JPS5821710A - Lens system which permits near distance photographing - Google Patents

Abstract

PURPOSE:To obtain a general-purpose lens system of a large aperture ratio which consists of a front group having positive refracting power and a rear group having likewise positive refracting power, can be focused to all objects from infinite distances up to extreme near distances, and maintains high optical performance at all times. CONSTITUTION:A titled lens system consists of a front group G1 and a rear group G2; the front group G1 is constituted of three lens elements L1, L2, L3 and the rear group G2 is constituted of two lens elements L4, L5, respectively. Since the front and rear groups require the degree of freedom in achromatism, the lenses having negative refracting power are always contained therein. If the combined focal length of the entire system is defined as (f) and the focal lengths of the front and rear groups are defined as f1, f2 respectively, it is preferable to regulate these to 1.6<f1/f<3.0, 1.5<f1/f2<3.0. To focus the lens from infinite distances to a near distance, the entire part thereof is extended to an object side while the air space between the front group G1 and the rear group G2, that is, the air space between the 3rd lens L3 and the 4th lens L4 is expanded, whereby the lens is focused to the extremely near distances down to beta=-0.5 image magnification.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a large aperture ratio general-purpose lens system that can photograph objects at any distance from infinity to extremely close distances.

Conventionally, a dedicated optical system has been required depending on the specific use, even for close-up photography, which is often used. Chikaomi - So-called microlenses or macro lenses, which are lens systems designed for photographic use but are used as general-purpose lenses, as you can see, still have insufficient optical performance in mass-produced Chikaomi. Those with good performance generally had more lenses and tended to have complex optical systems.

The purpose of the present invention is to provide a general-purpose lens system with a large aperture ratio that can focus on any object from infinity to extremely close objects, while maintaining a simple optical system with a small number of lenses, and that always maintains excellent optical performance. Then there is K.

The lens system capable of close-range photography of the present invention includes at least 41 negative lens components and has 1111 positive refracting components.
-01 and a rear group G2, which also has positive refractive power and includes at least -1 negative lens component, and the air gap between the two groups is adjusted to allow focusing from an object at infinity to a close object. At this time, the structure is such that both groups are moved toward the object side while increasing the air gap between the two groups. Moreover, the aperture stop is provided closer to the image side than the lens closest to the object in the rear group.

By setting the aperture in or after the rear group, the exit pupil can be brought closer to the lens. The problem with this is that when connecting another optical system such as a rear conversion lens behind such a lens system, even if the effective diameter of that optical system is small, the luminous flux may be cut off too much (reduction in peripheral light intensity). In addition, by moving the aperture closer to the rear of the lens, it is possible to make the effective diameter of the lens in the rear group relatively small, and the aperture of other optical systems installed behind the rear group can also be made relatively small. It can be made relatively small, which is advantageous in reducing wrinkles in the lens as a whole.

1 In addition, in the present invention, the first group G after 11t1 during close-range photography
Since the air spacing between L and G2 becomes larger, the angle of the incident light beam moving farther from the object and entering the lens system with respect to the optical axis becomes smaller, making it easier to correct aberrations. Also, taking these into account, it is possible to reduce the occurrence of aberrations during close-up photography with a simple lens system by appropriately balancing the distribution of refractive power between the front and rear groups, that is, the distribution of apparent brightness. .

When increasing the aperture ratio of this type of lens system according to the present invention and attempting to obtain a sufficiently long bank focus, the refractive power of the front group tends to be significantly weaker than the refractive power of the rear group. When increasing the aperture ratio, the number of lenses increases, the thickness of the lens becomes noticeably thicker, and the back focus tends to become shorter. Therefore, in order to obtain sufficient back focus when photographing an object at infinity, the refractive power of the front group must be adjusted. This means that the light flux emitted from the object is not converged very much, and the closer the object is to the object, the more the light emitted from the front group will diverge. This light beam is received by the rear group, and it is extremely difficult to configure the rear group to increase its refractive power and brightness or to correct various aberrations well.

For this reason, it is necessary to strengthen the refractive power of the front group compared to conventional large aperture ratio lenses of this type, and to increase the load on the front group as much as possible. In this way, the burden of aberration correction on the rear group is reduced at close range, and even at close range, the light beam emitted from the object can be used as a convergent light beam in the front group. However, if the refractive power of the front group becomes too strong, it becomes difficult to correct aberrations in the front group, so it is necessary to reduce the amount of light from the object at the closest distance so that it becomes a slightly divergent beam and exits the front group. is desirable.

Considering the bone quality of the lens system according to the present invention as described above, it is desirable that the following conditions be satisfied.

1.6(f, /f(3,0...(1)1,5
(f, / f, (3,0... (2) where f is the composite focal length of the entire system - e, and fj + fl represent the focal lengths of the front group and rear group, respectively. In equation (1), The condition stipulates the appropriate distribution of refractive power to the st1 axis.Under this condition, if it exceeds @, the refractive power of the front group becomes too strong and the back focus is insufficient at infinity photography. At the same time, the variation in spherical aberration between the shooting conditions of an object at infinity and the shooting condition of a close-up object becomes significant. On the other hand, if the upper limit is exceeded, the refractive power load on the rear group becomes relatively too strong.
Significant spherical aberration occurs at close range, making correction difficult. Increasing the refractive power of the rear group is effective as mentioned above, but it is disadvantageous for objects at close range, and for a lens system that achieves a high imaging magnification like the one of the present invention, it is necessary to is desirable.

The conditions for equation (2) are the ratio of the focal lengths of the front group and the rear group,
In other words, it determines the distribution of refractive power, and together with the condition of equation (1), it is necessary to obtain a bright and close-range image (and a high photographic magnification).This condition also meets the condition of equation (1). This determines the distance between the front and rear groups.If the lower limit is exceeded, the refractive power of the front group becomes too strong and the wa difference between the front groups increases.To correct this, However, it is possible to increase the number of lenses in the front group and make the lenses thicker.
Since the principal point of the front group goes into the lens, the lenses of both groups will interfere when photographing an object as close as 4 meters to infinity, so it is used as a lens □ and □ for general photography. Things become strange. If the upper limit is exceeded, good aberration correction is possible in infinity shooting conditions even if the brightness is quite high, but in close-up shooting conditions, various aberrations occur significantly and good correction cannot be maintained.゛In such a lens unit of the present invention, the change in the air distance between the front group and the rear group that is expanded by correction is defined as Δd□
, when the amount of change in back focus when focusing on a mass-produced relative from infinity is ΔBf, α=4d/no1t
α is a coefficient that determines the floating amount, but the following is preferable.

o, 2〈α'< 0.35... (3) If the lower limit of equation (3) is exceeded, it is difficult to correct external force tropic coma in close-range photography, and the floating effect I don't have much hope. In addition, when the upper limit of equation (3) is raised, introverted comatic aberration occurs in close-range shooting conditions, and if there is excessive floating, the meridional plane becomes excessively positive, resulting in a negative image. The surface becomes too negative, creating astigmatism, which is undesirable.

Specifically, it is desirable that the front group and rear group constituting the lens system according to #4 of the present invention be constructed as follows. In other words, the front group false is, in order from the object side, the third lens L, which is a positive lens with a surface with a stronger curvature facing the object side, and the second lens L, which is a positive meniscus lens with a convex surface facing the object side. The third lens is a negative meniscus lens with the convex surface facing toward the rear, and the fourth lens is a positive meniscus lens with the convex surface facing the rear. It is desirable that the system be of a so-called modified Gaussian type. However, as mentioned above, the present invention is completely different from the conventional deformed Gauss type lens system in that the aperture pattern is provided between the fourth lens and the fifth lens as described below. [There is.

Furthermore, in this development, even if the front and rear groups are moved significantly, there should not be too much performance deterioration due to chromatic aberration. In order to correct magnification and axial chromatic aberration due to focusing with a relatively simple configuration, K uses the lens L1, which is the older positive lens in the front group, as a low fractional positive lens. It is desirable to configure the lens with high dispersion and the ms lens, which is a negative lens, with high dispersion. When a lens system is made to have a large aperture ratio, the positive lens component generally has a high refractive index to correct spherical aberration, and the negative lens component has a low refractive index to correct non-single point aberration. In the present invention, the Gaussian type lens requires a high refractive index and low dispersion Ml lens, but in practice this rarely exists, so a bonded lens is used. Similarly, since the third lens L does not have much glass with low refractive index and high dispersion, it is inevitably a bonded lens. Specifically, if the average refractive index of each lens is N, then a range of 1.70 (N, (1,82...(4)-) is desirable.

If the upper limit of equation (4) is exceeded, correction of chromatic aberration becomes difficult.

Furthermore, if the lower limit of equation 4 is exceeded, it becomes difficult to correct astigmatism, spherical aberration, and coma aberration.

In such a 5KH lens, it is desirable to have a force of Np)Nn, where NptX is the average refractive index of the positive lens component included in each evaluation, and NIIK is the average NIIK of the negative lens component. This is because if both the average refractive indexes Np and Nn become too low, zonal spherical aberration will occur and the lens will not wear well.
This is because both p and Nu become too high, and the one-sphere image plane becomes excessively negatively curved, which is not desirable.

Examples of the present invention will be described in detail below.

In all of Examples 1 to 4, the focal length @1=100,
It has an r number of 2.5 and is basically a modified Gaussian type consisting of five lens components. As mentioned above, the entire system consists of two groups, the front group G and the rear #false. The front group G has three lens components Ls - and -I4, and the rear group false has two lens components.
Since each IIIPK around 0, which is composed of two lens components - and I4, requires a degree of freedom in achromatization, a lens with negative refractive power is always included. In the embodiment, an aperture is provided between the #I4 lens and the fifth lens.

When focusing from infinity to close range jIIK, the photographing magnification β is increased by increasing the air gap between the front group G and the rear group, that is, the air gap between the 1s3 lens and the 4th lens, and moving the entire lens toward the object side. Focusing is done at extremely short distances, unlike knees 0 and 5.

In the $11% example, the closest distance is R=-4s8J426 a
The maximum magnification is -0.51482, and the aperture is located 0.8 s behind the fourth lens in the rear group. As described above, this embodiment has the simplest structure, consisting of six lenses in total, consisting of four rattan lenses bonded together with negative and positive lenses. The specifications of the side 1 embodiment are shown in the fs1 table, and the lens arrangement is as shown in the irises 1 diagram. The aberration diagrams are shown in Figure 2 for the non-distant shooting condition and in Figure 3 for the closest shooting condition II (β=-0, 52). For each aberration 1, # plane aberration (Spk),
Astigmatism (Ant,).

Distortion aberration (Dis, ), lateral chromatic aberration (LL Chr,
) showed that.

In the second impeachment example, the deceitful and close vassal class is R=4712917 m and the maximum magnification is -0.5. The aperture is located 1.0 mm behind the fourth lens in the middle of the rear group.

This example is an optical system consisting of 7 elements in 5 groups, and in contrast to the v4 example IK, there are 3 lenses L, a positive lens -1 and a negative lens L.
This is made by laminating two lenses together with ll and chromatic aberration, which balances out the achromatism caused by the front #P false image and suppresses fluctuations in chromatic aberration during focusing. Also 1s4 lens-
is composed of a single meniscus lens, and the fifth lens is a negative lens I41 and a positive lens L1 bonded together. The specifications of Example #I2 are as shown in Table 2, and a lens arrangement diagram is shown in FIG. The aberration diagrams are shown in Figure 5 for infinity photography and 1! for closest distance photography! l(β=-0,
5) are shown in FIG.

In the third example, the closest distance is R=4694675 m and the maximum magnification is 10.5. It is located 1.0- behind the #4 lens in the false middle after the aperture.

This embodiment is an optical system consisting of seven lenses in total, and the negative and positive bonding of the third lens in the second embodiment is reversed to form a positive and negative bonding lens. I did it.

The specifications of the third embodiment are as shown in Table 3, and the lens arrangement is shown in FIG. The aberration diagram is Figure 8 at infinity, and Figure 1g9 at close distance #w (, β = -0, 5).

In the fourth embodiment, the closest distance is R=4614913 m and the maximum magnification is -051482. The diaphragm is the fourth in the second generation
It is located 0.8- behind the lens. This embodiment is an optical system consisting of seven lenses in total, and unlike the ts1 embodiment, the first lens is a positive lens and a negative lens L-s-Lq.
* By using a bonded lens, fluctuations in chromatic aberration at zero magnification of axial chromatic aberration during focusing are reduced. The specifications of the fourth embodiment are as shown in Table 4, and the lens arrangement is as shown in Figure 1O. The aberration diagrams are shown in FIG. 11 at infinity and in FIG. 12 at the closest distance Im&(β=-0, 52).

$11゜First example f=100F number: 2.5r*=
27.630 ds=variable r0-287,811d
lI; Variable f, = 258.9802 f, = 100.42 α = Qjj 782 Table 1 Second Example f-100F Number 2 2.5rv=
26347 dv=variable ru=81.616 dl,=variable fl=20
4 f, = 107.6923 α = 0.2811 Table 3゜Third Example f = 100F number = 2.57, ==
27f5834. −Kl variable r,,= −79b0
8 al, -518f, =204 f wealth = 107.6923 α = 0.2811 Table 4゜411th example f = 100F Nan/(-:26rt”
26981 d, = variable f1 = 258.9802 f, -100,4200 α = 0.2782 From the comparison of each aberration diagram, it can be seen that although the lens system according to the present invention has a large aperture ratio of F number 2.5, it is difficult to reach infinity. Of course,
It can be seen that the lens maintains excellent yield performance even at extremely close distances with a photographic magnification/knee of 0.5.

As described above, according to the present invention, it is possible to achieve a general-purpose lens system with a simple construction and an excellent large aperture ratio capable of photographing from infinity to extremely close distances.

[Brief explanation of drawings]

No. i11. Figure 4, Figure 7, and Figure 10 are layout diagrams of the infinite state of each embodiment, respectively, and Figure 2, Figure S, and Figure 8
The figure and FIG. 11 are aberration diagrams in an infinite state, respectively.
FIGS. 3, 6, and 9 and Rattan 12WJ are aberration diagrams of mass-produced models. [Explanation of symbols of main parts] at...front group 0,...to rear group L%,...lens Fig. 2 3rk, Ast. F・2,5 W・12.2°-2,50
2,50-11,lQ O,10 Figure 3 6P ASt DrS Lt, Chr Figure 5 SPh A5t. Fig. 6 δph, 'A5t/ DtS L't/, (Ar. O Fig. 8 3Ph, AS+. Di, S IJ, Chr-250
! bu -uy+u u1uoqFigure 61'h ASt/D;5 Lt/, CFLr. -i, su 7. bLl
-Diυ 01a 11 prisoners δrll A6-b. F=2.5 (t/
=I2. f'Dis lt, CFt
r-13u 2. QU
-0,100,10, ;) t-12 diagram

Claims (1)

[Claims] 1. It consists of a front group having a positive refractive power and a rear group also having a positive refractive power, each group including at least one negative lens component, and an aperture stop. It is more focused than the lens closest to the object in the rear group, and when focusing from an object at infinity to a nearby object, the air distance between both groups is increased, and both groups are moved toward the object side. A lens system capable of photographing glare, a.-, characterized by being moved. 2. In the lens system according to claim 1, f is the composite focal length of the entire system, and f is the focal length of the front, front, and rear groups, respectively. When 1-6<ft/f<3-0...(1) 1, b<
t, 71w<s, o... (2) A lens system capable of photographing close relatives, characterized by satisfying the following condition.