JPH0611649A - Lens for optical recording - Google Patents

Abstract

PURPOSE:To assure a working distance and to well correct aberrations including curvature of field and axial chromatic aberration by constituting the above lens of specific 5 groups and satisfying specific conditions. CONSTITUTION:This lens is constituted of the 5 groups; the 1st lens group consisting of a positive single lens, the convex face of which is directed to the object side, the 2nd lens group consisting of a negative single lens, the concave face of which is directed to the object side, the positive 3rd lens group, the 4th lens group, the convex face of which is directed to the object side, and the 5th lens group which is a positive meniscus single lens, the convex face of which is directed to the object side. The above-mentioned lens satisfies the conditions expressed by equations. In the equations, (f) is the focal length of the entire system, fa is the combined focal length of the 1st and 2nd lens groups, d4 is the spacing on the optical axis of the 2nd and 3rd lens groups, d3 is the thickness on the optical axis of the 2nd lens group, n2 is the refractive index of the 2nd lens group, r3 is the radius curvature of the object side of the 2nd lens group, r4 is the radius of curvature of the image side face of the 2nd lens group.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical recording lens suitable for an optical system of a system for recording information on an optical information recording medium such as a magneto-optical disk or a magneto-optical tape or reproducing the recorded information. In particular, it relates to an optical recording lens of a type that corrects aberrations by combining a plurality of lenses.

[0002]

2. Description of the Related Art In recent years, a lens having a single-sided aspherical surface has been used as a lens for an optical disk.
However, it is difficult to correct field curvature and axial chromatic aberration with an aspherical single lens.

Among lenses constructed by combining a plurality of lenses, the lens type having a relatively large image circle is disclosed in Japanese Patent Publication No. 58-1762 and Japanese Patent Publication No. 62-16.
Those described in JP-A No. 411, JP-A-57-104914, JP-B-63-3284, JP-A-62-98317, and JP-A-62-217214 are known.

[0004]

However, the lenses described in the above-mentioned respective publications are designed as an objective lens for converging a single light beam on the recording surface and have a large aperture, but the image plane is large. It has the problems of large curvature and short working distance.

In order to increase the speed of recording / reproducing, a multi-beam method which enables parallel recording or parallel reading by a plurality of light beams is effective. However, in a multi-beam optical system, when the lens has a field curvature, the focal position of each beam varies. In the case of a single beam, the focus shift can be canceled by the autofocus mechanism, but in the case where there are variations in the focus positions of the multiple beams, it cannot be canceled by the autofocus mechanism. Therefore, when adopting the multi-beam method, a lens having good off-axis performance including field curvature is required.

In particular, in a system in which an objective lens is fixedly provided on an optical head that moves in the radial direction of an optical disk and a movable lens for focusing and tracking is provided outside the optical head, a lens that makes light enter the movable lens. , Or the number of lens elements is increased in order to provide a lens or the like for collimating the light emitted from the movable lens, and thus the undercorrected field curvature of the lens elements is accumulated and the field curvature is increased. There is a tendency.

Therefore, when the multi-beam method is adopted, it is necessary to reduce the field curvature as much as possible in the other lenses including the movable lens. Further, in the movable lens and the lens in the vicinity thereof, it is necessary to secure a large working distance for disposing the lens actuator.

A semiconductor laser is promising as a light source of the multi-beam system, but since the oscillation wavelength of the semiconductor laser changes with the output change and defocus occurs, in a recordable system using the semiconductor laser,
In order to prevent the influence, it is necessary to suppress the axial chromatic aberration sufficiently small.

[0009]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems of the prior art, and is an optical recording in which the working distance is secured and the aberrations including the field curvature and the axial chromatic aberration are well corrected. A lens for use is provided.

[0010]

In order to achieve the above object, an optical recording lens according to the present invention has a first lens group consisting of a positive single lens having a convex surface facing the object side and a concave surface facing the object side. , A second lens group consisting of a negative single lens, a positive third lens group, a positive fourth lens group with a convex surface facing the object side, and a positive meniscus single lens with a convex surface facing the object side. It is characterized in that it is made up of five groups, namely, a fifth lens group, and satisfies the following conditions.

[0011]

[Equation 1] -0.47 <f / fa <-0.20 (1) 0.4 <(d4 + d3 / n2) / f <1.2 (2) -1.2 <(r3 + r4) / (r3-r4) <-0.4 (3) Where f is the focal length of the entire system, fa is the combined focal length of the first and second lens groups, d4 is the distance between the optical axes of the second and third lens groups, and d3 is the thickness of the optical axis of the second lens group. Here, n2 is the refractive index of the second lens group, r3 is the radius of curvature of the object side surface of the second lens group, and r4 is the radius of curvature of the image side surface of the second lens group.

[0012]

Embodiments of the present invention will be described below.

The optical recording lens of the embodiment is composed of five groups of positive, negative, positive, positive and positive from the object side.
(1) (2) (3) is satisfied.

In order to secure the working distance, it is necessary to increase the height of incidence of the marginal ray on the final lens. In the lens of the four-group, four-element configuration as described in Japanese Unexamined Patent Publication No. 62-217214, the power up to the second lens is made negative to diverge the light beam, and the distance between the second lens and the third lens is set to be small. By widening it, the height of incidence on the third lens can be increased.

However, if the degree of divergence of the light beam incident on the third lens is too strong in the fourth group consisting of four lenses, the positive power borne by the third and fourth lenses becomes excessive, and it becomes difficult to correct spherical aberration. .

Therefore, the lens of the present invention has
To prevent the power of the positive lens of one sheet from becoming excessive, another positive lens group is arranged between the negative second lens group and the two positive lens groups on the light-collecting side, and positive, negative, positive, positive , And has a positive five-group configuration, and the light incident on the fourth lens group is set to be a substantially parallel light flux.

With the five-group structure, the negative power of the second lens group can be set relatively strong, so that the astigmatic difference can be easily corrected. Further, since the height of incident light rays on the lenses after the third lens group is high, the power of each lens can be made small, and the Petzval sum can be made smaller than the type of four groups and four lenses to easily correct the field curvature.

The expressions (1) and (2) define the degree of divergence of the luminous flux after the second lens group is emitted and the distance to the third lens group, and the marginal distance to the third lens group is determined by these factors. This is a condition for securing the incident height of the light beam. A working distance can be secured by satisfying this condition.

When the value goes below the lower limit of the expression (1), the divergence of the light beam emitted from the second lens group becomes excessive and high-order aberrations occur, which makes it difficult to make a bright lens. If the upper limit is exceeded, the divergence of the luminous flux will be too weak, and the lens spacing will be large and the overall length will be long in order to secure the incident height of the marginal ray. If the lens spacing is shortened, it will not be possible to secure a sufficient working distance. .

When the value goes below the lower limit of the expression (2), the distance between the second and third lens groups is too narrow, it becomes difficult to correct the astigmatic difference, and the working distance becomes short. If the upper limit is exceeded, the astigmatic difference will be overcorrected and the total lens length will be increased.

Expression (3) is a condition indicating the shape of the second lens group, and sets the aberration burden balance on the front and rear surfaces of the second lens group. If the value is below the lower limit, the second lens group has a meniscus shape with a concave surface facing the object side, the astigmatic difference correction amount on the exit side surface is insufficient, and the best off-axis image surface is below the Petzval image surface. . If the upper limit is exceeded, the negative power is distributed unevenly to the exit side surface, and the spherical aberration correction amount on the entrance side surface becomes insufficient.

The optical recording lenses of the respective examples described later satisfy the following conditional expressions (4), (5) and (6).

[0023]

N2> 1.60 (4) n4> 1.65 (5) n5> 1.70 (6) where n3 is the refractive index of the lens forming the third lens group, and n4 is the refraction of the lens forming the fourth lens group. Rate, n5
Is the refractive index of the lenses constituting the fifth lens group.

Equations (4), (5) and (6) are conditions that indicate the selection of the glass material of the positive lens group. To correct the field curvature,
It is necessary to bring the Petzval sum close to 0, and for that purpose, glass materials having a high refractive index must be used for many positive lenses. When the value is below the lower limit of each equation, the field curvature is insufficiently corrected and a wide image circle cannot be secured. Since the third lens group has a great influence on chromatic aberration, its refractive index is a value slightly lower than that of the other lens groups in order to balance field curvature and chromatic aberration correction described later.

On the other hand, in particular, the refractive index of the fifth lens group expressed by the equation (6) not only affects the curvature of field, but also corrects spherical aberration and coma in a well-balanced manner depending on the shape of the fifth lens group. Therefore, it is necessary to set it high.

It should be noted that these conditions (4), (5) and (6) do not necessarily have to be satisfied if correction of only the astigmatic difference of the optical recording lens becomes a problem.

The optical recording lens of Example 3-10 is the third type.
The lens group or the fourth lens group is a positive and negative cemented lens. This is because if all the five lens groups are composed of a single lens, the field curvature and the chromatic aberration cannot be corrected in a well-balanced manner. That is, the field curvature and the chromatic aberration are determined by the balance of the power, dispersion, refractive index, etc. of the positive lens and the negative lens, but the amount generated in the positive lens group with a large number is reduced and a single negative lens is used. It is possible to achieve balance by increasing the amount generated in the lens group.

However, when a glass material having a high refractive index is used for the positive lens in order to reduce the Petzval sum for the purpose of correcting the field curvature, there is no glass material having a large Abbe number in the high refractive index. However, the dispersion of the positive lens becomes large, the chromatic aberration of the positive lens cannot be canceled by the single negative lens, and it becomes difficult to correct the chromatic aberration. Also,
When a glass material having a large dispersion is used for the negative second lens group for correction of chromatic aberration, the refractive index of the glass material becomes high, so that the negative Petzval sum becomes small and the field curvature is insufficiently corrected.

In order to balance the aberrations, it is desirable that a lens group having a high incident height of marginal rays is a cemented lens. When correcting the axial chromatic aberration in the near-infrared region with the fifth-group lens according to the present invention, the first, second,
The chromatic aberration cannot be sufficiently corrected even if only one of the three lens groups of the fifth lens group is cemented.

Therefore, in the optical recording lens of Example 3-10, the third lens group or the fourth lens group is cemented with positive and negative lenses, and the negative lens and the second lens group of the cemented lens are negative lenses. The chromatic aberration and the field curvature are corrected in a well-balanced manner by sharing the function of.

When the third lens group or the fourth lens group is constructed as a positive and negative cemented lens to correct chromatic aberration, if the negative lens is selected with a lower refractive index than the positive lens, the cemented lens will be underexposed. Spherical aberration occurs and the negative spherical aberration correction capability of the second lens group makes it impossible to correct the aberration of the entire system, and since there is no high-dispersion glass material with a low refractive index, the chromatic aberration correction capability is also low. Therefore, it is desirable to select a negative lens that also satisfies the above conditions (4) and (5).

In the optical recording lenses of Examples 3 and 4, the third lens group is constructed by laminating a negative third lens and a biconvex positive fourth lens in order from the object side, and the following conditions are satisfied. Meet

[0033]

(3) νdp / νdn> 1.6 (7) 0.80 <rC / f <1.4 (8) where νdp is the Abbe number of the positive lens that constitutes the cemented lens, and νdn is the Abbe of the negative lens that constitutes the cemented lens. The number and rC are the radii of curvature of the bonding surfaces.

The optical recording lenses of Examples 5 and 6 are
The third lens group is configured by laminating a positive third lens and a negative meniscus fourth lens having a concave surface facing the object side in order from the object side, and the following conditions are satisfied.

[0035]

[Equation 4] νdp / νdn> 1.6 (9) -0.90 <rC / f <-0.50 (10)

In the optical recording lenses of Examples 7 and 8, the fourth lens unit is constructed by bonding a fourth lens having a negative meniscus with a convex surface facing the object side in order from the object side and a fifth lens having a positive refractive power. The following conditions are met.

[0037]

[Equation 5] νdp / νdn> 1.6 (11) 0.55 <rC / f <1.0 (12)

The optical recording lenses of Examples 9 and 10 were the fourth type.
The lens group is configured by bonding a biconvex positive fourth lens and a negative fifth lens in order from the object side, and satisfies the following conditions.

[0039]

[Equation 6] νdp / νdn> 1.6 (13) -1.4 <rC / f <-0.72 (14)

The expressions (7), (9), (11) and (13) define the lower limit of the ratio of Abbe numbers of positive and negative lenses. Below the lower limit, chromatic aberration cannot be sufficiently corrected unless the curvature of the bonding surface is increased, and in that case, a bright lens having a large NA cannot be constructed.

Expressions (8), (10), (12) and (14) define the radius of curvature of the bonding surface. If the curvature becomes too tight beyond the limit where the absolute value of the numerical value is small, it is difficult to secure the edge of the lens, and the amount of change in spherical aberration with respect to wavelength change becomes too large. If the absolute value of the numerical value exceeds the limit on the large side, chromatic aberration cannot be sufficiently corrected.

When the difference in refractive index between the positive and negative lenses of the cemented lens is large, spherical aberration occurs when rC that allows sufficient color correction is selected if the refractive index of the positive lens is high, and the negative lens refraction If the index is high, the field curvature will be undercorrected, so it is desirable to use a combination that satisfies Expression (15) and has a small difference in refractive index.

[0043]

[Equation 7] -0.1 <np-nn <0.1 (15) where np is the refractive index of the positive lens of the cemented lens,
nn is the refractive index of the negative lens of the cemented lens.

[0044]

[Embodiment 1] FIG. 1 shows Embodiment 1 of the present invention. The specific numerical structure is shown in Table 1. N in the table
A is the numerical aperture, f is the focal length at 780 nm, ω is the half angle of view, f
B is the back focus, r is the radius of curvature, d is the lens thickness or the air gap, nd is the refractive index at d-line (588 nm), ν is the Abbe number, and n780 is the refractive index at the wavelength of 780 nm.

FIG. 2 shows spherical aberration SA, sine condition SC, wavelength 750.
It shows chromatic aberration, astigmatism (S: sagittal, M: meridional), and distortion that are indicated by spherical aberration at nm, 780 nm, and 810 nm.

[0046]

[Table 1] NA = 0.40 f = 1.00 ω = 2.0 ° fB = 0.90 Surface number rd nd ν n780 1 2.709 0.206 1.88300 40.8 1.86888 2 19.141 0.076 3 -1.117 0.180 1.62004 36.3 1.60910 4 5.407 0.720 5 -7.713 0.249 1.88300 40.8 1.86888 6 -1.678 0.014 7 2.233 0.232 1.88300 40.8 1.86888 8 16.572 0.014 9 0.952 0.318 1.88300 40.8 1.86888 10 1.114

[0047]

Second Embodiment FIG. 3 shows a second embodiment of the present invention. The specific numerical structure is shown in Table 2. 11th
The surface and the twelfth surface correspond to the cover glass attached to the light source. FIG. 4 shows various aberrations of the lens of this example.

[0048]

[Table 2] NA = 0.37 f = 1.00 ω = 2.0 ° fB = 0.90 Surface number rd nd ν n780 1 2.911 0.205 1.77250 49.6 1.76203 2 -18.303 0.066 3 -1.124 0.207 1.62004 36.3 1.60910 4 5.593 0.687 5 -6.400 0.250 1.77250 49.6 1.76203 6 -1.539 0.014 7 2.276 0.234 1.77250 49.6 1.76203 8 68.928 0.014 9 0.969 0.314 1.88300 40.8 1.86888 10 1.257 0.873 11 ∞ 0.040 1.51633 64.1 1.51072 12 ∞

[0049]

[Third Embodiment] FIG. 5 shows a third embodiment of the present invention. The specific numerical structure is shown in Table 3. Figure 6
The various aberrations of the lens of this example are shown.

[0050]

[Table 3] NA = 0.40 f = 1.00 ω = 2.0 ° fB = 0.90 Surface number rd nd ν n780 1 2.171 0.218 1.61800 63.4 1.61139 2 -7.704 0.054 3 -1.240 0.180 1.84666 23.8 1.82484 4 157.050 0.493 5 -11.184 0.198 1.84666 23.8 1.82484 6 1.080 0.338 1.83481 42.7 1.82195 7 -1.843 0.014 8 2.284 0.216 1.77250 49.6 1.76203 9 -30.090 0.014 10 1.013 0.270 1.88300 40.8 1.86888 11 1.350

[0051]

Fourth Embodiment FIG. 7 shows a fourth embodiment of the present invention. The specific numerical structure is shown in Table 4. Figure 8
The various aberrations of the lens of this example are shown.

[0052]

[Table 4] NA = 0.37 f = 1.00 ω = 2.0 ° fB = 0.90 Surface number rd nd ν n780 1 2.574 0.211 1.77250 49.6 1.76203 2 -14.406 0.063 3 -1.359 0.386 1.75000 25.1 1.73166 4 3.915 0.593 5 -90.000 0.180 1.75000 25.1 1.73166 6 1.050 0.388 1.74100 52.6 1.73145 7 -1.908 0.013 8 2.300 0.229 1.80400 46.6 1.79251 9 -40.700 0.013 10 1.012 0.464 1.80400 46.6 1.79251 11 1.135 0.781 12 ∞ 0.040 1.51633 64.1 1.51072 13 ∞

[0053]

[Fifth Embodiment] FIG. 9 shows a fifth embodiment of the present invention. The specific numerical structure is shown in Table 5. Figure 10
Shows various aberrations of the lens of this example.

[0054]

[Table 5] NA = 0.40 f = 1.00 ω = 2.0 ° fB = 0.90 Surface number rd nd ν ν n780 1 3.273 0.285 1.80400 46.6 1.79251 2 -8.233 0.054 3 -1.300 0.540 1.75000 25.1 1.73166 4 6.014 0.480 5 24.677 0.360 1.83481 42.7 1.82195 6 -0.642 0.198 1.84666 23.8 1.82484 7 -2.124 0.016 8 1.975 0.216 1.77250 49.6 1.76203 9 169.714 0.016 10 0.954 0.270 1.88300 40.8 1.86888 11 1.091

[0055]

Sixth Embodiment FIG. 11 shows a sixth embodiment of the present invention. The specific numerical structure is shown in Table 6. Figure 12
Shows various aberrations of the lens of this example.

[0056]

[Table 6] NA = 0.40 f = 1.00 ω = 2.0 ° fB = 0.72 Surface number rd nd ν ν n780 1 2.432 0.497 1.77250 49.6 1.76203 2 -7.255 0.054 3 -1.390 0.475 1.84666 23.8 1.82484 4 4.693 0.406 5 10.578 0.338 1.72916 54.7 1.72007 6 -0.735 0.198 1.75000 25.1 1.73166 7 -1.776 0.154 8 1.751 0.216 1.77250 49.6 1.76203 9 48.607 0.014 10 0.782 0.270 1.83481 42.7 1.82195 11 0.849

[0057]

Seventh Embodiment FIG. 13 shows a seventh embodiment of the present invention. The specific numerical structure is shown in Table 7. Figure 14
Shows various aberrations of the lens of this example.

[0058]

[Table 7] NA = 0.37 f = 1.00 ω = 2.0 ° fB = 0.90 Surface number rd nd ν n780 1 3.065 0.198 1.77250 49.6 1.76203 2 -8.010 0.067 3 -1.095 0.203 1.75000 25.1 1.73166 4 9.789 0.533 5 -5.475 0.230 1.67000 57.3 1.66205 6 -1.341 0.014 7 2.482 0.198 1.75000 25.1 1.73166 8 0.762 0.342 1.74100 52.6 1.73145 9 -17.616 0.014 10 0.981 0.243 1.88300 40.8 1.86888 11 1.598

[0059]

[Eighth Embodiment] FIG. 15 shows an eighth embodiment of the present invention. The specific numerical structure is shown in Table 8. Fig. 16
Shows various aberrations of the lens of this example.

[0060]

[Table 8] NA = 0.37 f = 1.00 ω = 2.0 ° fB = 0.90 Surface number rd nd ν n780 1 3.149 0.198 1.77250 49.6 1.76203 2 -17.938 0.067 3 -1.034 0.180 1.75000 25.1 1.73166 4 -69.302 0.522 5 -6.059 0.230 1.77250 49.6 1.76203 6 -1.457 0.014 7 2.643 0.198 1.84666 23.8 1.82484 8 0.677 0.342 1.83481 42.7 1.82195 9 -20.531 0.014 10 0.974 0.243 1.88300 40.8 1.86888 11 1.439

[0061]

[Ninth Embodiment] FIG. 17 shows a ninth embodiment of the present invention. The specific numerical structure is shown in Table 9. Figure 18
Shows various aberrations of the lens of this example.

[0062]

[Table 9] NA = 0.37 f = 1.00 ω = 2.0 ° fB = 0.89 Surface number rd nd ν n780 1 3.213 0.200 1.77250 49.6 1.76203 2 -17.151 0.067 3 -1.025 0.180 1.75000 25.1 1.73166 4 -89.545 0.522 5 -6.684 0.216 1.77250 49.6 1.76203 6 -1.454 0.014 7 2.742 0.338 1.83481 42.7 1.82195 8 -0.900 0.198 1.84666 23.8 1.82484 9 -21.251 0.014 10 0.990 0.270 1.88300 40.8 1.86888 11 1.473

[0063]

Tenth Embodiment FIG. 19 shows a tenth embodiment of the present invention. The specific numerical structure is shown in Table 10. Figure
20 indicates various aberrations of the lens of this example.

[0064]

[Table 10] NA = 0.37 f = 1.00 ω = 2.0 ° fB = 0.88 Surface number rd nd ν n780 1 2.487 0.218 1.61800 63.4 1.61139 2 -8.072 0.059 3 -1.094 0.180 1.84666 23.8 1.82484 4 -81.137 0.525 5 -7.238 0.216 1.77250 49.6 1.76203 6 -1.506 0.014 7 2.742 0.338 1.83481 42.7 1.82195 8 -1.102 0.198 1.84666 23.8 1.82484 9 -16.920 0.014 10 1.025 0.270 1.88300 40.8 1.86888 11 1.607

Tables 11 and 12 show the correspondence between the above-mentioned conditional expressions and the respective embodiments.

[0066]

[Table 11] Example 1 2 3 4 5 (1) -0.347 -0.319 -0.274 -0.343 -0.319 Article (2) 0.832 0.816 0.592 0.815 0.792 (3) -0.657 -0.665 -0.984 -0.485 -0.644 (4 ) 1.868 1.762 1.824 1.731 1.821 1.821 1.731 1.824 formula (5) 1.868 1.762 1.762 1.792 1.762 (6) 1.868 1.868 1.868 1.792 1.868 (7) (9) (11) (13) 1.79 2.10 1.79 (8) (10) (12) (14) 1.08 1.05 -0.64

[0067]

[Table 12] Example 6 7 8 9 10 (1) -0.281 -0.306 -0.381 -0.393 -0.386 Article (2) 0.666 0.650 0.625 0.625 0.623 (3) -0.543 -0.798 -1.030 -1.023 -1.027 (4 ) 1.720 1.662 1.762 1.762 1.762 1.731 Formula (5) 1.762 1.731 1.824 1.821 1.821 1.731 1.821 1.824 1.824 (6) 1.821 1.868 1.868 1.868 1.868 (7) (9) (11) (13) 2.18 2.10 1.79 1.79 1.79 (8) (10) ) (12) (14) -0.74 0.76 0.68 -0.90 -1.10

[0068]

As described above, according to the present invention, a collimator lens, a condenser lens, a focusing lens, which is suitable for an optical recording system adopting a multi-beam system,
Alternatively, it is possible to provide an optical recording lens having a wide image circle such as a tracking movable lens and a long working distance.

By cementing the third lens group or the fourth lens group together, axial chromatic aberration can be satisfactorily corrected while the flatness of the image surface is maintained, and out-of-focus shift due to changes in the oscillation wavelength of the light source can be prevented. can do.

[Brief description of drawings]

FIG. 1 is a lens diagram of an optical recording lens according to a first example.

FIG. 2 is a diagram of various types of aberration of the optical recording lens according to the first example.

FIG. 3 is a lens diagram of an optical recording lens according to a second example.

FIG. 4 is a diagram of various types of aberration of the optical recording lens according to the second example.

FIG. 5 is a lens diagram of an optical recording lens according to a third example.

FIG. 6 is a diagram of various types of aberration of the optical recording lens according to the third example.

FIG. 7 is a lens diagram of an optical recording lens according to a fourth example.

FIG. 8 is a diagram of various types of aberration of the optical recording lens according to the fourth example.

FIG. 9 is a lens diagram of an optical recording lens according to a fifth example.

FIG. 10 is a diagram of various types of aberration of the optical recording lens according to the fifth example.

FIG. 11 is a lens diagram of an optical recording lens according to a sixth example.

FIG. 12 is a diagram of various types of aberration of the optical recording lens according to the sixth example.

FIG. 13 is a lens diagram of an optical recording lens according to a seventh example.

FIG. 14 is a diagram of various types of aberration of the optical recording lens according to the seventh example.

FIG. 15 is a lens diagram of an optical recording lens according to an eighth example.

FIG. 16 is a diagram of various types of aberration of the optical recording lens according to the eighth example.

FIG. 17 is a lens diagram of an optical recording lens according to a ninth example.

FIG. 18 is a diagram of various types of aberration of the optical recording lens according to the ninth example.

FIG. 19 is a lens diagram of an optical recording lens according to a tenth example.

FIG. 20 is a diagram of various types of aberration of the optical recording lens according to the tenth example.

Claims (6)

[Claims] 1. A first lens group composed of a positive single lens having a convex surface facing the object side, a second lens group composed of a negative single lens having a concave surface facing the object side, and a positive third lens group. , A positive fourth lens unit having a convex surface directed to the object side and a fifth lens unit having a positive meniscus single lens having a convex surface directed to the object side, which are characterized by satisfying the following conditions: Optical recording lens to be. -0.47 <f / fa <-0.20 (1) 0.4 <(d4 + d3 / n2) / f <1.2 (2) -1.2 <(r3 + r4) / (r3-r4) <-0.4 (3) where f is The focal length of the entire system, fa is the combined focal length of the first and second lens groups, d4 is the optical axis spacing of the second and third lens groups, d3 is the optical axis thickness of the second lens group, and n2 is The refractive index of the second lens group, r3 is the radius of curvature of the object side surface of the second lens group, and r4 is the radius of curvature of the image side surface of the second lens group. 2. The optical recording lens according to claim 1, wherein the following condition is satisfied. n3> 1.60 (4) n4> 1.65 (5) n5> 1.70 (6) where n3 is the refractive index of the lens forming the third lens group, n4 is the refractive index of the lens forming the fourth lens group, and n5
Is the refractive index of the lenses constituting the fifth lens group. 3. The third lens group is configured by laminating a negative third lens and a biconvex positive fourth lens in order from the object side, and satisfies the following condition. 1
The optical recording lens described in. νdp / νdn> 1.6 (7) 0.80 <rC / f <1.4 (8) where νdp is the Abbe number of the positive lens that constitutes the cemented lens, νdn is the Abbe number of the negative lens that constitutes the cemented lens, and rC is It is the radius of curvature of the bonding surface. 4. The third lens group includes, in order from the object side, a positive third lens and a fourth negative meniscus lens having a concave surface facing the object side.
The optical recording lens according to claim 1, wherein the optical recording lens is configured by bonding with a lens and satisfies the following conditions. νdp / νdn> 1.6 (9) -0.90 <rC / f <-0.50 (10) where νdp is the Abbe number of the positive lens that constitutes the cemented lens, νdn is the Abbe number of the negative lens that constitutes the cemented lens, rC is the radius of curvature of the bonding surface. 5. The third lens group is a positive meniscus lens having a convex surface on the image side, and the fourth lens group has a negative meniscus fourth lens having a convex surface directed toward the object side in order from the object side. The optical recording lens according to claim 1, wherein the optical recording lens is configured by being attached to a fifth lens and satisfies the following condition. νdp / νdn> 1.6 (11) 0.55 <rC / f <1.0 (12) where νdp is the Abbe number of the positive lens that constitutes the cemented lens, νdn is the Abbe number of the negative lens that constitutes the cemented lens, and rC is It is the radius of curvature of the bonding surface. 6. The third lens group is a positive meniscus lens convex to the image side, and the fourth lens group includes a biconvex positive fourth lens and a negative fifth lens in order from the object side. The optical recording lens according to claim 1, wherein the optical recording lens is configured by bonding and satisfies the following conditions. νdp / νdn> 1.6 (13) -1.4 <rC / f <-0.72 (14) where νdp is the Abbe number of the positive lens that constitutes the cemented lens, νdn is the Abbe number of the negative lens that constitutes the cemented lens, rC is the radius of curvature of the bonding surface.