JPS6053847B2 - front aperture lens - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a front diaphragm lens, and more particularly to a front diaphragm lens that includes only three lenses but covers a standard angle of view of 460 or more.

In small cameras, it is often desirable for the aperture to be located outside the lens (in front or behind the lens) due to structural constraints.

In particular, with front aperture lenses, unlike normal lenses, the lens is arranged significantly asymmetrically with respect to the aperture.
It has been difficult to correct astigmatism, coma, and the like.

Therefore, it is an object of the present invention to provide a front diaphragm lens having technical means for solving the above-mentioned difficulties.

This technical means is to apply conditions 1 to 6 of the lens structure and each parameter.

Conditions 1 to 2 will be explained below. 10.37<5
<0.44 is a condition regarding the total length of the lens including the aperture, and takes into account the need to ensure peripheral light intensity while making the lens small and to correct aberrations.If S exceeds the upper limit, a decrease in peripheral light intensity is prevented. Therefore, the lens L3 becomes large.

. Furthermore, if S exceeds the lower limit, the refractive powers of the lenses L, 1-, and L3 will become too strong, making it difficult to properly correct aberrations. ⌒ 0.8 < Go 0.95 is the sixth
This is a condition for configuring the surfaces to be nearly concentric and properly correcting astigmatism, and is set in consideration of the balance with correction of other aberrations.

In other words, if the upper limit of this condition is exceeded, the correction effect of the refractive index number N01.88300vl40.9 N21.71736ri229.5 N31.69350V353.4 for the astigmatism line becomes insufficient. If the lower limit is exceeded, the spherical aberration generated at the sixth surface becomes excessive and difficult to correct.

30.025<d2<0.04ゝ40.03<d0<0
．． 07 and 0.0Kd, <0.15 are conditions for satisfactorily correcting various aberrations, particularly coma flare in the upper part of the oblique light beam, while satisfying Condition 1.

That is, if the upper limit of these conditions is exceeded, the off-axis light beam passes through the peripheral part of the lens, making it difficult to correct comatic aberration, and if the lower limit is exceeded, the lenses L, L, and L.

The refractive power becomes excessive, making it difficult to correct all aberrations.
This is because in the front diaphragm lens, the light beam passes through the lens L2 in a biased manner, compared to a lens in which the diaphragm is located inside the lens.

Although coma flare is likely to occur due to the strong refractive effect of the lens, the above-mentioned coma flare can be eliminated by providing an appropriate distance between the fourth surface and the fifth surface according to conditions 3 to 3. 1.77<N is a condition for flattening the image plane by reducing the Petzval sum.If the lower limit of this condition is exceeded, the Hetzval sum increases and the curvature of the image increases. This is effective when the distance between each lens is small, as in

The present invention will be described below based on preferred embodiments shown in the accompanying drawings.

FIG. 1 is a lens arrangement diagram for implementing the present invention, including a biconvex lens L2 with a surface with a strong curvature facing the object side, and a biconvex lens L2.
and a convex meniscus lens L3 with a convex surface facing the image side, where the distance from the aperture to the sixth surface is S), the radius of curvature of the sixth surface is rf, Li and L3.

4. The front diaphragm lens according to claim 1, which comprises the lenses shown in the table below.

5. In the front diaphragm lens according to claim 1,
Detailed description of the front diaphragm lens ZO invention consisting of the lenses shown in the table below. However, the present invention relates to a front aperture lens that covers 46 or more standard angles of view.

In small cameras, it is often desirable for the aperture to be located outside the lens (in front or behind the lens) due to structural constraints.

In particular, with front aperture lenses, unlike normal lenses, the lens is arranged significantly asymmetrically with respect to the aperture.
It has been difficult to correct astigmatism, coma, and the like.

Therefore, it is an object of the present invention to provide a front diaphragm lens having technical means for solving the above-mentioned difficulties.

This technical means is to apply conditions 1 to 5 of the lens structure and each parameter.

Conditions 1 to 5 will be explained below. 10.37kuS
0.44 is a condition related to the total length of the lens including the aperture, and takes into consideration securing peripheral light intensity while making the lens small and correcting aberrations.If S exceeds the upper limit, it will prevent the peripheral light intensity from decreasing. Therefore, the lens L3 becomes large.

．． Furthermore, if S exceeds the lower limit, the refractive powers of the lenses Ll, I-, and L3 will become too strong, making it difficult to properly correct aberrations. 20.8〈↓凰〈0.95 is a condition for configuring the 6th surface concentrically and close to the aperture to properly correct astigmatism, and also balances the correction of other aberrations. This setting was taken into consideration.

In other words, if the upper limit of this condition is exceeded, the astigmatism correction effect will be insufficient, and if the lower limit is exceeded, the sixth surface (R6)
The spherical aberration generated in this case becomes excessive and difficult to correct.

30.025〈D2ku0.04\40.03kuD4ku0
．． 07 and 50.09<D, and 0.15 are conditions for satisfactorily correcting various aberrations, particularly coma flare in the upper part of the oblique light beam, while satisfying Condition 1.

In other words, if the upper limit of these conditions is exceeded, the off-axis light beam passes through the peripheral part of the lens, making it difficult to correct coma aberration, and if the lower limit is exceeded, the refractive power of lenses Ll, L, and L3 becomes excessive, causing aberrations. General correction becomes difficult.

With a front diaphragm lens, compared to a lens with a normal diaphragm inside the lens, the light beam passes through the lens L2 in a biased manner, so coma flare is more likely to occur due to the strong refraction effect at R4. Due to conditions 3 to 5, the fourth
By providing an appropriate distance between the surface and the fifth surface, the above-mentioned coma flare can be eliminated.

61.77 N1 is a condition for flattening the image plane by reducing the Petzval sum.If the lower limit of this condition is exceeded, the Hetzval sum increases and the curvature of the image increases. This is effective when the distance between each lens is small, as in the case of this method.

The present invention will be described below based on preferred embodiments shown in the accompanying drawings.

FIG. 1 is a lens arrangement diagram for implementing the present invention, including a biconvex lens L2 with a surface with a strong curvature facing the object side, and a biconcave lens L2.
It consists of a convex meniscus lens L3 with the convex surface facing the image side, and the distance from the aperture to the sixth surface is S1 the radius of curvature of the sixth surface! , the distance between L1 and L2 is D2, the distance between L2 and L is D4, the center thickness of L3 is 4, the refractive index of L1 is N1, and the focal length of the entire system is 1, the following conditions are satisfied. It is something.

Each parameter of this example is shown in Table 1, and various aberrations with these parameters are shown in FIG. In B, the solid line shows sagittal astigmatism and the broken line shows meridional astigmatism, respectively.

It is clear from this example that various aberrations are well corrected despite the simple three-element structure.

Next, the second, third and fourth embodiments which can achieve the same effects as the above embodiments are shown in FIGS. 3, 5 and 7.
The parameters of these examples are shown in Tables 2, 3 and 4, and the various aberrations are shown in Figs.
and FIG. 8, respectively. Here, in these aberration curve diagrams, the same symbols and lines as in FIG. 2 indicate the same aberrations. In these embodiments, the same reference numerals as in the first embodiment indicate the same agents.

As is clear from the above explanation and the aberration curve diagram, the lens of the present invention has a simple three-element structure, but aberrations are well corrected, and the front aperture lens is extremely compact and has good performance. can be provided.

[Brief explanation of drawings]

1, 3, 5 and 7 are lens arrangement diagrams of the first, second, third and fourth embodiments, respectively;
, FIG. 4, FIG. 6, and FIG. 8 are aberration curve diagrams of the above embodiments, respectively.

Claims (1)

[Claims] 1. A biconvex lens L_1 with a surface with a strong curvature facing the object side,
In the front aperture lens, which is composed of a biconcave lens L_2 and a convex meniscus lens L_3 with a convex surface facing the image side, and has both angles of 46° to 50° and an aperture ratio of 3.5, the sixth lens from the aperture
The distance to the surface is S, the radius of curvature of the 6th surface is r_6, L_1
The distance between L_2 and L_2 is d_2, and the distance between L_2 and LC is d_2.
_4, center thickness of L_3 is d_5, refractive index of L_1 is N_
1. When the focal length of the entire system is 1, the following condition (1) 0
．． 37<S<0.44 (2) 0.8<|r_6|/S
<0.95(3)0.025<d_2<0.045 (
4) 0.03<d_4<0.07 (5) 0.09<d_
5<0.15 (6) A front aperture lens satisfying 1.77<N_1. 2. The front diaphragm lens according to claim 1, which comprises the lenses shown in the table below. ▲There are mathematical formulas, chemical formulas, tables, etc.▼ 3. The front diaphragm lens according to claim 1, which comprises the lenses shown in the table below. ▲There are mathematical formulas, chemical formulas, tables, etc.▼ 4. The front diaphragm lens according to claim 1, which comprises the lenses shown in the table below. ▲There are mathematical formulas, chemical formulas, tables, etc.▼5 The front diaphragm lens according to claim 1, which comprises the lenses shown in the table below. ▲Contains mathematical formulas, chemical formulas, tables, etc.▼