JP3523961B2 - Reverse telephoto wide-angle lens - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inverted telephoto wide-angle lens having a long back focus and being optimal for a single-lens reflex camera. 2. Description of the Related Art Conventionally, a wide-angle lens for a single-lens reflex camera, which requires a long back focus, has a negative lens unit on the front side from the object side and a positive lens unit on the rear side. Inverse telephoto wide-angle lenses configured to be behind the camera have been used. By arranging a strong negative lens on the front side, this type of reverse telephoto wide-angle lens can shoot up to a large angle of view and can increase the amount of peripheral light. [0003] However, in such a conventional reverse telephoto wide-angle lens, in order to enlarge the angle of view while maintaining a long back focus,
The negative refractive power on the front side must be increased, and the asymmetry of the lens configuration increases, and the number of lens components increases in order to correct various aberrations caused by the asymmetry. As a result, the size and cost of the lens must be increased, and ghosts that are harmful to shooting have been caused. Further, there is another problem that when the distortion is corrected by the aberration of the angle of view, the chromatic aberration of magnification is excessively corrected due to the influence. The present invention has been made in view of the above points, and an object of the present invention is to provide an inverted telephoto wide-angle lens having a simple configuration and good imaging performance at a low cost. In order to achieve the above object, the present invention comprises, in order from the object side, a first group of a diverging system, a second group of a converging system, and a third group of a converging system. , The second group and the third
An inverse telephoto wide-angle lens having a stop disposed between the first lens unit and the negative lens unit. The first unit includes at least one negative meniscus lens having a convex surface facing the object side, and the second unit includes a biconvex lens and a negative meniscus lens. The third unit includes a first positive lens having a convex surface facing the image side, a biconcave second lens, a third lens having a positive meniscus having a convex surface facing the image side, and a lens having a weak curvature on the image side. The first lens unit has a low-refractive-index, low-dispersion glass, and the third lens unit has a third lens.
It is an object of the present invention to provide an inverse telephoto wide-angle lens which uses glass of low refractive index, low dispersion and anomalous dispersion for one of the fourth lenses and satisfies the following conditions as a whole. (1) 1.48 <Na <1.52 (2) 59. <Νa <72. (3) 1.48 <Nc5 or Nc7 <1.52 (4) 67 <νc5 or νc7 <85 (5) 0.02 <dc2 / f <0.07 (6) 0.045 <dc4 / f <0 0.065 (7) 1.15 <rc2 / rc3 <1.55 (8) −0.95 <rc4 / rc5 <−0.47 where f: focal length of the entire system Na: refraction of the lens of the first group Nc5, Nc7: Refractive index va of the third or fourth lens of the third group: Abbe number vc5, vc7 of the first group lens: Abbe number dc1, dc2 of the third or fourth lens of the third group: No. On-axis intervals rc1 and rc2 of the respective refracting surfaces sequentially from the object side of the third group: The radius of curvature of each refracting surface sequentially from the object side of the third group. Embodiments and examples of the present invention will be specifically described below with reference to the drawings. In the reverse telephoto wide-angle lens according to the present invention, negative distortion occurs as a characteristic of the reverse telephoto lens. To correct this, a negative refractive power can be corrected to some extent by adding a positive refractive power in the front divergence system or a negative refractive power in the rear convergence system. . However, the correction effect appears in the behavior of the chromatic aberration of magnification with respect to the angle of view, and the short-wavelength light beam is excessively corrected and shakes greatly positively at the maximum angle of view. The difference between the wavelength and the long wavelength opens. In the embodiment of the present invention, chromatic aberration of magnification is appropriately generated in the diverging system on the front side, and anomalous dispersion glass is used for the positive refractive power in the converging system on the rear side. Further, the chromatic aberration of magnification at which the short-wavelength light beam is overcorrected at the maximum angle of view is corrected. The above-mentioned conditional expressions (1) to (4) define the specifications of the glass used in this embodiment. If the glass is out of the conditions, the above-mentioned chromatic aberration of magnification occurs. If the lens is forcibly corrected, the load on the glass of the cemented lens of the biconvex lens of the second group B and the negative meniscus lens will not only be reduced, but also axial chromatic aberration and distortion will not be properly corrected. Increases, and a negative deviation of astigmatism occurs. On the other hand, conditional expressions (5) and (7) satisfy the third group C
This defines the shape of the air lens sandwiched between the first lens and the second lens. If the condition is not satisfied, high-order spherical aberration occurs at the outermost periphery of the air lens, and the on-axis and off-axis aberrations occur. Cannot be balanced, and a uniform image cannot be obtained from the center of the screen to the maximum angle of view. Further, conditional expressions (6) and (8) satisfy the third condition.
This defines the shape of the air lens interposed between the second lens and the third lens of the group C. If the air lens deviates from this condition, coma aberration occurs off-axis due to the influence of higher-order aberrations, and condensing is asymmetric. , And the image appears to flow due to the fluctuation of the image plane.
It is also possible to remove the flare component by providing a shielding plate or the like in the middle of the lens, but this is not preferable because the amount of peripheral light decreases. In particular, the chromatic aberration of magnification is deteriorated particularly for short-wavelength light rays, and color bleeding occurs. [Embodiments] Next, embodiments of the reverse telephoto wide-angle lens according to the present invention will be described. Note that FIGS. 1 to 4
FIG. 3 is a diagram illustrating a configuration of each of Embodiments 1 to 4, wherein the aperture ratio is F / 2.8 and the angle of view is 2ω = 64 °. Example 1 f = 1.0 ω = 32. (Deg) fb / f = 1.08 Radius of curvature Surface spacing Abbe number Refractive index rA1 = 2.1634708 dA1 = 0.0448998 νA1 = 64.15 nA1 = 1.516330 rA2 = 0.3769795 dB0 = 0.3353951 rB1 = 0.7602857 dB1 = 0.1789976 νB1 = 53.84 nB1 = 1.712995 rB2 = -0.4402586 dB2 = 0.0539197 νB2 = 47.09 nB2 = 1.623740 rB3 = -2.1108777 dB3 = 0.1140571 ∞ dC0 = 0.0914290 rC1 = -68.1514508 dC1 = 0.1224984 νC1 = 42. dC2 = 0.0266693 rC3 = -0.5068733 dC3 = 0.0396166 νC3 = 31.71 nC3 = 1.739997 rC4 = 1.1052598 dC4 = 0.0609059 rC5 = -1.3334206 dC5 = 0.0648628 νC5 = 81.61 nC5 = 1.496999 rC6 = -0.5131841 dC6 = 0.00138891 dC6 = 0.00138891 = 52.65 nC7 = 1.740999 rC8 = -1.0858001 Example 2 f = 1.0 ω = 32. (Deg) fb / f = 1.16 Radius of curvature Surface spacing Abbe number Refractive index rA1 = 0.5663532 dA1 = 0.0445713 νA1 = 64.15 nA1 = 1.516330 rA2 = 0.3388079 dA2 = 0.1226215 rA3 = 1.0748461 dA3 = 0.0531473 νA3 = 70.21 nA3 = 1.487490 rA4 = 0.5372219 dB0 = 0.2508066 rB1 = 0.9526398 dB1 = 0.1593622 ν B1 = 44.76 nB1 = 1.788423 rB2 = -0.4179881 dB2 = 0.0806019 νB2 = 37.67 nB2 = 1.645753 rB3 = -4.6668740 dB3 = 0.1035940 ∞ dC0 = 0.0733867 rC1 = -1.6579585 dC1 = 0.0575774 νC1 = 44.18 rC2 = 1.785 nC1 = 2 rC3 = -0.4966085 dC3 = 0.0379582 νC3 = 33.80 nC3 = 1.647689 rC4 = 1.1712612 dC4 = 0.0489132 rC5 = -2.2253443 dC5 = 0.0714946 νC5 = 81.61 nC5 = 1.496999 rC6 = -0.5491876 dC6 = 0.0037879 rC7 = 69697C7 = 6 = 1.517277 rC8 = -0.8161497 Example 3 f = 1.0 ω = 32. (Deg) fb / f = 1.20 Curvature radius Surface spacing Abbe number Refractive index rA1 = 0.7583134 dA1 = 0.0528516 νA1 = 64.15 nA1 = 1.516330 rA2 = 0.3551229 dA2 = 0.0997792 rA3 = 0.7482024 dA3 = 0.0394297 νA3 = 70.21 nA3 = 1.487490 rA4 = 0.4683223 dB0 = 0.2186583 rB1 = 0.9483278 dB1 = 0.1595346 νB1 = 40.10 nB1 = 1.762001 rB2 = -0.4137513 dB2 = 0.133887310B2 = 32 dB3 = 0.0634589 ∞ dC0 = 0.0547690 rC1 = -1.4678210 dC1 = 0.0620445 νC1 = 47.38 nC1 = 1.788001 rC2 = -0.6221953 dC2 = 0.0619118 rC3 = -0.5206323 dC3 = 0.0656718 vC3 = 33.80 nC3 = 1.647689 rC4 = 1.1717876 dC4 = 0.0544318 rC5 = -1.5187131 dC5 = 0.0677920 νC5 = 81.61 nC5 = 1.496999 rC6 = -0.5182080 dC6 = 0.0037988 rC7 = 29.0356720 dC7 = 0.0 Example 4 f = 1.0 ω = 32. (Deg) fb / f = 1.20 Radius of curvature Surface spacing Abbe number Refractive index rA1 = 0.8036827 dA1 = 0.0542846 νA1 = 64.15 nA1 = 1.516330 rA2 = 0.3628432 dA2 = 0.1128176 rA3 = 0.7382524 dA3 = 0.0447252 νA3 = 70.21 nA3 = 1.487490 rA4 = 0.4927830 dB0 = 0.2376727 rB1 = 0.9656855 dB1 = 0.1376794 νB1 = 40.10 nB1 = 1.762001 rB2 = -0.4217434 dB2 = 0.1577267 νB2 = 32.700 nB3 = 1.672 933 ∞ dC0 = 0.0550989 rC1 = -1.3562523 dC1 = 0.0443761 νC1 = 47.38 nC1 = 1.788001 rC2 = -0.6369777 dC2 = 0.0671148 rC3 = -0.5140368 dC3 = 0.0824129 νC3 = 33.80 nC3 = 1.647689 rC4 = 1.2057899dC4 = 1.20578991.36 νC5 = 81.61 nC5 = 1.496999 rC6 = -0.5247903 dC6 = 0.0028128 rC7 = 6.7360978 dC7 = 0.0612980 νC7 = 81.61 nC7 = 1.4969 Where rA1, rA2 ... are the radii of curvature of the respective surfaces of the lenses, dA1, dA2 ... are the thicknesses and air gaps of the lenses, νA1, νA3 are the Abbe numbers of the lenses,
.. are the refractive indexes of the lenses. FIGS. 5 to 8 show Embodiments 1 to 4, respectively.
FIG. 9 to FIG. 12 are diagrams showing the lateral aberration correction situations of Examples 1 to 4, respectively.
3 (a), (b), (c), and (d) are diagrams illustrating magnification chromatic aberration correction states of Examples 1 to 4, respectively. As is apparent from the aberration correction situations shown in the above-described diagrams, each of the above-described embodiments 1 to 4 has a wide angle of view, a long back focus, and a bright aperture ratio. It can be seen that various aberrations are well corrected. As described above, the inverted telephoto wide-angle lens according to the present invention has a low refractive index and low dispersion glass in the first lens group and a third and fourth glass in the third lens group. Low refractive index, low dispersion and anomalous dispersion glass are used for either of the positive lenses, so that the back focus is long, the angle of view is wide, and the aperture ratio is bright. It becomes possible to satisfactorily correct lateral chromatic aberration that has been excessively corrected with the correction. When the reverse telephoto wide-angle lens according to the present invention is used as a wide-angle lens for a single-lens reflex camera, the effective diameter of the first group of lens elements is relatively small despite the reverse telephoto type. Therefore, it is convenient to use a common filter screw diameter with various types of interchangeable lenses including a standard lens.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a configuration diagram of a first embodiment of the present invention. FIG. 2 is a configuration diagram of a second embodiment of the present invention. FIG. 3 is a configuration diagram of a third embodiment of the present invention. FIG. 4 is a configuration diagram of a fourth embodiment of the present invention. FIG. 5 is a diagram showing a longitudinal aberration correction situation according to the first embodiment. FIG. 6 is a diagram illustrating a longitudinal aberration correction situation according to a second embodiment. FIG. 7 is a diagram showing a longitudinal aberration correction situation according to a third embodiment. FIG. 8 is a diagram showing a longitudinal aberration correction situation according to a fourth embodiment. FIG. 9 is a diagram showing a lateral aberration correction situation in the first embodiment. FIG. 10 is a diagram illustrating a lateral aberration correction situation according to the second embodiment. FIG. 11 is a diagram illustrating a lateral aberration correction situation according to a third embodiment. FIG. 12 is a diagram showing a lateral aberration correction situation according to a fourth embodiment. FIG. 13 is a diagram showing a magnification chromatic aberration correction situation of each embodiment. [Description of Signs] rAi (i = 1 to 4): radius of curvature of the i-th surface from the object side of the first group rBi (i = 1 to 3): curvature of the i-th surface from the object side of the second group Radius rCi (i = 1 to 8): radius of curvature dAi (i = 1 to 3) of the i-th surface from the object side of the third group: i-th and i from the object side of the first group
The surface distance dBi (i = 0 to 3) from the (+1) th: i-th and i from the object side of the second lens unit
The surface distance dCi (i = 0 to 7) from the (+1) th: i-th and i from the object side of the third lens unit
Surface distance from + 1st: SA: spherical aberration AS: astigmatism DIST: distortion 2ω: angle of view S: stop TC: chromatic aberration of magnification

Claims (1)

(57) [Claims 1] A first group of a diverging system, a second group of a converging system, and a third group of a converging system are arranged in this order from the object side.
An inverse telephoto wide-angle lens having a stop disposed between the first lens unit and the second lens unit. The first unit includes at least one negative meniscus lens having a convex surface facing the object side, and the second unit includes a biconvex lens and a negative meniscus lens. The third unit includes a first positive lens having a convex surface facing the image side, a biconcave second lens, a third lens having a positive meniscus having a convex surface facing the image side, and a lens having a weak curvature on the image side. The first lens group includes a low refractive index and low dispersion glass, and the third lens group includes a third lens and a fourth lens.
An inverse telephoto wide-angle lens which uses low refractive index, low dispersion and anomalous dispersion glass for one of the lenses and satisfies the following conditions as a whole. (1) 1.48 <Na <1.52 (2) 59. <Νa <72. (3) 1.48 <Nc5 or Nc7 <1.52 (4) 67 <νc5 or νc7 <85 (5) 0.02 <dc2 / f <0.07 (6) 0.045 <dc4 / f <0 0.065 (7) 1.15 <rc2 / rc3 <1.55 (8) −0.95 <rc4 / rc5 <−0.47 where f: focal length of the entire system Na: refraction of the lens of the first group Nc5, Nc7: Refractive index va of the third or fourth lens of the third group: Abbe number vc5, vc7 of the first group lens: Abbe number dc1, dc2 of the third or fourth lens of the third group: No. On-axis intervals rc1 and rc2 of the respective refracting surfaces sequentially from the object side of the third group: The radius of curvature of each refracting surface sequentially from the object side of the third group.