JPH09211320A - Small-sized wide-angle lens - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a small-sized wide-angle lens of simple constitution which has high performance of a nearly 1.0 telephoto ratio, a 2.8 FNO class, and a view angle exceeding 70 deg. and also has mass-productivity. SOLUTION: This optical system is a telephoto type wide-angle lens consisting of a Tessar type front group, a stop, and a rear group which is a negative meniscus lens having its convex surface on an image side. The 3rd surface R3 and 7th surface R7 in the front group I and the 8th surface R8 in the rear group II are aspherical surfaces. The range of the refracting action of the 1st surface R1 , the range of the refracting action of the cemented surface of the cemented lens3.4 , the range of the refracting power of the 5th lens L5 in the relation with the refracting power of the whole system, the range of the sum 'd7 +d8 ' of the air gap across the stop S, and the shape of the 5th lens L5 are adequately prescribed to both hold the telephoto rate small and excellently compensate various aberrations and the Petzval's sum, and also both improve the optical performance and reduce the size.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a compact wide-angle lens, and more specifically, has a telephoto ratio of 1.0 and an F _No. of 2.
The present invention relates to a small-sized wide-angle lens having a large aperture and an eighth-class angle of view exceeding 72 °.

[0002]

2. Description of the Related Art For example, a lens shutter camera (LSC)
As a photographing lens for use in the field of view, an optical system having a wide angle of view, a telephoto ratio of about 1.0, and a certain degree of brightness and having a simple optical system configuration is desired. . Therefore, in order to meet these demands, various optical systems have already been proposed, such as those disclosed in Japanese Patent Publication No. 4-43245 and Japanese Patent Publication No. 4-26443, or Japanese Patent Laid-Open No. 3-265809. Has been done.

[0003]

[Problems to be solved by the invention]
The optical system disclosed in Japanese Patent Publication No. 4-43245 has a telephoto ratio of about 1.0 and an F _No. of 2.8, which satisfies the above-mentioned demands regarding the telephoto ratio and F _No. Therefore, although the demand for an optical system having a simple structure is almost satisfied, the angle of view is as narrow as 63 °, which is a drawback of this optical system. The optical system disclosed in Japanese Patent Laid-Open No. 3-265809 has an F _No. of 2.8 and satisfies the demand for brightness, but has a narrow angle of view of 65 °. It is not an optical system that meets all the needs.

On the other hand, the optical system disclosed in Japanese Examined Patent Publication (Kokoku) No. 4-26443 satisfies the demand for the angle of view of 70 ° class, but the F _No. is as dark as 4.0 _. This is a major drawback of optical systems. In short, the present situation is that no wide-angle lens that satisfies all the above-mentioned demands has been proposed yet. The present invention has been made in view of such circumstances, and its object is to achieve a compact size with a telephoto ratio of about 1.0, an F _No. of 2.8 class, and an angle of view of more than 72 °. Each aberration is excellently corrected while having a large aperture performance, and it is possible to maintain its high performance even when the shooting distance changes. Furthermore, it is compact with mass production and has a simple configuration. To provide a wide-angle lens.

[0005]

In order to achieve the above object, the invention according to claim 1 is a positive meniscus lens having a convex surface facing the object side, which is arranged in order from the object side. A lens, a second lens that is a biconcave lens, a front lens group that includes a cemented lens in which a third lens that is a negative lens having a concave surface facing the image side and a fourth lens that is a biconvex lens are bonded together, a diaphragm, and a convex surface. An optical system of four-group, five-lens structure including a rear group composed of a fifth lens which is a negative meniscus lens facing the image side, and at least one surface of at least one lens in the front group. Is formed as an aspherical surface,
At least one surface of the fifth lens is formed as an aspherical surface having a diverging action that weakens toward the periphery, and
The focal length of the entire system is f, the focal length of the fifth lens is f ₅ , the radius of curvature or paraxial radius of curvature of the i-th lens surface counting from the object side is R _i , and the i-th and i + 1-th counting from the object side. When the on-axis distance from the surface of the lens is d _i and the refractive index of the j-th lens counted from the object side is n _j , (3) 0.8 f <| f ₅ | <1.2 f (4) 0.25 f <d ₇ + d ₈ <0.45 f It is characterized in that each conditional expression is satisfied.

According to a second aspect of the invention, the first lens, which is a positive meniscus lens having a convex surface facing the object side, the second lens which is a biconcave lens, and the concave surface are imaged, which are arranged in order from the object side. Of a front lens group including a cemented lens in which a third lens, which is a negative lens directed to the side, and a fourth lens, which is a biconvex lens, are cemented together, a diaphragm, and an object side of a negative meniscus lens whose convex surface faces the image side. An optical system of four-group, five-lens structure including a rear group composed of a fifth lens, which is a hybrid lens having an optical resin thin film layer formed on its surface, and at least one of at least one lens in the front group. One surface is formed as an aspherical surface, and at least one surface including the surface of the optical resin thin film layer of the fifth lens is formed as an aspherical surface whose divergent action becomes weaker toward the periphery. Distance f, The focal length of the fifth lens f _5, the curvature radius or paraxial curvature radius of i-th lens surface or optical resin thin film layer surface counted from the object side R _i, the i-th lens surface or optical resin thin film from the object side When the axial distance from the layer surface is d _i and the refractive index of the _jth lens or optical resin thin film layer counted from the object side is n _j , (3) 0.8 f <| f ₅ | <1.2 f (4) 0.25 f <d ₇ + d ₈ <0.45 f It is characterized in that each conditional expression is satisfied.

[0007] The invention according to claim 3 provides the invention according to claim 1.
Alternatively, the invention described in 2 is characterized in that the entire optical system is configured to be extended to the object side at the time of short-distance photographing. Further, in the invention described in claim 4, in the invention described in claim 1 or 2, when the entire system of the optical system is extended to the object side and the short-distance photographing is performed, the extension speed of the rear group is extended to the front group. It is characterized in that it is configured so as to be delivered at a slower speed within a predetermined range than the speed.

[0008]

In the compact wide-angle lens constructed as described above, a telephoto type optical system configuration including a front group of a tesser type, an aperture stop, and a rear group of a negative meniscus lens having a convex surface facing the image side is adopted. ing. In order to reduce the telephoto ratio in this telephoto type wide-angle lens, it is necessary to increase the positive refractive power of the front lens group and the negative refractive power of the rear lens group, but in this case, the positive refractive power of the front lens group is increased. Is stronger,
Spherical aberration becomes under, and extroverted coma flare is likely to occur, field curvature becomes under, and distortion easily becomes positive (pincushion). On the other hand, if the negative refractive power of the rear group is increased, outward coma flare is likely to occur, and the distortion aberration tends to be positive (pincushion).

Therefore, in the present invention, in order to keep both the telephoto ratio small and correct various aberrations at the same time, conditional expression (1) is given to give the refraction effect of the first surface of the first lens. By properly defining the range, it is possible to reduce the telephoto ratio and prevent spherical aberration from becoming under. In addition, conditional expression (2) is given to properly define the range of the refracting action at the cemented surface of the cemented lens in the front group, thereby facilitating processing work such as polishing and making the fourth lens which is a convex lens easy. Higher order correction of spherical aberration and Petzval sum correction are performed while ensuring the edge thickness.

Further, given the conditional expression (3), the rear group (the fifth
By properly defining the range of the refractive power of the lens in relation to the refractive power of the entire system, coma flare and distortion,
The field curvature is well corrected and the telephoto ratio is prevented from increasing. Further, in order to achieve both the improvement of the optical performance and the downsizing of the optical system, conditional expression (4) is given, and the range of the sum of the air gaps sandwiching the diaphragm is appropriately defined, whereby the front group is emitted. The height at which the axial light flux and the peripheral light flux strike the rear group is properly maintained, and the desired back focus is maintained while preventing an increase in positive spherical aberration and an increase in the lens diameter of the fifth lens. Furthermore, by giving conditional expression (5) and properly defining the shape of the fifth lens, in particular, the field curvature becomes under, the occurrence of internal coma aberration, and the Petzval sum increase positively. It was designed to prevent this.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A small wide-angle lens according to claim 1 of the present invention is a first lens L ₁ which is a positive meniscus lens having a convex surface facing the object side, which is arranged in order from the object side. the second lens L ₂ is a biconcave lens, bonded bonded to the concave surface and the third lens L ₃ is a negative lens (biconcave lens) toward the image side and a fourth lens L ₄ is a biconvex lens L _{3 ·} a front group consisting of _4, a diaphragm S, an optical system with at configured 4-group 5-lens configuration rear group consisting of fifth lens L ₅ is a negative meniscus lens having a convex surface directed toward the image side, At least one surface of at least one lens in the front group is formed as an aspherical surface, and at least one surface of the fifth lens L ₅ is formed as an aspherical surface whose diverging action becomes weaker toward the periphery. F is the focal length of the entire system, and the focal length of the fifth lens L ₅ Is f ₅ , the curvature radius or paraxial curvature radius of the i-th lens surface counting from the object side is R _i , the axial distance between the i-th and i + 1-th surfaces counting from the object side is d _i , from the object side The refractive index of the j-th lens counted is n _j
And when (3) 0.8 f <| f ₅ | <1.2 f (4) 0.25 f <d ₇ + d ₈ <0.45 f It is configured to satisfy each of the following conditional expressions.

Generally, in a telephoto wide-angle lens composed of a front group of a tesser type, an aperture stop, and a rear group which is a negative meniscus lens having a convex surface facing the image side, in order to reduce the telephoto ratio, it is necessary to reduce the telephoto ratio. It is necessary to increase the positive refractive power and the negative refractive power of the rear group, respectively. However,
If the positive refractive power of the front group is increased, spherical aberration becomes under, and extroverted coma flare is likely to occur.
The field curvature is under, and the distortion is likely to be positive (pincushion).

Therefore, according to the invention of claim (1), in order to keep the telephoto ratio small and to correct various aberrations at the same time, the conditional expression (1) is given and the first surface R ₁ The range of refraction is defined. In this case, "R ₁ / (n ₁
-1.0) ”exceeds the lower limit of conditional expression (1), the telephoto ratio itself can be reduced, but spherical aberration occurs under, and when this is corrected with other parameters, higher-order terms Is likely to remain, and when the upper limit of conditional expression (1) is exceeded, it becomes impossible to reduce the telephoto ratio.

Further, in order to properly correct higher-order correction of spherical aberration and correction of Petzval sum, conditional expression (2) is given to properly set the range of refraction on the cemented surface R ₆ of the cemented lens L _3.4. Stipulated in. In this case, when the value of “R ₆ / (n ₄ −n ₃ )” exceeds the lower limit of the conditional expression (2), it is advantageous in correction, but the curvature of the joint surface R ₆ becomes tight and polishing or the like occurs. Processing becomes difficult, and if the edge thickness of the fourth lens L ₄ , which is a convex lens, is to be secured, the cemented lens L _3.4 becomes thick. Also, “R ₆ / (n ₄ −n ₃ )”
When the value of exceeds the upper limit of the conditional expression (2), the effect of providing the joint surface R ₆ becomes small.

On the other hand, when the negative refractive power of the rear group is increased in the telephoto type wide-angle lens described above, an outward coma flare is apt to occur, and the distortion is likely to be positive (pincushion). Therefore, in the invention of claim (1), the conditional expression (3) is given to satisfactorily correct the above-mentioned coma flare and distortion. This conditional expression (3) defines the range of the refractive power of the fifth lens L ₅ in relation to the refractive power of the entire system.

In this case, when the value of “| f ₅ |” exceeds the lower limit of the conditional expression (3), not only the curvature of field becomes excessive, but also the outward coma flare and the pincushion distortion aberration increase. . If the value of “| f ₅ |” exceeds the upper limit of the conditional expression (3), the effect of pushing the principal point toward the object side is reduced and the telephoto ratio becomes large.

Further, in the invention of claim (1), the conditional expression (4) is added in order to improve the optical performance and downsize the optical system. This conditional expression (4) defines the range of the sum “d ₇ + d ₈ ” of the air intervals that sandwich the diaphragm S.

In this case, if the value of "d ₇ + d ₈ " exceeds the lower limit of the conditional expression (4), the height of the on-axis light flux emitted from the front lens group, which strikes the rear lens group (the fifth lens L ₅ ) is high. Become. Therefore, not only the positive spherical aberration increases, but also the back focus cannot be reduced due to the strong divergence. Further, when the value of “| f ₅ |” exceeds the upper limit of the conditional expression (4), the fifth lens L of the peripheral luminous flux emitted from the front group is formed.
_The height that hits ₅ becomes high, and the lens diameter of the fifth lens L ₅ becomes large.

Conditional expression (5) defines the shape of the fifth lens L ₅ , and particularly relates to correction of field curvature. In this case, R ₈ becomes too loose | (R ₈ -R ₉ )
When the value of / (R ₈ + R ₉ ) | exceeds the lower limit of the conditional expression (5), the field curvature becomes under, inward coma occurs, and the Petzval sum tends to increase positively. Also, R
₈ is too strong _{| (R 8 -R 9) /} (R 8 + R 9)
When the value of | exceeds the upper limit of the conditional expression (5), an aberration opposite to the aberration that occurs when the lower limit is exceeded will occur.

The compact wide-angle lens described in claim 2 of the present invention is, as shown in FIG. 2, a first lens which is a positive meniscus lens with convex surfaces facing the object side, which are arranged in order from the object side. From L ₁ , the second lens L ₂ which is a biconcave lens, and the cemented lens L _{3 and 4} in which the third lens L ₃ which is a negative lens with the concave surface facing the image side and the fourth lens ₄ which is a biconvex lens are bonded together. And a rear group including a stop S and a fifth lens L ₅ ′, which is a hybrid lens in which an optical resin thin film layer is formed on the object-side surface of a negative meniscus lens having a convex surface facing the image side. In the optical system of 5 elements in 4 groups, at least one surface of at least one lens in the front group is formed as an aspherical surface, and includes the surface of the optical resin thin film layer of the fifth lens L ₅ ′. At least one surface has a weaker divergence toward the periphery It becomes formed as aspheric, further the focal length of the entire system f, and the focal length f ₅ of the fifth lens L ₅ ', as counted from the object side of the i-th lens surface or optical resin thin film layer surface of curvature radius or near The axial radius of curvature is R _i , the axial distance between the i-th and the (i + 1) th lens surface or the optical resin thin film layer surface counted from the object side is d _i , and the j-th lens or the optical resin thin film layer refraction counted from the object side is refracted. When the rate is n _j , (3) 0.8 f <| f ₅ | <1.2 f (4) 0.25 f <d ₇ + d ₈ <0.45 f It is configured to satisfy each of the following conditional expressions.

According to the invention of claim 2, the fifth lens L ₅ '
Each lens L except that is a hybrid lens
Arrangement of _{1 to} L ₅ and assigned conditional expressions (1) to (4)
Is configured similarly to the case of the invention of claim 1. Therefore, the reasons for the existence of the conditional expressions (1) to (4) and the phenomena when the lower and upper limits of these conditional expressions are exceeded are the same as in the case of the invention of claim 1. The reason why the fifth lens L ₅ ′ is formed as a hybrid lens is based on the following reason.

[0022] That is, the conditional expression according to claim 2 (Any claim 1 equivalent) (3) and (5) a non-spherical lens L ₅ is defined by the '(L ₅ in claim 1), if the tight meniscus I have no choice. However, when the meniscus lens having such a shape is processed by the glass molding method,
Since the releasability at the time of processing is deteriorated and the yield at the time of manufacturing is not improved, there arises a problem that the difficulty in the manufacturing process increases. In order to eliminate this, the lens itself made of glass material is previously formed as a spherical lens,
An optical resin thin film layer whose surface becomes a required aspherical surface may be formed on a spherical surface which should be an aspherical surface of this spherical lens, that is, as a hybrid lens.
In the invention of claim 2, for this reason, the fifth lens L is
₅ 'is obtained by forming as a hybrid lens.

In this case, R ₈ becomes loose, and | (R ₈ −
If the value of R ₁₀ ) / (R ₈ + R ₁₀ ) | exceeds the lower limit of conditional expression (5) and becomes too loose, the curvature of field becomes under, inward coma aberration occurs, and Petzval sum becomes makes it easier just to increase, also, R ₈ is too strong, | (R ₈
If the value of −R ₁₀ ) / (R ₈ + R ₁₀ ) | exceeds the upper limit of conditional expression (5) and becomes too strong, an aberration opposite to the aberration that occurs when the lower limit is exceeded will not occur. The same as the case of the invention of claim 1.

According to a third aspect of the present invention, the small wide-angle lens is constructed so as to extend the entire optical system to the object side during short-distance photography. In the telephoto type photographing optical system, it is usual to employ a method of moving only the front group toward the object side at the time of short-distance photographing. This is because the lens barrel mechanism including the payout mechanism is simplified, and the payout amount is small. However, this method can be applied to a wide-angle lens having specifications (F _No. , angle of view) of a conventional level, but in a large-diameter, wide-angle, high-performance photographic optical system like the present invention, In order to enable short-distance shooting at a magnification of about 1/10, only the front group or only the rear group moves (extends)
It is difficult to maintain high performance. Therefore, the invention of claim 3 is configured such that the entire optical system is extended to the object side during short-distance shooting.

In the compact wide-angle lens according to claim 4 of the present invention, when the entire optical system is extended to the object side, the moving speed of the rear group is slower than the moving speed of the front group within a predetermined range. It is configured to pay off at speed. As described above, in the case of adopting the system in which the entire optical system is extended to the object side during short-distance shooting, the height of the peripheral luminous flux emitted from the front group and striking the rear group becomes small.
As a result, the effect of correcting the field curvature of the rear group is reduced, and the image surface becomes under.

As a method of correcting this, the axial distance between the front group and the rear group at the time of extension is widened so that the height of the peripheral luminous flux emitted from the front group and hitting the rear group is returned to an appropriate height. That method is possible.

In this case, when the extension amount of the front group is M _f and the extension amount of the rear group is M _r , both groups are set so as to satisfy the conditional expression (6) 0.7 <M _r / M _f <1.0. It has been found that if the lens is moved, the fluctuation of the performance can be suppressed to be small, and high performance can be obtained over the entire target shooting distance. According to the fourth aspect of the invention, based on such a result, the moving speed of the rear group is set to be slower within a predetermined range than the moving speed of the front group.

[0028]

EXAMPLES Specific examples of the small wide-angle lens according to the present invention will be described below, but Examples 1 to 5 are examples corresponding to the invention of claim 1, and all of them are examples. The optical system configuration shown in FIG. 1 is provided, while the sixth embodiment is an example corresponding to the invention of claim 2 and has the optical system configuration shown in FIG. The symbols used in the data tables of each example have the following meanings. f: focal length of the entire system T _r : telephoto ratio F _{No .} : F number ω: half angle of view No .: surface or aperture number R _i : radius of curvature of the ith lens surface counted from the object side or paraxial Radius of curvature d _i : On-axis spacing between the i-th surface and the (i + 1) th surface counted from the object side n _j : Refractive index of the j-th lens counted from the object side ν _j : Of the j-th lens counted from the object side Abbe number Further, the aspherical surface used in the small wide-angle lens (Examples 1 to 6) of the present invention has a conic constant of k, and aspherical coefficients of the _4th to 10th orders are A _{4 to} A ₁₀ . Then, it is expressed by the following aspherical expression.

[0029]

[Equation 1]

[0030]

Table 1 <Example 1> f = 28.8 T _r = 1.04 F _No. = 2.88 ω = 36.2 ° Conditional expression (1) = 0.53f Conditional expression (2) = 3.10f Conditional expression (3) = 0.97f Conditional expression (4) = 0.36f Conditional expression (5) = 0.30

[0031]

Table 2 <Example 2> f = 28.8 T _r = 1.07 F _No. = 2.88 ω = 36.2 ° Conditional expression (1) = 0.62f Conditional expression (2) = 1.96f Conditional expression (3) = 1.10f Conditional expression (4) = 0.36f Conditional expression (5) = 0.24

[0032]

Table 3 <Example 3> f = 28.8 T _r = 1.09 F _No. = 2.9 ω = 36.3 ° Conditional expression (1) = 0.70f Conditional expression (2) = 1.67f Conditional expression (3) = 0.94f Conditional expression (4) = 0.32f Conditional expression (5) = 0.29

[0033]

[Table 4] <Example 4> f = 28.8 T _r = 1.09 F _No. = 2.88 ω = 36.2 ° Conditional expression (1) = 0.78f Conditional expression (2) = 2.16f Conditional expression (3) = 0.91f Conditional expression (4) = 0.38f Conditional expression (5) = 0.33

[0034]

Table 5 <Example 5> f = 28.2 T _r = 1.03 F _No. = 2.88 ω = 36.8 ° Conditional expression (1) = 0.50f Conditional expression (2) = 7.13f Conditional expression (3) = 0.88f Conditional expression (4) = 0.35f Conditional expression (5) = 0.32

[0035]

Table 6 <Example 6> f = 28.4 T _r = 1.06 F _No. = 2.88 ω = 36.6 ° Conditional expression (1) = 0.59f Conditional expression (2) = 2.41f Conditional expression (3) = 0.86f Conditional expression (4) = 0.37f Conditional expression (5) = 0.26 Next, Example 1 to 6 show spherical aberrations (including a sine condition), astigmatism, distortion, coma in the meridional direction and the coma in the sagittal direction related to the small wide-angle lens of FIGS.
As shown in FIGS. 8A and 8B, as can be clearly seen from the respective aberration diagrams, all of the small wide-angle lenses according to the present invention have FN
o. is as bright as 2.8, and the half angle of view is 36.2 ° to 36.8.
Despite the high performance of °, each aberration is well corrected. It can be said that the small wide-angle lens of the present invention is an excellent optical system as compared with the conventional wide-angle photographing optical system.

The above description is based on the six embodiments shown in the drawings, but the present invention is not limited to this, and various modifications can be made without departing from the scope of the invention. For example, in Example 6, the object side surface (concave surface) of the fifth lens is formed as the optical resin thin film layer surface, but it goes without saying that it is also possible to form the optical resin thin film layer on the image side surface (convex surface). Nor. In the illustrated embodiment, the LSC photographing lens has been described, but it can be sufficiently used as, for example, a camcorder photographing lens, an SVC photographing lens, and a reading lens.

[0037]

As described above, the compact wide-angle lens of the present invention has a telephoto ratio of about 1.0, an F _No. of 2.8 class, and a compact and large aperture with an angle of view exceeding 72 °. Although each lens has good performance, each aberration is satisfactorily corrected, and its high performance can be maintained even when the shooting distance changes, resulting in excellent effects not seen with conventional wide-angle lenses. Can be said. Further, when the present invention is configured as in claim 2, in addition to the above-mentioned effect, a highly practical effect of obtaining a small wide-angle lens excellent in mass productivity can be obtained.

[Brief description of drawings]

FIG. 1 is a first to fifth example of a small wide-angle lens according to the present invention.
FIG. 3 is a configuration diagram of an optical system of FIG.

FIG. 2 is a configuration diagram of an optical system of Example 6 relating to a small wide-angle lens of the present invention.

FIG. 3 is an aberration diagram showing spherical aberration (including a sine condition), astigmatism, distortion, and coma in the meridional direction and the sagittal direction of the small wide-angle lens according to the first example of the present invention. The symbol SA in the spherical aberration diagram is the symbol of the spherical aberration.
SC shows a diagram of the sine condition line, symbol DM in the astigmatism diagram shows a diagram in the meridional direction, and symbol DS shows a diagram in the sagittal direction (in this spherical aberration diagram, respectively). And the description of each symbol in the astigmatism diagram is common to each of the aberration diagrams shown below).

FIG. 4 is an aberration diagram showing spherical aberration (including a sine condition), astigmatism, distortion, and coma in the meridional direction and the sagittal direction of a small wide-angle lens according to Example 2 of the present invention.

FIG. 5 is an aberration diagram showing spherical aberration (including a sine condition), astigmatism, distortion, and coma in the meridional direction and the sagittal direction of a small wide-angle lens according to Example 3 of the present invention.

FIG. 6 is an aberration diagram showing spherical aberration (including a sine condition), astigmatism, distortion, and coma in the meridional direction and the sagittal direction of a small wide-angle lens according to Example 4 of the present invention.

FIG. 7 is an aberration diagram showing spherical aberration (including a sine condition), astigmatism, distortion, and coma in the meridional direction and the sagittal direction of a small wide-angle lens according to Example 5 of the present invention.

FIG. 8 is an aberration diagram showing spherical aberration (including a sine condition), astigmatism, distortion, and coma in the meridional direction and the sagittal direction of a small wide-angle lens according to Example 6 of the present invention.

[Explanation of symbols]

d ₁ , d ₂ ... d ₁₁ Lens thickness or air space on the optical axis L ₁ First lens L ₂ Second lens L ₃ Third lens L ₄ Fourth lens L ₅ , L ₅ ′ Fifth lens R ₁ , R ₂ ... curvature radius S diaphragm R ₁₀ lens surface

Claims (4)

[Claims] 1. A first lens which is a positive meniscus lens having a convex surface facing the object side, a second lens which is a biconcave lens, and a negative lens whose concave surface faces the image side, which are arranged in order from the object side. It is composed of a front group consisting of a cemented lens in which three lenses and a fourth lens which is a biconvex lens are cemented together, an aperture stop, and a rear group consisting of a fifth lens which is a negative meniscus lens with its convex surface facing the image side. Further, in the optical system of 4 groups 5 elements, at least one surface of at least one lens in the front group is formed as an aspherical surface, and at least one surface of the fifth lens becomes closer to the periphery. It is formed as an aspherical surface that weakens the divergence action, and the focal length of the entire system is f, the focal length of the fifth lens is f ₅ , and the radius of curvature of the i-th lens surface counted from the object side or the paraxial radius of curvature is R _i, counted from the object side Th and i
The axial distance from the + 1st surface is d _i , and j is counted from the object side.
When the refractive index of the th lens is n _j , (3) 0.8 f <| f ₅ | <1.2 f (4) 0.25 f <d ₇ + d ₈ <0.45 f A small wide-angle lens characterized by satisfying each of the following conditional expressions. 2. A first lens which is a positive meniscus lens having a convex surface facing the object side, a second lens which is a biconcave lens, and a negative lens whose concave surface faces the image side, which are arranged in order from the object side. An optical resin thin film layer is formed on the object side surface of a negative meniscus lens whose convex surface is directed toward the image side, a front group including a cemented lens in which three lenses and a fourth lens which is a biconvex lens are bonded together. 5th which is a hybrid lens
An optical system of a four-group, five-element configuration including a rear group of lenses, wherein at least one surface of at least one lens in the front group is formed as an aspherical surface, and the fifth lens includes At least one surface including the surface of the optical resin thin film layer is formed as an aspherical surface having a divergent action weakening toward the periphery, and the focal length of the entire system is f, the focal length of the fifth lens is f ₅ , and the object is The radius of curvature or paraxial radius of curvature of the i-th lens surface or the optical resin thin film layer surface counted from the side is R _i , the axial distance from the i-th lens surface or the optical resin thin film layer surface counted from the object side is d _i , When the refractive index of the j-th lens or the optical resin thin film layer counted from the object side is n _j , (3) 0.8 f <| f ₅ | <1.2 f (4) 0.25 f <d ₇ + d ₈ <0.45 f A small wide-angle lens characterized by satisfying each of the following conditional expressions. 3. The small wide-angle lens according to claim 1, wherein the entire optical system is extended toward the object side when taking a close-up image. 4. When the entire optical system is extended to the object side and short-distance photographing is performed, the rear group is extended at a slower speed within a predetermined range than the front group is extended. The compact wide-angle lens according to claim 3.