JPS5822724B2 - Hikiyuumen O Mochiita Daikokeikouka Cleanse - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a large-diameter wide-angle lens, and particularly to a lens having an aspherical surface.

A wide-angle lens for a single-lens reflex camera is a reverse telephoto lens in which a lens group with negative refractive power is placed in front of a lens group with positive refractive power in order to obtain a long back focus that does not impede the movement of the movable reflector. It is common to use type.

In this type of lens, the rear group requires strong positive refractive power in order to converge the light beam that diverges in the front group, so there are many difficulties in obtaining a large-diameter lens.

As a large aperture lens, the spherical aberration is small and does not become over-corrected, the meridian and spherical image planes are flat, the chromatic aberration is well corrected, and especially the flare of the spherical beam is small. This is because wide-angle lenses are required to have small distortion aberrations, but these requirements conflict with miniaturization of lenses.

In other words, the larger the distance between the front and rear lens groups, the easier it is to obtain a long back focus, but in order to cover a wide angle of view, the effective diameter of the front negative refractive power lens group must be increased, which increases the volumetric weight. This makes operation inconvenient.

In addition, the distance between the front and rear lens groups has been reduced, making the overall size smaller.
Moreover, in order to obtain a long back focus, it is necessary to strengthen the co-refractive power of the front and rear lens groups, which increases the coma, distortion, and chromatic aberration of magnification that occur in the front lens group, making it difficult to correct them. The generated spherical aberration increases, and if this spherical aberration is corrected, the flare of the spherical beam will increase.

The present invention solves the above problems and provides brightness Fl, 2 angles of view 62
The objective is to obtain a large-diameter wide-angle lens that is small in size and has a small aperture diameter, has a long backfocus equal to or longer than the focal length, and is composed entirely of three lens groups. 1st
The group consists of a meniscus negative lens with the convex side facing the object, a positive lens, and a biconcave negative lens, and the lens group as a whole has negative refractive power.The first group consists of a biconvex positive lens, a positive lens, and a negative lens in order. It consists of a laminated lens, and the lens group has a positive refractive power as a whole.The first group is a negative lens with a strong diverging surface facing the object side, followed by two or more positive lenses or a laminated positive lens. This is achieved by placing one or more positive lenses or positive laminated lenses after a laminated lens consisting of a negative lens with a strong diverging surface facing the object side, or a positive laminated lens, thereby arranging a lens group with a positive refractive power as a whole. ing.

The reverse telephoto wide-angle lens according to the present invention has two negative lenses in the front diverging first group to reduce the share of aberrations of each lens, and a positive lens is placed between the two diverging lenses. This makes it possible to minimize distortion and chromatic aberration of magnification occurring in the fourth lens group and give the first group strong refractive power. By having the convergence effect shared by the surface, the occurrence of spherical aberration can be minimized.The second surface of the second lens has the effect of correcting the coma aberration that occurs in the first lens group, and the second lens is made of a low-dispersion glass third lens. By laminating these lenses with high-dispersion glass, we can correct axial chromatic aberration, give the lens a strong convergence effect as a whole, and make it possible to reduce the aperture diameter.
The rear converging second lens group uses high-dispersion glass to provide a strong diverging surface to correct the chromatic aberration of magnification that occurs in the first lens group.

Then, the spherical aberration and astigmatism that occur on the second surface of the second lens in the second group, which is the surface that corrects coma aberration, are corrected, and the convex surface facing the image plane of the converging lens that follows it is made an aspherical surface. This allows excellent correction of spherical aberration, coma, astigmatism, and distortion.

It is.

The numerical ranges in which even better images can be obtained with the above-mentioned configuration are shown below.

Place the aperture between the 1st group and the
Distance L■ from the front principal point of system ■; Thickness FB of the ■th group; Focal length RB of the first group; Radius of curvature R of the strongest diverging surface of the first group ■;
Radius of curvature f of the most strongly divergent surface of the group: When taken as the focal length of the entire system, ■ 1. ．． 7'<DI, IV<1.8 f■ 0.9
f < FB < 12f ■ 0.46f < L ■ < 0.64f ■ 1.5 < RB /R ■ < 2.5, and in addition, 12 is an aspheric surface, the paraxial radius of curvature Ri at the apex of the aspheric surface, the X axis is on the optical axis, the Y axis is perpendicular to it, and the aspheric surface is expressed as: This satisfies each condition when the refractive index is N1.

In such a configuration, the second condition indicates the range in which the entire lens can be miniaturized and aberration correction is good.If the upper limit is exceeded, the overall length of the lens becomes large and the effective diameter of the front lens becomes large. As the entire lens becomes larger and exceeds its lower limit, the refractive power of the first group, first group, and second group becomes stronger, so even if it has an aspherical surface, it will not be possible to correct each aberration well. .

The second condition indicates the range for minimizing the occurrence of spherical aberration and keeping the aperture diameter small.If the upper limit is exceeded, the aperture diameter increases, which is undesirable for the lens barrel mechanism. If the value exceeds 1, the spherical aberration increases and becomes difficult to correct even with an aspherical surface.

The third condition indicates the range in which the effective diameter of the rear lens can be kept small and the refractive power required for the second group can be obtained while maintaining good aberration correction.If the upper limit is exceeded, the diameter of the rear lens will increase. If the lower limit value is exceeded, it becomes impossible to provide the diverging surface necessary for correcting spherical aberration in order to obtain the necessary refractive power for the second group.

The fourth condition indicates the range in which spherical aberration and astigmatism on the diverging surfaces of the first and second groups are well corrected.If the upper limit is exceeded, astigmatism is corrected. If it becomes excessive and exceeds the lower limit, it becomes difficult to correct spherical aberration.

Since aspherical surfaces are significantly more difficult to process than spherical surfaces and are more expensive to process, it is required to obtain the maximum effect with the minimum number of surfaces and the minimum amount of aspherical surfaces.

In lens systems with large pupil aberrations, such as reverse telephoto wide-angle lenses, using an aspherical surface on the convex surface behind the aperture can reduce spherical aberration,
It is most effective for correcting coma, astigmatism, and distortion aberrations and for reducing flare of spherical beams.The fifth condition indicates the optimum range of the aspheric surface, and if the upper limit is exceeded, If the coma aberration and astigmatism at intermediate angles of view become overcorrected and exceed the lower limit, the correction of spherical aberration in the middle of the beam and coma aberration at intermediate angles of view will become insufficient, and in addition, flare of the spherical beam at high angles of view will occur. increases.

In order to maintain good flatness of the image plane up to a high angle of view in a lens system that satisfies the above configuration and conditional expression, it is necessary to bring the Petzval sum close to O. Good results can be obtained by setting the average refractive index of the positive lens to 1.7 or more, and this is also effective in suppressing the occurrence of spherical aberration.

Furthermore, when shooting at close range, as is well known, by reducing the distance between the second lens of the first group and the third lens, it is possible to reduce fluctuations in astigmatism. It is possible to reduce fluctuations in b-coma aberration, which increases the distance between the lens and its front lens.

The present invention will be explained in detail below.

Example 1 (Figures 1, 2A to 2D) F=1.22 2ω=64° 15-sided valve spherical surface Aspheric coefficient A=0, B=1.05836×10-”.

C=1.05001×10-8. D=1.828
5X10-"E=-3,48X 10-13 Focal length=35.24, Back focus-36, 5th ■ group rear principal point - 5th ■group Combined system front principal point DI, ■=4
2.82 Focal length of the first group Fl - 37.62 Thickness of the ■ group Llll - 20,37 Where, r is the radius of curvature of the lens, d is the axial lens thickness or lens surface spacing, N is the refractive index, ν is variance.

The various aberration coefficients of Example 1 are the longitudinal chromatic aberration coefficient, T is the lateral chromatic aberration coefficient, SA is the spherical aberration coefficient, CM is the comatic aberration coefficient, As is the astigmatism coefficient,
PT is the Petzval sum, and DS is the distortion coefficient.

Example 2 (Figures 3, 4A to 4D) F=1.2 2ω=64° Various aberration coefficients of Example 2 15-face valve spherical surface A=0, B=5.6788X 10-6C=- 9,
501LX 10 inches 11 D=9.6321XIO
-”E=-1,7238X 10-” Focal length=35.5 Back focus -36.5
DI, ■=47.32 Fl]=36.92 L]'[=19.22'Example 3 (Fig. 5, Fig. 6A to Fig. 6D) 14-sided valve spherical surface A=0, B=6. 217X10-6. C2 1.965
3X10-9°D near, 6209X10-12 E=-
1,845X10-14 focal length -35.5, back focus -36.5DI, ■=47.96 FIl236.4.1 Ll'[=19.89 Various aberration coefficients of Example 3 Example 4 (No. 7, 8A to 8D) F=1.2 2ω=64° 15-sided valve spherical surface A=O, B=4.271X10-6. c=3.5o12
x1o-9°D=4.7495X10-12. E=-1
, 1376E-14 focal length = 355, back focus -36.5DB, 1y = 57.6 F = 37.9 Lll = 17.81 Various aberration coefficients of Example 4

[Brief explanation of the drawing]

FIG. 1 shows an example of the lens of the present invention, and FIGS. 2A to 2D are diagrams of various aberrations of Example 1. FIG. 3 shows another example of the lens, and FIGS. 4A to 4D are diagrams of various aberrations of Example 2. FIG. 5 shows another lens example, and FIGS. 68 to 6D are various aberration diagrams of Example 3. FIG. 7 shows another example of the lens, and FIGS. 8A to 8D are diagrams of various aberrations of Example 4. In the figure, r is the radius of curvature of the lens, and d is the axial lens thickness or lens surface spacing.

Claims (1)

[Claims] 1. In order from the subject side, a negative meniscus lens, a positive lens, a negative first group including a negative lens, a biconvex positive lens,
A first lens unit that is entirely positive, which has a laminated lens consisting of a positive lens and a negative lens, a negative lens with a diverging surface that is strong against the subject, and behind it, three positive lenses or two lenses that include a laminated positive lens. It consists of a positive lens group, which is a combination of a negative lens and a positive lens with a positive lens or a strong diverging surface facing the subject, and two positive lenses behind it. At least one of the convex surfaces facing the image side of is aspherical, DI, rv is the distance between the rear principal point of the first group and the front principal point of the synthetic yarn ■ of the first group and the group ■, L■ is the thickness of the ■ group, 1'''It is the focal length of the first group, RH is the radius of curvature of the strongest diverging surface of the first group, R■ is II
When the radius of curvature of the most strongly diverging surface of the group, f, is the focal length of the gold thread, 1, . 7'<DI,Iy(1,8f O,9f<FB (1,2f O,46f(Llll(0,64f 1.5(RB /RH<2.5) A large-diameter wide-angle lens using a spherical surface.