JPS5913210A - Wide angle lens - Google Patents

Abstract

PURPOSE:To extend a back focus and to obtain a necessary F number and a necessary angle of view by compensating respective aberrations including a lens as the 1st component contacting with water on specific condition. CONSTITUTION:The radii of curvature of the image-side lens surfaces of the 1st, the 3rd, and the 4th components L1, L3, and L4 of the lens are r2, r6, and r8, and the radii of curvature of the object-side and image-side lens surfaces of the 6th component L6 are r11 and r12; and the focal lengths of the 3rd and the 4th components L3 and L4 are f3 and f4, and the distance on the axis from the image-side lens surface of the 1st component L1 to the object-side lens surface of the 5th component L5 is D. In this case, inequalities are satisfied. Consequently, a wide angle lens having, for example, a 90-100 deg. angle of view, F number 2.8, and a long back focus is obtained.

Description

Detailed Description of the Invention The present invention has an angle of view of 9'06 to 100 degrees, an F number of 2, and 8K.
The present invention relates to a wide-angle lens J with an amazing back focus, especially for use underwater.

Conventionally, underwater wide-angle lenses with an angle of view of 90° to 100° and an F number of 2.8 are known that use a symmetrical lens with a convex-convex aperture as a mask lens, but the back focus is 0.55 f. (f: focal length of the entire system), which can cause problems when a long back focus is required to install a photometry mechanism or a quick return mirror in a single-lens reflex camera between the lens and the image plane. Ta. Further, as a general aerial photography lens having an angle of view exceeding 90°, a lens using a retrofocus type is known, and this is suitable for the purpose of increasing the back focus. However, when used underwater, the refractive index of the physical world changes, so the refraction of light rays entering the lens from water changes, resulting in fluctuations in aberrations, making it impossible to obtain optimal optical performance.

Another known method is to attach a concentric spherical window centered at the entrance pupil position to the front of the lens for in-wall photography, but this method has the advantage of not changing the angle of view and causing no lateral chromatic aberration. On the other hand, as shown in FIG. 1, since the surface 1a of the spherical window 1 in contact with the air has a diverging effect, the object plane becomes a spherical virtual image P with its concave surface facing the lens 2, and the lens 2 creates a 18! As shown in the figure, Q has a positive field convergence theme as a whole.

Furthermore, it is desirable to make the diameter smaller in order to improve water pressure resistance and make the lens more compact, but the smaller the radius of curvature of the spherical window, the stronger the curvature of field aberration occurs, and the angle of view becomes 9.
A wide-angle lens with an angle of more than 0° deteriorates peripheral images, making it unusable.

An object of the present invention is to provide an underwater wide-angle lens with a back focus of 1.4 f or more, an angle of view of 90° to 100°, and a well-balanced aberration that reaches an F number of 2.8.

In consideration of the above-mentioned difficulties, the present invention is capable of sufficiently correcting each aberration, including the one-component lens in contact with water, under various conditions. Specifically, in order from the object side, the first component L1 has a convex surface on the image side facing the object side, and the second component M has a positive meniscus lens with a convex surface facing the object side.
, minutes L2, the third component of the negative meniscus lance "ms, the fourth component L4 of the negative meniscus lance are arranged, and the components L1, L1~
L3. L-L4 form a diverging system, and then the fifth component of the stop lens is the 6th rJ′i of the I1 double-convex positive lens, and the minute Ls
and the seventh of the negative sign and zu with the concave surface facing the object side.
The eighth component Ls is a positive meniscus lens with a concave surface facing the object side, and the ninth component L9 is a pneumatic lens with a convex surface facing the image side. The radius of curvature of the image side lens surface of each of the four components is
'! ,'@,rs, the radius of curvature of the object-side and image-side lens surfaces of the sixth component is r'''11 and rt's, respectively,
The focal lengths of the third and fourth components are respectively f8.
, '4sWhen the axial distance from the image-side lens surface of the first component to the object-side lens surface of the fifth component is D, a wide-angle lens whose % characteristic is to satisfy the following conditions. That's what I did.

(1) 0.6<fs/ f4<1.7(2) r
s>rs (3) ro >1.51 ru I (4) 0.
6<rm/D<1.2 Each condition will be described in more detail below.

Condition (1) defines the ratio of the focal lengths of the lenses of the third component Ls and the fourth component L4. Each lens of the third component L3 and the fourth component L4 is.

It has a mechanism that gradually diverges the light rays incident parallel to the optical axis and lengthens the back focus, but in order to lengthen the back focus, strong power is required, and for this purpose the entire optical system Lower-air distortion and overcorrected spherical aberration tend to remain. In order to achieve good aberration correction, it is preferable to suppress this tendency as much as possible. It is desirable to keep the focal length ratio of L4 close to 1. Condition (1) exceeds the upper limit and the third
When the refractive power (reciprocal of the focal length) of the lens of component L3 becomes relatively small, the effect of reducing the back focus of the thin lens becomes weaker, and the required back focus cannot be obtained. In addition, since a ray incident parallel to the optical axis is diverged at the a tq component, the 11g4 component L4 is incident at a distance farther from the optical axis, but the refraction of the fourth component L4 is relatively Since the force is large, it is strongly influenced by the divergence caused by the fourth component L4, and spherical aberration occurs overcorrection and cannot be corrected. On the other hand, if the lower limit of condition (1) is exceeded, it is advantageous to obtain back focus, but the position of incidence on the third component L4 of the oblique light ray is from the multiple optical axes compared to that of the fourth component L4. Because it is located far away, it is relatively
Negative distortion aberration due to the increased refractive power of component Lm increases and cannot be corrected.

Condition (2) expresses the diverging effect of the oblique ray with the third component L3 and the fourth component L3.
This is a conditional expression that satisfactorily corrects the field curvature aberration of the optical system by having the component L4 share the function. Since both components have a strong divergent effect, they tend to cause positive field curvature aberration in the general sum optical system, but r6〉r shown in condition (2)
Depending on the condition of s, the divergence effect is caused by the third component L1 and the fourth bX
, t, and 41c, it is now possible to correct the field curvature aberration of the optical system in a well-balanced manner. If condition (2) does not hold and the relative KM becomes small, the divergence effect on this surface becomes excessive and the curvature of field aberration becomes overcorrected and cannot be corrected.

Condition (3) is a conditional expression for correcting coma aberration.

The oblique rays are subjected to a diverging effect by the third component L4 and the fourth component L4; Sycoma aberration occurs when light rays passing below are subjected to a particularly strong divergent effect. Condition (3) provides a strong convergence effect to the sixth component L#I by limiting the radius of curvature of the sixth component L6 of the positive lens, thereby correcting coma aberration. If condition (3) is not satisfied and the radius of curvature Ir+nl of the image-side lens surface becomes relatively large, the convergence effect of this surface on the lower side of the oblique light beam becomes weak p.

If the divergence effect of the third and fourth components 111sL4 is relatively strong, coma aberration cannot be corrected.

Condition (4) defines the radius of curvature of the image-side lens surface of the first component L1 with respect to the sum of the lens surface spacings d to d8 regarding the lens components L1 to L4 that form a divergent group as a whole. When the value of the radius of curvature r3 of the image side lens surface of the first component L1 is a relatively large value, the divergence effect on this surface becomes small for oblique rays, so that they are less likely to occur in the entire optical system. Although it is advantageous for correcting positive field curvature aberration, the back focus is short and it is necessary to strengthen the divergence effect of the third and fourth components Ls%L4 in order to extend it to the required value. occurs, and higher-order aberrations are more likely to occur. If condition (4) exceeds the upper limit, strong comatic aberration will occur over the entire screen due to the strong divergence effect of the 3rd and 4th components, L4, but the convergence effect will not be exerted within the lens system. Even if the coma aberration at the periphery of the screen is corrected by strengthening the effect of the surface, the coma aberration at intermediate angles of view will not be corrected in a well-balanced manner due to the influence of the ^-order difference.

The radius of curvature r of the image side lens surface of the first component L1.

When the value of is relatively small, it is advantageous to obtain a long back focus, but since the divergence effect of oblique rays becomes stronger at this surface, positive field curvature aberration increases. If condition (4) exceeds the lower limit, positive field curvature aberration will occur, but field curvature will be particularly noticeable at the periphery of the screen, and the field curvature aberration at intermediate field angles will need to be corrected using other methods. Even if it were possible to do so, positive field curvature aberration remains at the periphery of the screen and cannot be corrected satisfactorily.

The basis for conditions (1) to (4) has been described above, but the wide-angle lens according to the present invention maintains coma aberration well, especially coma aberration M in the upper east side of the oblique light (rays passing above the center of the aperture). As a condition, when the focal length of the seventh component L1 is 'Y, and the radius of curvature of the image side lens surface is r1''4, -
It is desirable to satisfy 5,0<r/f7(-1,5).

Especially the upper side of the oblique light beam has the eighth and ninth components Lm, L
However, the image-side surface r14 of the seventh component L1 has a diverging effect, especially on the upper side of the oblique light beam, and balances and corrects the coma aberration. If the upper limit of this condition is exceeded, the divergence effect will be weakened,
If the lower limit is exceeded, the divergence effect is too strong, and coma aberration cannot be corrected well in either case.

Next, embodiments according to the present invention will be described.

In general, underwater lenses do not use a system that extends the entire lens because it is advantageous in terms of waterproof and water pressure resistant structure, but the distance is adjusted by fixing the front group lens.

In the first embodiment shown in FIG. 2, the first component Ll is fixed, and the second to ninth components, ~t, and e, can be delivered as one unit. In this case, by extending the lens components L3 to L-, the entrance pupil position approaches the first component L19, and since the incident height of the oblique ray approaches the optical axis, the curvature of field aberration becomes negative. point in a direction. In general, retrofocus type lenses have a strong tendency for positive field curvature to occur at short distances, and this is the first step in correcting this positive field curvature.
It is advantageous to keep the component L1 fixed and to feed out the lens components Ls-L as one unit.

The lens configurations of the second and third embodiments of the present invention are shown in FIGS. 3 and 4, respectively. In both embodiments, the first component L
1 to 3 components.

up to a fixed front group, and the fourth and subsequent components L4 to L9 are integrated to form a rear group, and by extending this, it is possible to perform close-range photography. As the entrance pupil position approaches the third component, it also has the function of correcting fluctuations in field curvature aberration, as described in the first embodiment.

In the first embodiment, as shown in FIG.
Component Ll is composed of a negative meniscus lens with a convex surface facing the object side and a biconvex lens bonded together. In the second embodiment, as shown in FIG. 3, the fifth component of the positive lens is composed of a combination of three lenses: a biconvex lens, a biconcave lens, and a biconvex lens, and the seventh component L1 of the negative lens is on the image side. It is composed of a positive meniscus lens with a convex surface facing toward the side and a biconcave lens.

In addition, in the third embodiment, as shown in FIG. 4, the second component of the positive meniscus lens is a combination of a negative meniscus lens with a convex surface facing the object side and a positive meniscus lens with a convex surface facing the object side. The fifth component L8 of the positive lens is composed of a negative meniscus lens and a biconvex lens, similar to the first embodiment, and the seventh component L1 of the negative lens is composed of a negative meniscus lens and a biconvex lens, similar to the second embodiment. It is constructed by laminating a positive meniscus lens and a biconcave lens.

The specifications of each example are shown below. However, rl, rl (i
'ms'... is the radius of curvature of each lens surface in % from the object side '*s dl= dl s '... is the center thickness and spacing of each lens, fJ, n1%11g... and ν, νhν [1... is the d[λ=5 of each lens]
87.6 nm) and 7-tube number.

to oO oo prisoner
To the edge of OCO
C dimension 11+1 W I
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■Φ Dimension cQw t+
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M B I N I l'
l If 1, a55a-t'-oo c.

clll(ORIIN m l Q Lo Φ ■ 口Φtoch% Lo cQ He - ・-ItMIfI
IIf parable oo to o to todo's ω Roro (Fj (rl Ot'- Dimension - 1- to Dimension 1 Li-1 + 1 1 -II II N 'II M I I
If 阿55- ψto groan ro 0 ■ 1:r1'”'a1～-roC'QC1v-1m
IJ II It It It
II II I decrease ′,
CI"CI "c3"c3't3"CI-
c3 勺 11, a, a
,! rJ,! i
,,! i Zeng An ■ IQ Rid 5 '5 1 Various of the above examples 74) 4. The difference diagrams are shown in FIG. 5 (first embodiment), FIG. 6 (second embodiment), FIG. 7 (third embodiment), respectively. From each station and the difference diagram, it is clear that all examples have an angle of view of 96° and an F number of 2.8, and also have a sufficiently long grasshopper focus and excellent imaging performance. be.

In addition, the above-mentioned 1st to 3rd examples were entered in the data table as lenses exclusively for underwater use. Although aberration correction has been performed on the value of Osν, it can be used not only in fresh water but also in seawater, alcohol, and ether.Refractive index n in object space.

is 1.2 (no<1.4), each embodiment can be put to practical use as is.

As described above, according to the present invention, the back focus is 1.4 f or more, the angle of view is 90° to 100°, and the F number is 2.
．． It is possible to obtain an underwater wide-angle lens with an excellent aberration balance of 8.

[Brief explanation of drawings]

Fig. 1 is a conceptual diagram for explaining the present invention, Fig. 2', Fig. 3, and Fig. 4 are lens configuration diagrams showing embodiments 1-7 and 3 of the present invention, respectively. Fig. 5 . FIGS. 6 and 7 each show four different aberrations of the first to third embodiments described above. ■Explanation of symbols of main parts] L1 to L---Lens component l"""s f4...Focal length r of lens component
l , rs $1) # rll * rlm ``' Radius of curvature of the lens surface, D... Axial distance Fang 3 Figure L + Figure 5 Coma power and envy Figure 6 Coma'' and difference

Claims (1)

[Claims] The first ml of the image side facing from the object side to the face is a convex pot facing the object side.
Component L1, second component L*sjL of a positive meniscus lens with each convex surface facing the object side, third component L of a meniscus lens
ss 4th component L of a negative meniscus lens 4 s 5th component of a positive lens Is 6th component L of a biconvex positive lens, 7th component Lt of a negative lens with a concave surface on the object side, concave surface facing the object side an eighth component L of a positive meniscus lens having a convex surface on the image side, and a radius of curvature of the image side lens surface of each of the first component, third component, and fourth component; are respectively rlsrl!
When the focal length of the component is ``fs%''4s, respectively, and the axial distance from the image-side lens soffit of the first component to the object-side lens surface of the #5 component is D, the following conditions must be satisfied. f: Wide-angle lens in percentage. (1), 0..6<f, s/f4<1.7(2)
r @ ) r , @ (3) r ■ > 1.51 rts 1 (430,6
< r 禦 / D < 1.2