JPH05173064A - Photographic lens - Google Patents

Abstract

PURPOSE:To attain a wide angle while holding the compact formation and high performance of a photographing lens by arranging a negative lens having a convex on the object side as the 1st lens counted from the object side and specifying power relation between a lens group arranged before an iris and a lens group following the iris. CONSTITUTION:The 1st lens counted from the object side is the negative lens having the convex on the object side and the power relation between the lens group arranged before the iris and the lens group following the iris is satisfied with the shown inequality I. In the inequality I, PHIF is the power of the lens group (pre-group) arranged before the iris and PHIR is the power of the lens group (post group) following the iris. Preferably the lens group following the iris consists of a positive lens and a negative lens arranged from the object side and these lenses satisfy the conditions of the shown inequalities II to TV. In the inequalities II to PHIV, f is the power of the 1st lens counted from the object side, PHIl is the power of a negative lens group most close to the image face side, PHI is the power of the whole system, and PHI(+) is the power of a positive lens in the post group.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photographic lens, and more particularly to a wide-angle photographic lens most suitable for a panoramic camera or the like.

[0002]

2. Description of the Related Art In recent years, a lens shutter camera is required to have a wide angle lens. Particularly in panoramic cameras, widening of the angle is strongly desired.

As a conventional wide-angle photographic lens, a retrofocus type often used for a lens for a single-lens reflex camera, a symmetric type such as Topogon, and Japanese Patent Laid-Open No. 58-219509.
Reverse retro type as seen in No. etc. (via the diaphragm,
It is known that the object side lens group has a positive refracting power and the image side lens group has a negative refracting power), and is made compact.

[0004]

However, the retrofocus type is not suitable for downsizing because the back focus is large, and the symmetric type such as the Topogon or the like has a field curvature when it is attempted to downsize and increase the aperture. Is difficult to correct, and it is difficult to achieve high performance. In most of the above-mentioned retro-retro type, the lens group before the diaphragm is composed of three positive, negative, and positive lenses (so-called triplet). Deterioration of (field curvature and astigmatic difference around the screen) cannot be completely corrected by the group after the diaphragm, and eventually it is difficult to achieve high performance.

Therefore, in view of such a situation, an object of the present invention is to provide a photographic lens having a wide angle while achieving compactness and high performance.

[0006]

In order to achieve the above object, the present invention provides a photographic lens having a diaphragm, wherein the first lens from the object side is a negative lens convex toward the object side. It is characterized in that the power relationship between the lens group before and the lens group after the diaphragm satisfies the following conditional expression (1). -0.35 <φF / φR <0.35 (1) where φF: Lens group before the aperture (hereinafter also referred to as “front group”)
Power φR: Lens group after the aperture (hereinafter also referred to as "rear group")
Is the power of.

The conditional expression (1) represents the relationship between the power of the front group and the power of the rear group. If the lower limit of conditional expression (1) is exceeded, the overall length will become longer, and it will not be compact. On the other hand, if the upper limit of conditional expression (1) is exceeded, the power of the front group becomes too large, which makes it difficult to correct aberrations, and the pupil position moves to the image plane side, and the peripheral illuminance decreases.

Further, it is preferable that the lens group after the diaphragm is composed of a positive lens group and a negative lens group from the object side, and the following conditions are satisfied. 0.8 <φl / φf <3.0 (2) -1.5 <φf / φ <-0.2 (3) 1.2 <φ (+) / φ <2.6 (4) where φf: 1 from the object side The first lens (hereinafter "first lens")
(Also called) power φl: Negative lens group closest to the image plane (hereinafter referred to as “final lens group”)
(Also called) power φ: power of the entire system φ (+): power of the positive lens in the rear group.

The conditional expression (2) represents the relationship between the negative power of the first lens and the negative power of the final lens group.
If the lower limit of conditional expression (2) is exceeded, the overall length will become longer, and it will not be compact. On the other hand, if the upper limit of conditional expression (2) is exceeded, the effect of suppressing the curvature of field by the first lens cannot be sufficiently exerted.

The conditional expression (3) is a conditional expression for the negative power of the first lens. If the lower limit of conditional expression (3) is exceeded, the overall length will become longer, and it will not be compact. Also, the conditional expression
When the value exceeds the upper limit of (3), the effect of suppressing the field curvature of the first lens becomes too weak, and the field curvature cannot be suppressed by other lens groups.

If the lower limit of the conditional expression (4) is exceeded, it is impossible to suppress the field curvature from falling to the over side, and if the upper limit is exceeded, the power of the rear group becomes too strong and the total length becomes large.

As the lens configuration, in the front group, a negative meniscus lens having a convex surface on the object side from the object side, a positive lens,
It is desirable to use three lenses, a negative lens or a negative lens whose object side is convex, and a cemented lens made up of a positive lens and a negative lens. Further, in the rear group, it is desirable to form a positive lens group and a negative lens group in order from the object side, and more desirably, a positive lens group,
It is desirable to have a negative lens and a negative meniscus lens concave on the object side.

As the focusing, since the focusing is performed while maintaining high performance up to the proximity, a general whole extension can be adopted.

Next, in the present invention, in order from the object side, the front group is a negative meniscus lens convex to the object side, a cemented lens of a positive lens and a negative lens, or a negative meniscus lens convex to the object side, a positive lens, Preferred conditions in the case of the negative lens configuration will be described. Examples of these configurations include Examples 1 to 4 described later.

It is preferable that the front lens group be configured to satisfy the following conditional expression (5). -2.0 <φS / φ <-0.5 (5) where φS is the power of the surface just before the diaphragm.

If the lower limit of conditional expression (5) is exceeded, the positive power of the second lens (hereinafter also referred to as the "second lens") from the object side becomes too strong, making it difficult to suppress spherical aberration. If the upper limit is exceeded, the overall length becomes longer and the device becomes less compact.

It is desirable that the shape of the first lens element of the negative meniscus lens element convex to the object side should satisfy the following conditional expression (6). 2.5 <(R1 + R2) / (R1-R2) <8.5 (6) where R1: the object side surface of the first lens (hereinafter also referred to as the “first surface”)
Radius of curvature R2: radius of curvature of the image-side surface of the first lens (hereinafter also referred to as “second surface”).

When the lower limit of conditional expression (6) is exceeded, the principal point position of the first lens moves to the object side, effectively increasing the negative power and increasing the total length. If the upper limit of conditional expression (6) is exceeded, spherical aberration will fall to the over side, making correction difficult. Further, the principal point position moves to the image plane side, and the negative power is effectively weakened so that it becomes difficult to suppress the curvature of field.

The following aspherical surfaces are preferably provided in the front lens group. In other words, since the first lens is a negative lens, the second lens has the positive power in the front group, so that the spherical aberration is greatly inclined to the under side, and the lower ray of the off-axis light is increased. It is flipped up and coma easily occurs.
In order to correct this, it is desirable to introduce an aspherical surface into the front group that strengthens the negative power as it goes off-axis, and the amount of deviation of the aspherical surface at that time from the reference spherical surface is
It is desirable to satisfy (7) and (8).

0.1 × 10 ^-4 <| ΔXF (HZ) / F | <0.6 × 10 ^-3 (7) 0.2 × 10 ^-3 <| ΔXF (HM) / F | <0.1 × 10 ^-1 …… (8) where ΔXF (H) is the amount of deviation from the reference spherical surface at a distance H from the optical axis in a plane perpendicular to the optical axis (provided that the image plane side is positive) HZ = 0.4Hmax HM = 0.8Hmax Hmax: Effective diameter of surface F: Focal length of the whole system.

If the lower limits of the conditional expressions (7) and (8) are exceeded, spherical aberration will be greatly tilted to the under side, making correction difficult. When the upper limits of the conditional expressions (7) and (8) are exceeded, the spherical aberration due to the aspherical surface is greatly inclined to the over side, and it becomes difficult to correct other surfaces.

Further, the rear lens group is composed of a positive lens group and a negative lens group from the object side, and more preferably, a positive lens, a negative lens, and a negative meniscus lens concave to the object side, and the following conditional expression (9) It is preferable that the structure satisfies (10). 1.2 <φ (+) / φ <2.5 (9) -0.35 <R (-) / F <-0.15 (10) where R (-) is the object side of the negative lens closest to the image plane. Is the curvature of the surface of.

If the lower limit of conditional expression (9) is exceeded, it will be difficult to prevent the field curvature from falling to the under side, and if the upper limit is exceeded, the power of the rear group will become too strong and the overall length will become long. Becomes less compact.

If the lower limit of conditional expression (10) is exceeded, field curvature will increase and correction will not be possible, and if the upper limit is exceeded, lens manufacture will become difficult.

By adopting a refracting power arrangement such that the front group of the diaphragm has a weak refracting power and the rear group has a strong refracting power while having a shape close to a symmetric type, and by arranging the negative lens group on the image surface side, it is possible to realize an inverse retro. Similarly, a compact optical system is achieved.

In this type of optical system, when the lens closest to the object side is a positive lens, a lens structure desirable for aberration correction as a front lens group is a positive meniscus lens convex to the object side in order from the object side, and a negative meniscus lens. It is a so-called triplet or tesser type having three or four lenses including a lens, a positive lens or a positive cemented lens. However, with this lens configuration, the Petzval sum becomes positively large, and the field curvature increases. Further, the sagittal image plane in the middle band of the screen falls to the under side, and largely falls to the over side around the screen. On the other hand, if you try to eliminate the astigmatic difference in the middle band of the screen by controlling the meridional image, the astigmatic difference around the screen becomes large, and conversely, if you try to correct the periphery, the middle band difference will be It gets bigger. From this, it is understood that when the lens closest to the object side is a positive lens, it is difficult to correct the field curvature and the astigmatic difference, and it is not suitable for widening the angle.

In the present invention, in order to solve this problem, the lens closest to the object side in the front group is a negative lens convex toward the object side. As a result, it is possible to reduce the positive increase of the Petzval sum, and to reduce the tilt of the field curvature to the under side and the astigmatic difference in the periphery of the screen. Furthermore, since this negative lens can reduce the incident angle of the peripheral off-axis light that is incident on the first lens at a large angle after the second lens, correction of other aberrations such as astigmatism separation is also possible. It will be easier to do. Therefore, high performance can be achieved in the entire angle of view. Further, compactness can also be achieved by giving the lens unit on the image side a sufficiently strong negative refractive power.

Further, in a wide-angle and compact lens, a shortage of peripheral light becomes a problem, but since the first lens is a negative lens and the refractive power of the front group before the diaphragm is weak, the pupil position is closer to the object side. It is also possible to output light to the outside, and there is an advantage that a sufficient amount of peripheral light can be obtained.

[0029]

EXAMPLES Examples of the photographic lens according to the present invention will be shown below. However, in each example, ri (i = 1,2,3, ...) is the radius of curvature of the i-th surface counted from the object side, and di (i = 1,2,3, ...) is Shows the i-th axial upper surface distance from the object side,
3, ...), νi (i = 1,2,3, ...) indicates the refractive index and Abbe number of the i-th lens from the object side for the d-line. Also, F
Indicates the focal length of the entire system, and FNO indicates the open F number.

Further, in the examples, the surface with a radius of curvature marked with * indicates that it is a surface composed of an aspherical surface, and the expression of the following numerical expression 1 representing the surface shape (f (r)) of the aspherical surface is shown. Shall be defined in.

<Example 1> F = 24.3 FNO = 3.62 [radius of curvature] [axis upper surface spacing] [refractive index] [Abbe number] r1 * 12.628 d1 1.100 N1 1.51680 ν1 64.20 r2 6.949 d2 3.100 r3 11.623 d3 3.800 N2 1.77250 ν2 49.77 r4 -13.598 d4 1.200 N3 1.61293 ν3 37.01 r5 12.081 d5 1.600 r6 ∞ (diaphragm) d6 2.000 r7 32.327 d7 3.000 N4 1.67000 ν4 57.07 r8 -12.386 d8 0.100 r9 28.766 d9 1.000 N5 1.75520 10.15 57.410 r5 27.51 r. d11 1.300 N6 1.58340 ν6 30.23 r12 * -8.824

[Aspherical surface coefficient] r1: ε = 0.14628 × 10 A4 = −0.89294 × 10^-Four  A6 = -0.35628 x 10^-6  A8 = -0.14122 x 10^-7  A10 = 0.15811 x 10^-Ten  A12 = 0.42788 × 10^-12  r12: ε = -0.73340 A4 = -0.30091 × 10^-3  A6 = -0.18131 x 10^-Five  A8 = 0.76368 x 10^-8  A10 = -0.23897 × 10^-9  A12 = -0.40337 × 10^-11

<Example 2> F = 24.3 FNO = 3.62 [radius of curvature] [axis upper surface spacing] [refractive index] [Abbe number] r1 10.653 d1 1.100 N1 1.51680 ν1 64.20 r2 * 6.616 d2 2.300 r3 11.602 d3 2.500 N2 1.77250 ν2 49.77 r4 -14.545 d4 1.200 N3 1.61293 ν3 37.01 r5 13.005 d5 1.600 r6 ∞ (aperture) d6 2.000 r7 -434.556 d7 2.000 N4 1.65160 ν4 58.60 r8 -8.946 d8 0.900 r9 340.316 d9 1.000 N5 1.75520 1037 37259.10 r. 6.191 d11 1.300 N6 1.58340 ν6 30.23 r12 * -8.907

[Aspherical surface coefficient] r2: ε = 0.13026 × 10 A4 = 0.33854 × 10^-Four  A6 = -0.58533 x 10^-6  A8 = 0.54504 x 10^-7  A10 = 0.45881 × 10^-9  A12 = 0.25775 × 10^-11  r12: ε = -0.12051 × 10 A4 = -0.39044 × 10^-3  A6 = -0.94780 x 10^-6  A8 = -0.16059 x 10^-8  A10 = -0.99103 × 10^-Ten  A12 = -0.56521 × 10^-11

<Example 3> F = 24.3 FNO = 3.62 [radius of curvature] [axis upper surface spacing] [refractive index] [Abbe number] r1 6.536 d1 1.100 N1 1.51680 ν1 64.20 r2 5.001 d2 2.700 r3 * 13.403 d3 2.400 N2 1.77250 ν2 49.77 r4 -15.648 d4 1.200 N3 1.61293 ν3 37.01 r5 11.417 d5 1.600 r6 ∞ (diaphragm) d6 2.000 r7 -8922.992 d7 2.000 N4 1.65160 ν4 58.60 r8 -7.913 d8 0.900 r9 -102.940 d9 1.000 N5 1.75520 105311 527.52710. -6.505 d11 1.300 N6 1.58340 ν6 30.23 r12 * -9.198

[Aspherical surface coefficient] r3: ε = -0.39913 A4 = -0.11515 × 10^-Four  A6 = -0.11100 x 10^-Five  A8 = 0.35285 x 10^-8  A10 = 0.14204 × 10^-9  A12 = 0.10386 × 10^-11  r12: ε = -0.71598 A4 = -0.25097 × 10^-3  A6 = -0.15820 x 10^-Five  A8 = 0.10035 × 10^-7  A10 = -0.10 220 × 10^-9  A12 = -0.24607 × 10^-11

<Example 4> F = 24.3 FNO = 3.62 [radius of curvature] [axis upper surface spacing] [refractive index] [Abbe number] r1 9.390 d1 1.100 N1 1.61293 ν1 37.01 r2 5.809 d2 2.300 r3 9.683 d3 2.300 N2 1.77250 ν2 49.77 r4 32.231 d4 0.800 r5 21.553 d5 1.000 N3 1.61293 ν3 37.01 r6 10.559 d6 1.600 r7 ∞ (aperture) d7 2.000 r8 49.571 d8 2.000 N4 1.65160 ν4 58.60 r9 -9.459 d9 0.900 r5 122.532 d10 1.000 N5 1.7511 r5 2 -6.180 d12 1.300 N6 1.58340 ν6 30.23 r13 * -8.417

[Aspherical surface coefficient] r13: ε = -0.57412 A4 = -0.31295 × 10^-3  A6 = -0.37665 x 10^-6  A8 = -0.35 150 × 10^-7  A10 = 0.47485 × 10^-Ten  A12 = -0.24851 × 10^-11

FIG. 1, FIG. 3, FIG. 5 and FIG. 7 are lens configuration diagrams corresponding to Examples 1 to 4, respectively.

In the first embodiment, in order from the object side, a front lens group consisting of a negative meniscus lens convex to the object side and a cemented lens composed of a biconvex positive lens and a biconcave negative lens, and a diaphragm (S).
And a rear group consisting of a biconvex positive lens, a negative meniscus lens concave on the image side, and a negative meniscus lens concave on the object side. The object-side surface of the negative meniscus lens in the front group and the image-side surface of the negative meniscus lens in the rear group are aspherical surfaces.

In the second embodiment, in order from the object side, a front lens group consisting of a negative meniscus lens convex to the object side and a cemented lens composed of a biconvex positive lens and a biconcave negative lens, and a diaphragm (S).
And a rear group including a positive meniscus lens having a convex surface on the image side, a negative meniscus lens having a concave surface on the image side, and a negative meniscus lens having a concave surface on the object side. The image side surface of the negative meniscus lens in the front group and the image side surface of the negative meniscus lens in the rear group which is concave on the object side are aspherical surfaces.

In the third embodiment, in order from the object side, a front lens group consisting of a negative meniscus lens convex to the object side and a cemented lens composed of a biconvex positive lens and a biconcave negative lens, and a diaphragm (S).
And a rear group including a positive meniscus lens having a convex surface on the image side, a biconcave negative lens, and a negative meniscus lens having a concave surface on the object side. The object side surface of the biconvex positive lens element in the front group and the image side surface of the negative meniscus lens element concave in the rear group are aspherical surfaces.

The fourth embodiment includes, in order from the object side, a front group consisting of a negative meniscus lens convex to the object side, a positive meniscus lens convex to the object side, and a negative meniscus lens concave to the image side,
It is composed of a stop (S), a biconvex positive lens, a negative meniscus lens concave to the image side, and a rear group consisting of a negative meniscus lens concave to the object side. The image-side surface of the negative meniscus lens concave in the rear group toward the object side is aspherical.

2, FIG. 4, FIG. 6 and FIG. 8 are aberration diagrams corresponding to Examples 1 to 4, respectively. The solid line (d) is d
It represents the aberration with respect to the line, and the broken line (SC) represents the sine condition. Further, the broken line (DM) and the solid line (DS) represent astigmatism on the meridional surface and the sagittal surface, respectively.

Table 1 shows φl / φf in conditional expression (2), φF / φR in conditional expression (1), and conditional expressions in Examples 1 to 4
Φf / φ in (3) and φ (+) / φ in conditional expressions (4) and (9) are shown. Table 2 shows R in the conditional expression (10) in Examples 1 to 4.
(-) / F, φS / φ in conditional expression (5), (R1 + R in conditional expression (6)
2) / (R1-R2) is shown.

Table 3 shows conditional expressions (7),
The value (Dev / F) regarding the amount of deviation about the aspherical surface (1st surface, 2nd surface, 3rd surface and 12th surface) corresponding to (8) is shown.

[0047]

[Equation 1]

[0048]

[Table 1]

[0049]

[Table 2]

[0050]

[Table 3]

[0051]

As described above, according to the present invention, the first lens element from the object side has a negative lens element convex to the object side as the first lens element. By making the correction favorably and satisfying the conditional expression (1), the aberration can be favorably corrected and the compactness can be achieved. Therefore, it is possible to realize a photographic lens having a wide angle while achieving compactness and high performance.

Further, by adopting a constitution that satisfies the above conditional expressions (2) to (4), while satisfactorily correcting the field curvature,
Further compactness can be achieved.

[Brief description of drawings]

FIG. 1 is a lens configuration diagram of a first embodiment of the present invention.

FIG. 2 is an aberration diagram of Example 1 of the present invention.

FIG. 3 is a lens configuration diagram of a second embodiment of the present invention.

FIG. 4 is an aberration diagram of Example 2 of the present invention.

FIG. 5 is a lens configuration diagram of a third embodiment of the present invention.

FIG. 6 is an aberration diagram of Example 3 of the present invention.

FIG. 7 is a lens configuration diagram of a fourth embodiment of the present invention.

FIG. 8 is an aberration diagram of Example 4 of the present invention.

[Explanation of symbols]

 (S)… Aperture

Claims (2)

[Claims] 1. A photographic lens having a diaphragm, wherein the first lens from the object side is a negative lens convex toward the object side, and the power of a lens group before the diaphragm and a lens group after the diaphragm. Photographic lens characterized by satisfying the following conditions: -0.35 <φF / φR <0.35 where φF is the power of the lens group before the diaphragm φR is the power of the lens group after the diaphragm. 2. The photographic lens according to claim 1, wherein the lens unit after the diaphragm is composed of a positive lens unit and a negative lens unit from the object side, and the following conditions are satisfied: 0.8 <φl / φf <3.0 -1.5 <φf / φ <-0.2 1.2 <φ (+) / φ <2.6 where φf is the power of the first lens from the object side φl is the power of the negative lens group closest to the image side φ: Power of entire system φ (+): Power of the positive lens in the rear group.