis from the lens surface closest to the observed object to the lens surface closest to the eye point.

13. An eyepiece optical system according to claim 1 or 2, having at least one lens on which an aspherical surface is formed, and an inflection point is provided on the aspherical surface where the radius of curvature reverses from positive to negative or from negative to positive, and satisfying the following conditional expression. 0.20<y / Ry<0.85 However, y: the distance between the optical axis of the lens and the inflection point in a direction perpendicular to the optical axis of the lens. Ry: Radius of the lens

14. An eyepiece optical system according to claim 1 or 2 that satisfies the following conditional expression. 20.000[mm]<De<30.000[mm] However, De: the distance along the optical axis from the lens surface closest to the eye point of the eyepiece optical system to the eye point.

15. An eyepiece optical system according to claim 1 or 2 that satisfies the following conditional expression. 1.100<De / fe<1.500 However, De: the distance along the optical axis from the lens surface closest to the eye point of the eyepiece optical system to the eye point. fe: Composite focal length of the eyepiece optical system

16. An eyepiece optical system according to claim 1 or 2 that satisfies the following conditional expression. 0.250<D0 / fe<0.500 However, D0: Diopter is 0 [m －1 The distance along the optical axis from the object being observed to the lens surface closest to the object being observed in [location] fe: Composite focal length of the eyepiece optical system

17. An eyepiece optical system according to claim 1 or 2 that satisfies the following conditional expression. 0.120<D0 / TL<0.250 However, D0: Diopter is 0 [m －1 The distance along the optical axis from the object being observed to the lens surface closest to the object being observed in [location] TL: Diopter is 0 [m] －１ The distance along the optical axis from the object being observed to the lens surface closest to the eye point in [location]

18. An eyepiece optical system according to claim 1 or 2 that satisfies the following conditional expression. 0.080<ΣDair / ΣD<0.200 However, ΣDair: The sum of the air gaps between lenses, from the lens closest to the object being observed to the lens closest to the eye point. ΣD: Distance along the optical axis from the lens surface closest to the observed object to the lens surface closest to the eye point.

19. An eyepiece optical system according to claim 1 or 2 that satisfies the following conditional expression. 1.00 < f1 / fe < 2.50 However, f1: the focal length of the lens positioned closest to the object being observed. fe: Composite focal length of the eyepiece optical system

20. An eyepiece optical system according to claim 1 or 2 that satisfies the following conditional expression. 1.50 <fep / fe< 5.00 However, fep: the focal length of the lens positioned closest to the eye point. fe: Composite focal length of the eyepiece optical system

21. The system comprises an objective lens, an image sensor for capturing an image formed by the objective lens, an image display element for displaying the image captured by the image sensor, and an eyepiece optical system for observing the image displayed on the image display element. An optical instrument characterized in that the eyepiece optical system is the eyepiece optical system described in claim 1 or 2.