JP4509192B2 - Macro lens and camera equipped with the same - Google Patents

Description

  The present invention relates to a macro lens and a camera including the macro lens, and is suitable for a silver salt or digital camera. In particular, the present invention relates to a macro lens suitable for an interchangeable lens applicable to a silver salt or digital single lens reflex camera.

  A number of macro lenses have been proposed as interchangeable lenses for single-lens reflex cameras or digital single-lens reflex cameras.

  In macro lenses, the variation in spherical aberration at infinite and short distances becomes large, so that a floating method in which a plurality of groups are moved has been adopted for focusing.

  Many of the conventional macro lenses emphasize a design that balances infinity and short distance and has a magnification of about 1/10. Therefore, the performance at infinite photographing is inferior to a general lens system that is not a macro lens.

  In focusing, spherical aberrations and field curvature fluctuations from infinity to short distances are large, and many of these aberrations are suppressed using floating.

  However, when a large-aperture lens is used, it becomes difficult to suppress these fluctuations, and in particular, field curvature and coma become large in a short distance range.

  The present invention has been made in view of such problems of the prior art, and an object of the present invention is to provide a bright macro lens with good aberration correction even at a short distance and a camera including the same.

  Furthermore, it is to realize a large-aperture macro lens with an F number of about 1.8 while suppressing aberration fluctuations from infinity to a short distance.

  Furthermore, the present invention assumes an image circle having a half size and a diagonal length of about half of the 135 format as a film size, and another object is to provide an optimum macro lens for the image circle.

  The macro lens of the present invention that achieves the above object is composed of, in order from the object side, a first lens group having a positive power, a second lens group having a negative power, and a third lens group having a positive power. A negative meniscus lens with a concave surface on the object side is placed closest to the object side, and when focusing from the object point at infinity to the closest object point, the distance between each lens group is changed and moved independently to the object side. It is a feature.

  Hereinafter, the reason and effect | action which take said structure in this invention are demonstrated.

  First, the macro lens of the present invention can be used for all cameras. In particular, the macro lens is optimal for a single-lens reflex camera (regardless of whether the lens is changed) that requires a back focus for providing a mechanism for dividing the observation optical path. Moreover, it can be used not only for cameras for silver salt films but also for cameras using electronic image sensors such as solid-state image sensors (CCD).

  Now, the macro lens of the present invention is composed of two positive lens groups, and each is independently moved to correct the aberration at the time of focusing at a short distance by a floating action.

  By the way, a macro lens for a single-lens reflex camera must ensure a predetermined back focus distance for lens replacement. Although the angle of view is a medium telephoto lens system of about 2ω≈24 °, the image circle is small, so the lens focal length is about half that of the angle of view compared to the 135 format. For this reason, in the lens system according to the specification of the present invention, it is not easy to ensure the back focus.

  In order to secure this back focus, the first lens on the most object side in the positive first group needs to be a negative lens. Further, in order to bring the principal point position to the rear side and the image side of the lens system, it is desirable that the first lens is a negative meniscus lens having a concave surface facing the object side. With this configuration, a sufficient back focus distance can be obtained, so that a space for the quick return mirror can be secured.

  From the above, the macro lens according to the present invention includes, in order from the object side, the first lens group having a positive power, the second lens group having a negative power, and the third lens group having a positive power. The first lens group has a concave surface on the object side. The negative meniscus lens is arranged closest to the object side, and when focusing from the object point at infinity to the closest object point, the distance between the lens groups is changed and moved to the object side independently.

  In this case, by using three lens groups of positive, negative, and positive, the power distribution of the substantially symmetrical system is achieved, and the aberration at the time of focusing at a short distance is corrected by the floating action by moving each independently. Yes.

  That is, in order to improve near-field performance and suppress aberration fluctuations from infinity to short distance, it is preferable to move the three lens groups positive, negative, and positive during focusing to float. With this configuration, fluctuations in spherical aberration and coma during focusing can be minimized. Furthermore, it becomes easier to correct fluctuations in field curvature.

  However, with respect to the lens frame structure, the two-group configuration is overwhelmingly advantageous, so that the variation in performance due to manufacturing errors can be made considerably smaller than the three-group configuration.

  In the case of the above-described two-group configuration, it is desirable to arrange the diaphragm in the first group, and in the case of the three-group configuration, the diaphragm is arranged in the second group.

  The marginal ray height takes the minimum value because it is in the first group in the case of the two-group configuration and in the second group in the case of the three-group configuration. At that position, the aperture diameter is small and the aperture itself can be made compact. Further, at this position, the marginal ray takes a minimum value and becomes a substantially afocal ray, so that there is almost no influence even if the iris moves back and forth due to an attachment error of the iris position.

  Further, it is desirable to include a plurality of positive lenses between the negative meniscus lens and the stop.

  In the first group, it is desirable to arrange at least two positive lenses after the first lens. In order to correct spherical aberration in the first group, positive refractive power is required, but in order to correct this well, at least two positive lenses are required. In addition, with this configuration, it is not necessary to increase the diameter of the diaphragm disposed behind these lenses more than necessary.

  In addition, it is desirable that the lenses immediately before and after the stop be negative lenses.

  If the front and rear of the aperture are negative lenses, the configuration is relatively symmetric about the aperture. Therefore, it is advantageous for correcting distortion.

  In the case of a two-group configuration, the configuration of the first group, the configuration of the first group and the second group in the case of a three-group configuration, a negative meniscus lens having a concave surface on the object side, and a positive lens in order from the object side Group, positive lens whose object side surface has a smaller radius of curvature than the image side surface, negative lens whose object side surface has a smaller absolute value of curvature radius than the object side surface, aperture, object side surface curvature than the image side surface It is desirable to have a negative lens having a surface having a small radius and a positive lens having a surface having a smaller radius of curvature than the object side.

  This employs a so-called Gauss type. At this time, in order to converge the diverging light of the first lens little by little and make it incident on the subsequent negative lens, a positive lens group and a positive lens having a surface whose object side surface has a smaller absolute value of the radius of curvature than the image side surface are provided. ing.

  Various aberrations are corrected by a strong negative power air lens sandwiching the apertures of two negative lenses.

  The subsequent positive lens maintains the symmetry of the Gauss type optical system, and also adjusts the incident angle to the subsequent second group (the third group in the case of the three-group configuration) and increases the beam diameter. It prevents that.

  The lens to be used may be a single lens or a cemented lens, and may be constructed by cementing adjacent lenses. However, since the aberration correction can be satisfactorily performed by adopting a gauss type, other than the final lens group (two-group construction) In this case, it is preferable that all the first group and the second group in the case of the first group and the third group are single lenses, and the manufacturing cost is suppressed.

  In addition, it is desirable that the configuration of the second group in the case of the 2-group configuration, and the configuration of the third group in the case of the 3-group configuration have a cemented positive lens in which a positive lens and a negative lens are cemented.

  The final lens group (the second group in the case of the two-group configuration, the third group in the case of the three-group configuration) is preferably configured with a small number of lenses in order to shorten the total lens length, but a cemented positive lens is used. Accordingly, it is possible to correct the aberration with a small number of lenses, which is more preferable.

  In addition, this configuration, when forming an image on the light receiving surface of the electronic image sensor, requires a smaller incident angle of the off-axis principal ray with respect to the light receiving surface. is doing.

  In order to satisfactorily correct chromatic aberration, it is desirable to dispose at least one positive lens and one negative lens in the final group. Moreover, the effect is further increased by bonding these lenses.

  Next, more preferable numerical conditions in the above configuration will be described.

  It is desirable that the focal length of the first lens satisfies the following conditional expression.

-4 <f _F / f _L <-1 (1)
Here, f _F is the focal length of the negative meniscus lens closest to the object side, and f _L is the focal length of the entire system when focusing on an object point at infinity.

  If the upper limit of -1 in conditional expression (1) is exceeded, the power of this lens becomes too strong, and spherical aberration, coma aberration, curvature of field and all other aberrations become large, and correction with other lenses becomes difficult. . Also, if the lower limit of −4 is exceeded, the lens power becomes weak, and it becomes difficult to ensure a sufficient back focus.

  Further, by limiting the upper and lower limits as in the following conditional expression, the above effect can be further obtained.

−2.5 <f _F / f _L <−1.8 (1) ′
Further, it is desirable that the first lens satisfies the following conditional expression.

−12.5 <(r ₁ + r ₂ ) / (r ₁ −r ₂ ) <− 0.85 (2)
Here, r ₁ is the radius of curvature of the object side surface of the negative meniscus lens closest to the object side, and r ₂ is the radius of curvature of the image side surface of the negative meniscus lens closest to the object side.

  If the lower limit of −12.5 of the conditional expression (2) is exceeded, the negative refractive power becomes weak, so that it is difficult to ensure the back focus as in the conditional expression (1). On the other hand, if the upper limit of -0.85 in conditional expression (2) is exceeded, the negative refractive power of the first surface becomes too strong, and the variation in spherical aberration from infinity to the nearest becomes large, which is not preferable.

  More desirably, it is desirable to limit the lower limit of conditional expression (2) as follows.

−8.5 <(r ₁ + r ₂ ) / (r ₁ −r ₂ ) <− 0.85 (2) ′
In a large-aperture lens system, particularly under F1.8, it becomes difficult to correct spherical aberration and coma. Therefore, in order to secure a large aperture F-number, it is desirable to set the focal length of the first group within the following range in the two-group configuration.

0.5 <f ₁ / f _L <1.8 (3-1)
Here, f ₁ is the focal length of the first lens group, and f _L is the focal length of the entire system when focusing on an object point at infinity.

  Similarly, in the three-group configuration, it is desirable to set the focal length of the first group within the following range.

0.5 <f ₁ / f _L <1.8 (3-2)
Here, f ₁ is the focal length of the first lens group, f ₃ is the focal length of the third lens group, and f _L is the focal length of the entire system when focusing on an object point at infinity.

  When the power of the first lens group is increased beyond the lower limit of 0.5 of the conditional expression (3-1) or (3-2), the axial marginal ray is greatly refracted at a bright F number, and at an infinite object point. Correction of spherical aberration becomes difficult. If the upper limit of 1.8 to these conditional expressions is exceeded, the lens system will be enlarged.

  Furthermore, in order to correct spherical aberration at an infinite object point more satisfactorily, in the second group configuration, the refractive power of the first group is further weakened, and conditional expression (3-1) ′ is changed to the third group configuration. Preferably satisfies the conditional expression (3-2) ′ by increasing the refractive power of the first unit.

1.0 <f ₁ / f _L <1.8 (3-1) ′
0.5 <f ₁ / f _L <1.0 (3-2) ′
If the lower limit of these conditional expressions is within the range of 1.0 or 0.5, a brighter lens system with higher performance can be realized.

  Focusing can be sufficiently achieved by making the lens configuration into two groups and moving each group to float. However, the curvature of spherical aberration at a short distance tends to be large. In order to minimize this, it is desirable to set the focal length of the most image side group within the range of the following conditional expression.

1.8 <f ₂ / f _L <3.5 (4-1)
Here, f ₂ is the focal length of the second lens group, and f _L is the focal length of the entire system when focusing on an object point at infinity.

  Similarly, in the three-group configuration, it is desirable to set the focal length of the third group within the following range.

1.8 <f ₃ / f _L <3.5 (4-2)
Here, f ₃ is the focal length of the third lens group, and f _L is the focal length of the entire system when focusing on an object point at infinity.

  When the lower limit of 1.8 to these conditional expressions is exceeded, performance degradation such as spherical aberration and field curvature at a short distance increases. If the upper limit of 3.5 to these conditional expressions is exceeded, the amount of movement of the second group or the third group during focusing increases, which is not preferable.

  Furthermore, conditional expressions (4-1) and (4-2) may be limited as follows.

2.2 <f ₂ / f _L <3.0 (4-1) ′
2.2 <f ₃ / f _L <3.0 (4-2) ′
Within the range of these conditional expressions, the above effects can be further obtained.

  By placing the focal length of each group as described above, emphasis is placed on infinite design, and even if it is designed so that infinite performance is not inferior to that of ordinary lenses, it will ensure sufficient short-range performance. Can do.

  Moreover, it is desirable for the large-aperture macro lens to satisfy the following conditional expression.

-1.0 <MG <-0.4 (5)
7 ° <SW <16 ° (6)
1.0 <F <3.0 (7)
However, MG is the maximum imaging magnification, SW is the incident half angle of view of the diagonal ray incident on the maximum image height in the imaging range of the camera body when focusing on infinity, and the imaging range of the imaging surface can be arbitrarily changed In this case, it is the maximum value of the possible range, and F is the F number when focusing on an object point at infinity and when the aperture is opened.

  For the macro lens, it is desirable that the maximum photographing magnification satisfies the conditional expression (5). The macro lens requires a magnification of about -0.4, which is the upper limit. Further, in order to achieve a lower magnification of −1.0 or less, the number of lenses must be increased or the F-number must be increased.

  Also, if the upper limit of 16 ° of conditional expression (6) is exceeded, the photographing range is widened, so that it is difficult to take a photograph with a large photographing magnification unless it is very close to the subject. If it is within the range of this conditional expression, a photograph with a large magnification can be easily taken if it is close to the subject. If the lower limit of 7 ° is exceeded, the lens system has a long focal length, so that the entire lens length becomes long and it is difficult to reduce the size of the lens system.

  Furthermore, in a lens system that exceeds the range of conditional expression (7), it is not very suitable to be called a large aperture lens. In particular, anomalous dispersion glass is preferably used in order to satisfy the conditional expression (7).

  Further, the upper limit of 3.0 in the conditional expression (7) is limited as follows, so that a brighter lens system is obtained. In the case of a large-diameter lens, it is desirable that the upper limit of the following conditional expression is 2.0 than conditional expression (7).

1.0 <F <2.0 (7) ′
As in the lens system of the present invention, when the photographing magnification is as large as about 0.5 times, even if the aberration of the design reference wavelength can be corrected, the performance deterioration due to chromatic aberration becomes large. In the present invention, an anomalous dispersion glass is used on the rear side of the stop to correct axial chromatic aberration and lateral chromatic aberration, thereby realizing a large aperture lens with a large photographing magnification.

  As described above, focusing is performed by moving each group independently. At this time, it is desirable that the movement amount of the first group be in the following range.

0.4 <Δd ₁ / f _L <0.8 (8)
However, Δd ₁ is the amount of extension of the first lens group from the time of focusing on an object point at infinity to the time of focusing on the closest object point, and f _L is the focal length of the entire system when focusing on an object point at infinity.

  The power of the first group is defined by the conditional expressions (3-1) and (3-2). When the power is within this range, the feed amount of 0.4 or more which is the lower limit of the conditional expression (8) is It becomes necessary. Below the lower limit of the conditional expression, photographing within the upper limit range of the conditional expression (5) cannot be performed, which is not sufficient as a macro lens. If the upper limit of 0.8 in conditional expression (8) is exceeded, the macro shooting magnification is sufficient, but the movement amount becomes large, which is not preferable in terms of mechanical configuration.

  In the lens system of the present invention, it is desirable to satisfy the following conditional expression.

13 mm>IH> 10 mm (9)
3.5> f _b / IH (10)
Here, IH is the image circle radius when focusing on an object point at infinity, and f _b is the back focus of the lens system when focusing on an object point at infinity.

  These conditional expressions are conditional expressions for a space necessary for arranging a quick return mirror or the like. Conditional expression (9) is an assumed image circle radius. At this time, the dimension necessary for securing the space for placing the mirror on the layout is within the range of conditional expression (10). If the lower limit of 10 mm of the conditional expression (9) is exceeded, the mirror space becomes insufficient. If the upper limit of 13 mm of the conditional expression (9) is exceeded, the camera body becomes too large.

  Furthermore, in the lens system of the present invention, it is desirable that the following conditional expression is satisfied.

1 ° <| EW | <11 ° (11)
However, EW is the angle formed by the light beam emitted from the diagonal principal ray incident on the maximum image height on the imaging surface of the camera body when focusing on an object point at infinity, and the imaging range on the imaging surface can be changed arbitrarily. If possible, it is the value at the maximum image height within the possible range.

  Since the lens system of the present invention can be applied to a digital camera, the incident angle to an image pickup device such as a CCD becomes a problem. If the incident angle to the CCD or the like is too large, there is a concern that the amount of light is insufficient due to oblique incidence. In particular, when the image height is increased, the exit angle of the lens system is increased, so that the peripheral dimming by the CCD or the like is increased. Conditional expression (11) is required in order to minimize the drop in the amount of light due to the peripheral dimming. Conditional expression (11) is the absolute value of the angle formed by the emitted light of the diagonal principal ray and the optical axis, that is, the emission angle of the diagonal principal ray. In the CCD or the like when used in the lens system of the present invention, the oblique incident characteristics of the CCD or the like are matched to the lens system. It is desirable that the incident angle of the diagonal chief ray to the CCD or the like, that is, the emission angle of the optical system does not exceed the range of the conditional expression (11).

  The macro lens of the present invention can be used for a silver salt film camera and a camera using an electronic image sensor such as a solid-state image sensor (CCD). In addition, a mount (screw type, bayonet type, etc.) can be provided so that the macro lens and the camera body can be attached and detached. At that time, it is preferable that the incident half angle of view of the diagonal ray satisfies the above condition (6).

  According to the present invention, it is possible to provide a macro lens having an F number of 1.8 and a large aperture, in which various aberrations are favorably corrected from infinity to a short distance.

  Examples 1 to 3 of the macro lens of the present invention will be described below. Here, Examples 1-2 are reference examples. FIGS. 1 to 3 show lens cross-sectional views of Examples 1 to 3 when focusing on an object point at infinity (a) and at a magnification of −0.52 (a), respectively. In the figure, the first lens group is indicated by G1, the second lens group is indicated by G2, the third lens group is indicated by G3, the stop is indicated by S, and the image plane is indicated by I.

  FIG. 1 shows a macro lens of Example 1 of the present invention. The first lens group G1 includes, in order from the object side, a first lens of a negative meniscus lens having a concave surface facing the object side, a second lens of a positive meniscus lens having a concave surface facing the object side, and a third lens of a biconvex positive lens. A fourth lens of a positive meniscus lens having a convex surface facing the object side, a fifth lens of a biconcave negative lens, a stop, a sixth lens of a biconcave negative lens, and a positive meniscus lens having a convex surface facing the image surface side. The second lens group consists of a negative meniscus lens with a concave surface facing the image surface, a negative meniscus lens with a concave surface facing the image surface, and a biconvex lens. The positive lens is composed of a tenth lens of a cemented positive lens.

  Focusing to a short-distance object point is performed by moving the first lens group and the second lens group to the object-pair side.

  In this embodiment, the image height IH is 11.1 mm, and the CCD pixels arranged on the image plane I have a pitch of 5.5 μm.

  FIG. 2 shows a macro lens of Example 2 of the present invention. The first lens group G1, in order from the object side, has a first lens of a negative meniscus lens having a concave surface facing the object side, a second lens of a positive meniscus lens having a concave surface facing the object side, and a convex surface facing the object side. The third lens of the positive meniscus lens, the fourth lens of the positive meniscus lens with the convex surface facing the object side, the fifth lens of the biconcave negative lens, the stop, the sixth lens of the biconcave negative lens, and the convex surface facing the image surface side The seventh lens of the positive meniscus lens and the eighth lens of the biconvex positive lens, the second lens group has the ninth lens of the negative meniscus lens with the concave surface facing the image surface side, and the concave surface facing the image surface side It is composed of a tenth lens which is a cemented positive lens composed of a negative meniscus lens and a biconvex positive lens.

  Focusing to a short-distance object point is performed by moving the first lens group and the second lens group to the object-pair side.

  In this embodiment, the image height IH is 11.1 mm, and the CCD pixels arranged on the image plane I have a pitch of 5.5 μm.

  FIG. 3 shows a macro lens of Example 3 of the present invention. The first lens group G1 includes, in order from the object side, a first lens of a negative meniscus lens having a concave surface facing the object side, a second lens of a positive meniscus lens having a concave surface facing the object side, and a third lens of a biconvex positive lens. The lens is composed of a fourth lens of a positive meniscus lens having a convex surface facing the object side. The second lens group includes a fifth lens of a biconcave negative lens, an aperture, a sixth lens of a biconcave negative lens, and a convex surface on the image surface side. The seventh lens of the positive meniscus lens facing the lens and the eighth lens of the biconvex positive lens. The third lens group has a ninth lens of the negative meniscus lens with the concave surface facing the image surface and a concave surface facing the image surface. It is composed of a tenth lens of a cemented positive lens composed of a directed negative meniscus lens and a biconvex positive lens.

  Focusing to a short-distance object point is performed by moving the first lens group, the second lens group, and the third lens group to the object-pair side.

  In this embodiment, the image height IH is 11.1 mm, and the CCD pixels arranged on the image plane I have a pitch of 5.5 μm.

The numerical data of each of the above embodiments are shown below. Symbols are the above, f _L is the focal length of the entire system when focusing on an object point at infinity, F _NO is the F number, M is the magnification, r ₁ , r ₂ ... is the radius of curvature of each lens surface, d ₁ , d ₂ ... are the distances between the lens surfaces, n _d1 , n _d2 ... are the refractive indices of the d-line of each lens, and ν _d1 , ν _d2 . Abbe number.

Example 1
r ₁ = -35.629 d ₁ = 2.00 n _d1 = 1.64769 ν _d1 = 33.79
r ₂ = -74.905 d ₂ = 0.94
r ₃ = -702.420 d ₃ = 4.03 n _d2 = 1.77250 ν _d2 = 49.60
r ₄ = -49.343 d ₄ = 0.10
r ₅ = 45.810 d ₅ = 5.06 n _d3 = 1.72916 ν _d3 = 54.68
r ₆ = -809755.657 d ₆ = 0.10
r ₇ = 26.150 d ₇ = 2.80 n _d4 = 1.52249 ν _d4 = 59.84
r ₈ = 32.770 d ₈ = 5.55
r ₉ = -311.668 d ₉ = 1.41 n _d5 = 1.59551 ν _d5 = 39.24
r ₁₀ = 21.286 d ₁₀ = 3.13
r ₁₁ = ∞ (aperture) d ₁₁ = 3.08
r ₁₂ = -21.101 d ₁₂ = 1.35 n _d6 = 1.58144 ν _d6 = 40.75
r ₁₃ = 93.106 d ₁₃ = 1.30
r ₁₄ = -323.070 d ₁₄ = 4.50 n _d7 = 1.49700 ν _d7 = 81.54
r ₁₅ = -30.291 d ₁₅ = 0.30
r ₁₆ = 56.785 d ₁₆ = 4.54 n _d8 = 1.77250 ν _d8 = 49.60
r ₁₇ = -56.785 d ₁₇ = (variable)
r ₁₈ = 5517.326 d ₁₈ = 1.52 n _d9 = 1.51742 ν _d9 = 52.43
r ₁₉ = 38.046 d ₁₉ = 1.93
r ₂₀ = 91.845 d ₂₀ = 1.55 n _d10 = 1.76182 ν _d10 = 26.52
r ₂₁ = 40.260 d ₂₁ = 4.87 n _d11 = 1.74100 ν _d11 = 52.64
r ₂₂ = -60.775 d ₂₂ = (variable)
r ₂₃ = ∞ (image plane)
f _L 51.000
F _NO 1.83
M -1 / ∞ -0.1 -0.52
d ₁₇ 0.50 2.08 8.02
d ₂₂ 35.18 39.37 58.83.

(Example 2)
r ₁ = -35.941 d ₁ = 2.00 n _d1 = 1.64769 ν _d1 = 33.79
r ₂ = -70.445 d ₂ = 1.40
r ₃ = -910.133 d ₃ = 3.99 n _d2 = 1.77250 ν _d2 = 49.60
r ₄ = -51.742 d ₄ = 0.10
r ₅ = 43.701 d ₅ = 4.34 n _d3 = 1.72916 ν _d3 = 54.68
r ₆ = 3929264.108 d ₆ = 0.10
r ₇ = 24.021 d ₇ = 2.80 n _d4 = 1.52249 ν _d4 = 59.84
r ₈ = 28.431 d ₈ = 5.16
r ₉ = -861.896 d ₉ = 1.30 n _d5 = 1.59551 ν _d5 = 39.24
r ₁₀ = 19.550 d ₁₀ = 3.31
r ₁₁ = ∞ (aperture) d ₁₁ = 5.78
r ₁₂ = -20.465 d ₁₂ = 1.35 n _d6 = 1.58144 ν _d6 = 40.75
r ₁₃ = 99.536 d ₁₃ = 0.91
r ₁₄ = -257.770 d ₁₄ = 4.50 n _d7 = 1.49700 ν _d7 = 81.54
r ₁₅ = -28.944 d ₁₅ = 0.30
r ₁₆ = 53.287 d ₁₆ = 6.17 n _d8 = 1.77250 ν _d8 = 49.60
r ₁₇ = -59.475 d ₁₇ = (variable)
r ₁₈ = -17636653.385 d ₁₈ = 1.38 n _d9 = 1.51742 ν _d9 = 52.43
r ₁₉ = 36.329 d ₁₉ = 1.73
r ₂₀ = 96.180 d ₂₀ = 1.68 n _d10 = 1.76182 ν _d10 = 26.52
r ₂₁ = 40.845 d ₂₁ = 4.86 n _d11 = 1.74100 ν _d11 = 52.64
r ₂₂ = -53.026 d ₂₂ = (variable)
r ₂₃ = ∞ (image plane)
f _L 51.009
F _NO 1.83
M -1 / ∞ -0.1 -0.52
d ₁₇ 0.50 1.71 6.79
d ₂₂ 35.06 39.46 58.75.

(Example 3)
r ₁ = -37.956 d ₁ = 1.52 n _d1 = 1.64769 ν _d1 = 33.79
r ₂ = -83.532 d ₂ = 1.00
r ₃ = -534.319 d ₃ = 4.08 n _d2 = 1.77250 ν _d2 = 49.60
r ₄ = -51.466 d ₄ = 0.10
r ₅ = 42.553 d ₅ = 5.08 n _d3 = 1.72916 ν _d3 = 54.68
r ₆ = -171439725.185 d ₆ = 0.10
r ₇ = 25.634 d ₇ = 2.80 n _d4 = 1.52249 ν _d4 = 59.84
r ₈ = 31.696 d ₈ = (variable)
r ₉ = -296.224 d ₉ = 1.30 n _d5 = 1.59551 ν _d5 = 39.24
r ₁₀ = 20.553 d ₁₀ = 3.13
r ₁₁ = ∞ (aperture) d ₁₁ = 3.08
r ₁₂ = -21.557 d ₁₂ = 1.35 n _d6 = 1.58144 ν _d6 = 40.75
r ₁₃ = 102.583 d ₁₃ = 1.21
r ₁₄ = -308.613 d ₁₄ = 4.50 n _d7 = 1.49700 ν _d7 = 81.54
r ₁₅ = -30.433 d ₁₅ = 0.30
r ₁₆ = 53.387 d ₁₆ = 4.51 n _d8 = 1.77250 ν _d8 = 49.60
r ₁₇ = -61.253 d ₁₇ = (variable)
r ₁₈ = 116624.465 d ₁₈ = 1.38 n _d9 = 1.51742 ν _d9 = 52.43
r ₁₉ = 36.250 d ₁₉ = 1.94
r ₂₀ = 83.298 d ₂₀ = 1.20 n _d10 = 1.76182 ν _d10 = 26.52
r ₂₁ = 38.827 d ₂₁ = 4.19 n _d11 = 1.74100 ν _d11 = 52.64
r ₂₂ = -61.075 d ₂₂ = (variable)
r ₂₃ = ∞ (image plane)
f _L 51.000
F _NO 1.83
M -1 / ∞ -0.1 -0.52
d ₈ 5.57 5.55 5.18
d ₁₇ 0.50 2.09 8.17
d ₂₂ 35.19 39.41 59.67.

FIGS. 4 to 6 show aberration diagrams when focusing on infinity in Examples 1 to 3 (a) and focusing to -0.52 (b), respectively. In these aberration diagrams, “SA” indicates spherical aberration, “AS” indicates astigmatism, “DT” indicates distortion, and “CC” indicates lateral chromatic aberration. In each aberration diagram, “IH” indicates the image height. Next, the values of the conditions (1) to (11) in the above embodiments will be shown. However, conditions (3) and (4) mean conditions (3-1) or (3-2), (4-1) or (4-2), respectively.
Example 1 2 3
(1) -2.10 -2.27 -2.13
(2) -2.81 -3.08 -2.63
(3) 1.26 1.30 0.70
(4) 2.71 2.45 2.71
(5) -0.52 -0.52 -0.52
(6) 13.3 13.3 13.3
(7) 1.83 1.83 1.83
(8) 0.61 0.59 0.62
(9) 11.1 11.1 11.1
(10) 3.15 3.15 3.16
(11) 9.45 7.97 9.68.

  As described above, the macro lens of the present invention described above can be applied to a silver salt or digital single lens reflex camera. These are exemplified below.

  FIG. 7 shows a silver salt type single-lens reflex camera using the macro lens of the present invention as a photographing lens. In FIG. 7, reference numeral 10 denotes a single-lens reflex camera, 2 denotes a photographing lens, and 4 denotes a mount portion that allows the photographing lens 2 to be attached to and detached from the single-lens reflex camera 10, and is a screw type mount or bayonet type mount (see FIG. 7). In this case, a bayonet type mount is used). Further, 6 is a film, 11 is a quick return mirror disposed between the lens system 2 on the optical path 3 of the photographing lens 2 and the film 6, 12 is a finder screen disposed in the optical path reflected from the quick return mirror, and 13 Is a pentaprism, 14 is a viewfinder, and E is an observer's eye (eye point). The macro lens of the present invention is used as the photographing lens 2 of the single-lens reflex camera 10 having such a configuration.

  Next, FIG. 8A shows a conceptual diagram of a configuration in which the macro lens of the present invention is incorporated in an objective optical system of a digital single-lens reflex camera. In this example, the objective optical system 21 is shown using the macro lens of Example 1. The imaging light beam passing through the objective optical system 21 is separated into a photographing optical path and a finder optical path through a half mirror prism (beam splitter or the like) 22 disposed on the back focus side. Note that it is desirable to use a quick return mirror instead of the half mirror prism 22 to prevent loss of light quantity. Further, a filter F such as a low-pass filter and an infrared cut filter and the CCD 23 are arranged in the photographing optical path, and an object image is formed on the imaging surface of the CCD 23 through the filter F. In the finder optical path, a screen mat 24 is disposed on a primary image surface formed at a position conjugate with the imaging surface, and this primary image is reflected by the plane mirror 25 and 2 by the relay optical system 26. While being relayed as the next image, the image is erect. Then, the secondary image is guided to the observation image eyeball E by the eyepiece lens 27.

  In the viewfinder optical path portion of FIG. 8A, the plane mirror 25 and the relay optical system 26 may be replaced with a concave mirror prism 28 having a positive power, as shown in FIG. 8B. With such a configuration, the number of parts can be reduced and downsizing can be realized. The concave mirror prism 28 may have power on the entrance surface and the exit surface, and the reflection surface may be a rotationally symmetric surface (spherical surface, aspheric surface, etc.), non-anamorphic surface, free curved surface, etc. It may be a rotationally symmetric surface. Moreover, it may replace with CCD23 and may be comprised as a silver salt camera which has arrange | positioned the silver salt film.

  The above-described macro lens of the present invention and a camera including the macro lens can be configured as follows, for example.

    [1] In order from the object side, a first lens unit having a positive power and a second lens group having a positive power are arranged. The first lens unit has a negative meniscus lens having a concave surface on the object side closest to the object side. A macro lens, wherein the distance between the first lens group and the second lens group is changed and moved independently toward the object side during focusing from the object point in-focus to the closest object point.

    [2] The macro lens according to [1], wherein a diaphragm is disposed in the first lens group.

    [3] The macro lens according to claim 2, comprising a plurality of positive lenses between the negative meniscus lens and the stop.

    [4] The macro lens according to claim 2 or 3, wherein the lens immediately before and after the stop is a negative lens.

    [5] The positive first lens group includes, in order from the object side, a negative meniscus lens having a concave surface on the object side, a positive lens group, a positive lens having an object side surface with a smaller radius of curvature than the image side surface, and an object A negative lens with a surface having a smaller radius of curvature than the side surface, an aperture, a negative lens having a surface with a smaller radius of curvature than the image side, an image surface having an absolute radius of curvature than the object side The macro lens according to claim 1, further comprising a positive lens having a surface with a small value.

    [6] The macro lens according to any one of claims 1 to 5, wherein the second lens group includes a cemented positive lens in which a positive lens and a negative lens are cemented.

    [7] In order from the object side, a first lens unit having a positive power, a second lens group having a negative power, and a third lens group having a positive power. The first lens group has a negative meniscus lens having a concave surface on the object side most. A macro lens that is arranged on the object side and moves to the object side independently by changing the interval of each lens group during focusing from the object point at infinity to the closest object point.

    [8] The macro lens according to [7], wherein a stop is disposed in the second lens group.

    [9] The macro lens according to claim 8, wherein the first lens group includes a plurality of positive lenses on the image side of the negative meniscus lens.

    [10] The macro lens according to claim 8 or 9, wherein the lens immediately before and after the stop is a negative lens.

    [11] In the composite lens system of the positive first lens group and the negative second lens group, in order from the object side, a negative meniscus lens having a concave surface on the object side, a positive lens group, and an object side surface having a curvature more than the image side surface A positive lens with a surface with a small radius of curvature, a negative lens with a surface with a smaller radius of curvature than the object side, and a negative lens with a diaphragm, a surface with a smaller radius of curvature on the object side than the image side 9. The macro lens according to claim 7, further comprising a positive lens having a surface whose image side surface has a smaller absolute value of the radius of curvature than the object side surface.

    [12] The macro lens according to any one of claims 7 to 11, wherein the third lens group includes a cemented positive lens in which a positive lens and a negative lens are cemented.

    [13] The macro lens according to any one of claims 1 to 6, wherein the following conditions (3-1) and (4-1) are satisfied.

0.5 <f ₁ / f _L <1.8 (3-1)
1.8 <f ₂ / f _L <3.5 (4-1)
Here, f ₁ is the focal length of the first lens group, f ₂ is the focal length of the second lens group, and f _L is the focal length of the entire system when focusing on an object point at infinity.

    [14] The macro lens as set forth in any one of [7] to [12], wherein the following conditions (3-2) and (4-2) are satisfied.

0.5 <f ₁ / f _L <1.8 (3-2)
1.8 <f ₃ / f _L <3.5 (4-2)
Here, f ₁ is the focal length of the first lens group, f ₃ is the focal length of the third lens group, and f _L is the focal length of the entire system when focusing on an object point at infinity.

    [15] The macro lens according to any one of claims 1 to 14, wherein the following condition (1) is satisfied.

-4 <f _F / f _L <-1 (1)
Here, f _F is the focal length of the negative meniscus lens closest to the object side, and f _L is the focal length of the entire system when focusing on an object point at infinity.

    [16] The macro lens according to any one of [1] to [15], wherein the following condition (2) is satisfied.

−12.5 <(r ₁ + r ₂ ) / (r ₁ −r ₂ ) <− 0.85 (2)
Here, r ₁ is the radius of curvature of the object side surface of the negative meniscus lens closest to the object side, and r ₂ is the radius of curvature of the image side surface of the negative meniscus lens closest to the object side.

    [17] The macro lens according to any one of [1] to [16], wherein the following condition (5) is satisfied at the time of focusing on the closest object point.

-1.0 <MG <-0.4 (5)
However, MG is the maximum photographing magnification.

    [18] The macro lens according to any one of claims 1 to 17, wherein the following condition (7) is satisfied.

1.0 <F <3.0 (7)
However, F is an F number at the time of focusing on an object point at infinity and when the aperture is opened.

    [19] The macro lens according to any one of [1] to [18], wherein the following condition (8) is satisfied.

0.4 <Δd ₁ / f _L <0.8 (8)
However, Δd ₁ is the amount of extension of the first lens group from the time of focusing on an object point at infinity to the time of focusing on the closest object point, and f _L is the focal length of the entire system when focusing on an object point at infinity.

    [20] A camera comprising: the zoom lens according to any one of [1] to [19]; and a mechanism for limiting an imaging range arranged on an image side thereof.

    [21] The camera according to [20], wherein the following condition (6) is satisfied.

7 ° <SW <16 ° (6)
However, SW is an incident half field angle of a diagonal ray incident on the maximum image height in the imaging range of the camera body at the time of focusing on infinity, and the range that can be taken when the imaging range of the imaging surface can be arbitrarily changed Is the maximum value.

    [22] The camera according to claim 20 or 21, wherein the mechanism for limiting the imaging range is a field stop including a rectangular opening.

    [23] The camera according to claim 20 or 21, wherein the mechanism for limiting the imaging range is an electronic imaging device having a rectangular imaging area.

    [24] The macro lens according to any one of [1] to [19], further comprising a camera body formed so as to satisfy the following condition (6) and a mount portion that is detachable.

7 ° <SW <16 ° (6)
However, SW is an incident half field angle of a diagonal ray incident on the maximum image height in the imaging range of the camera body at the time of focusing on infinity, and the range that can be taken when the imaging range of the imaging surface can be arbitrarily changed Is the maximum value.

    [25] The macro lens according to any one of [1] to [19], wherein the following conditions (9) and (10) are satisfied.

13 mm>IH> 10 mm (9)
3.5> f _b / IH (10)
Here, IH is the image circle radius when focusing on an object point at infinity, and f _b is the back focus of the lens system when focusing on an object point at infinity.

    [26] The camera according to claim 23, wherein the following condition (11) is satisfied.

1 ° <| EW | <11 ° (11)
However, EW is the angle formed by the light beam emitted from the diagonal principal ray incident on the maximum image height on the imaging surface of the camera body when focusing on an object point at infinity, and the imaging range on the imaging surface can be changed arbitrarily. If possible, it is the value at the maximum image height within the possible range.

  As is apparent from the above description, according to the present invention, it is possible to provide a macro lens having an F number of 1.8 and a large aperture, and various aberrations corrected favorably from infinity to a short distance.

FIG. 2 is a lens cross-sectional view of the macro lens of Example 1 of the present invention when focusing on an object point at infinity and a magnification of −0.52. It is a lens sectional view similar to FIG. 1 of the macro lens of Example 2 of the present invention. It is a lens sectional view similar to FIG. 1 of the macro lens of Example 3 of the present invention. FIG. 6 is an aberration diagram of Example 1 when focusing at infinity and a magnification of −0.52. FIG. 6 is an aberration diagram similar to FIG. 4 of Example 2. FIG. 6 is an aberration diagram similar to FIG. 4 of Example 3. It is a figure which shows schematic structure of the silver salt type single-lens reflex camera which uses the macro lens of this invention as an imaging lens. It is a conceptual diagram which shows the structure of the digital type single-lens reflex camera incorporating the macro lens of this invention.

Explanation of symbols

G1 ... first lens group G2 ... second lens group G3 ... third lens group S ... stop I ... image plane E ... observer eyeball (eye point)
F ... member 2 such as optical filter ... photographing lens 3 ... optical path 4 ... mount portion 6 ... film 10 ... single lens reflex camera 11 ... quick return mirror 12 ... finder screen 13 ... penta prism 14 ... finder 21 ... objective optical system 22 ... Half mirror prism 23 ... CCD
24 ... Screen mat 25 ... Flat mirror 75
26 ... Relay optical system 27 ... Eyepiece 28 ... Concave mirror prism

Claims (16)

In order from the object side, a first lens group having positive power, a second lens unit having a negative power, a third lens group of positive power, said first lens group, the most object side negative meniscus lens the object-side concave surface of the At the time of focusing from the object point at infinity to the closest object point, the distance between the lens groups is changed and moved to the object side independently, and the following conditions (3-2), (4-2) ), (2), and (8).
0.5 <f ₁ / f _L <1.8 (3-2)
1.8 <f ₃ / f _L <3.5 (4-2)
−12.5 <(r ₁ + r ₂ ) / (r ₁ −r ₂ ) <− 0.85 (2)
0.4 <Δd ₁ / f _L <0.8 (8)
Where f ₁ is the focal length of the first lens unit, f ₃ is the focal length of the third lens unit, f _L is the focal length of the entire system when focusing on an object point at infinity, and r ₁ is the negative meniscus on the most object side. The object side radius of curvature of the lens, r ₂ is the radius of curvature of the image side of the negative meniscus lens closest to the object side, and Δd ₁ is the amount of extension of the first lens unit when focusing on the object point at infinity to focusing on the closest object point. is there. 2. The macro lens according to claim 1, wherein a stop is disposed in the second lens group. The macro lens according to claim 2, wherein the first lens group includes a plurality of positive lenses on the image side of the negative meniscus lens. 4. The macro lens according to claim 2, wherein the lens immediately before and after the stop is a negative lens. The composite lens system of the positive first lens group and the negative second lens group is configured such that, in order from the object side, a negative meniscus lens having a concave surface on the object side, a positive lens group, and an object side having an absolute radius of curvature rather than an image side. Positive lens with a small value surface, negative lens with an image side surface having a smaller radius of curvature than the object side surface, stop, negative lens with an object side surface having a smaller radius of curvature than the image side surface, object side surface 3. The macro lens according to claim 1, further comprising: a positive lens having a surface whose image side surface has a smaller absolute value of the radius of curvature. The macro lens according to any one of claims 1 to 5, wherein the third lens group includes a cemented positive lens in which a positive lens and a negative lens are cemented. The macro lens according to any one of claims 1 to 6, wherein the following condition (1) is satisfied.
-4 <f _F / f _L <-1 (1)
Here, f _F is the focal length of the negative meniscus lens closest to the object side, and f _L is the focal length of the entire system when focusing on an object point at infinity. The macro lens according to claim 1, wherein the following condition (5) is satisfied when the closest object point is focused.
-1.0 <MG <-0.4 (5)
However, MG is the maximum photographing magnification. The macro lens according to any one of claims 1 to 8, wherein the following condition (7) is satisfied.
1.0 <F <3.0 (7)
However, F is an F number at the time of focusing on an object point at infinity and when the aperture is opened. 10. A camera comprising: the zoom lens according to claim 1; and a mechanism for limiting an imaging range arranged on the image side. The camera according to claim 10, wherein the following condition (6) is satisfied.
7 ° <SW <16 ° (6)
However, SW is an incident half field angle of a diagonal ray incident on the maximum image height in the imaging range of the camera body at the time of focusing on infinity, and the range that can be taken when the imaging range of the imaging surface can be arbitrarily changed Is the maximum value. 12. The camera according to claim 10, wherein the mechanism for limiting the imaging range is a field stop including a rectangular aperture. 12. The camera according to claim 10, wherein the mechanism for limiting the imaging range is an electronic imaging device having a rectangular imaging area. 10. The macro lens according to claim 1, further comprising: a camera body formed so as to satisfy the following condition (6);
7 ° <SW <16 ° (6)
However, SW is an incident half field angle of a diagonal ray incident on the maximum image height in the imaging range of the camera body at the time of focusing on infinity, and the range that can be taken when the imaging range of the imaging surface can be arbitrarily changed Is the maximum value. The macro lens according to claim 1, wherein the following conditions (9) and (10) are satisfied.
13 mm>IH> 10 mm (9)
3.5> f _b / IH (10)
Here, IH is the image circle radius when focusing on an object point at infinity, and f _b is the back focus of the lens system when focusing on an object point at infinity. The camera according to claim 13, wherein the following condition (11) is satisfied.
1 ° <| EW | <11 ° (11)
However, EW is the angle formed by the light beam emitted from the diagonal principal ray incident on the maximum image height on the imaging surface of the camera body when focusing on an object point at infinity, and the imaging range on the imaging surface can be changed arbitrarily. If possible, it is the value at the maximum image height within the possible range.

Images