JPS6170519A - Large aperture condenser lens system - Google Patents

Abstract

PURPOSE:To improve an optical characteristic and facilitate processing, production, and inspection by using a single lens whose shape and various optical elements satisfy prescribed conditions. CONSTITUTION:The single lens is formed with the first surface whose convex is directed to the object side and the second surface whose concave is directed to the object side, and the second surface is a spherical surface and the first surface is an aspherical surface whose convergent refracting power is reduced toward the peripheral pat, and this aspherical surface is formed to a shape satisfying conditions of a formula I. When a curvature C, a refractive index (n), a focal length (f), etc. as references of the first surface are selected to satisfy conditions of a formula II, the spherical aberration and the coma aberration are compensated well to improve the optical characteristic. Since only one surface is the aspherical surface, processing, production, and inspection are made easier than those for a lens whose both surfaces are aspherical. In formulas, lM is the extent of deflection from the reference spherical surface in a maximum aperture part of the first surface and lZ is that from the reference spherical surface in the 0.7 aperture pat of the first surface.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a condensing lens system, and more particularly to a large-diameter condensing lens system consisting of a single lens.

Conventionally, there is an objective lens for reproducing video discs as disclosed in Japanese Patent Application Laid-Open No. 57-76512, but since both surfaces are aspherical, there are various problems in terms of processing, measurement, and manufacturing.

■Fish The present invention was made to solve the above problems, and provides a large-diameter condensing lens system that is a single lens, has a large-diameter high performance, and is relatively easy to process, manufacture, and inspect. The purpose is to

In order to achieve the above object, the present invention is a lens for converging light from a distant object point or parallel incident light, which has a first surface facing the object point side convexly and a first surface facing the object side. In a single lens consisting of a concave second surface, the second surface is a spherical surface, and the first surface is an aspherical surface whose convergent refractive power becomes weaker toward the periphery, and is a large-diameter condensing lens that satisfies the following conditions. System (L)4<69M/ΔQz(7(
2) 1.65/f <(n-1)C<1/f However, 69M is the deviation amount ΔQz from the reference spherical surface at the port large opening on the first surface.The reference spherical surface at the 0.7 opening on the first surface The deviation amount C1 from the first surface is the reference curvature n of the first surface, the refractive index j of the material constituting the lens, and f is '''/:

The present invention will be specifically described below based on examples.

FIG. 1 is a sectional view of a large-diameter condensing lens system to which the present invention is applied.

How to collect parallel incident light (condenser lens) and how to convert light emitted from a point into parallel light (collimator lens)
is widely used as a lens; however, both can be used equivalently by simply swapping the object and image. This lens was designed as a light projection lens (collimator) for L;S camera AF, but since it is easier to discuss the aberration of focused light than the aberration of parallel light, it will be described as a condensing lens system.

It can be applied to optical systems that do not require chromatic aberration correction (such as those that handle quasi-monochromatic light), such as light emitting lenses, light receiving lenses, lenses for optical disks, optical coupling lenses, collimators for lasers, etc. can be mentioned.

In principle, it is sufficient to correct aberrations only for axial light, but it is also necessary to correct aberrations for light with an angle of view of 0.5° to 1° due to deviation of a single point light source from the optical axis, eccentricity of the lens installation, inclination of the disk, etc. Therefore, the state of correction of the sine condition (SC) is also important as well as the spherical aberration (SA).

As is well known, the shape of the single lens for the above purpose is determined analytically as the SA minimum type.6 However, although it is the smallest type, the SA is largely undercorrected (as is well known, it is overfocused) and cannot be stopped down even when using high refractive index glass. It cannot be used unless the numerical aperture (NA) is small. JP-A-57-76512 solves this problem by using aspheric surfaces on both sides, but such a lens system is difficult to process because both surfaces must be made aspheric at the same time.
In particular, the difficulty in inspection and measurement is significant.6 The lens of the present invention was obtained by improving the above problems, and is a lens that focuses light from a distant object or parallel incident light, and has a convex surface toward the object side. In a single lens consisting of a first surface facing toward the object side and a second surface concave toward the object side, the second surface is a spherical surface and the first surface is an aspheric surface whose convergent refractive power becomes weaker toward the periphery. ΔQz=Amount of deviation from the reference spherical surface at the maximum aperture of the first surface ΔQ Amount of deviation from the reference spherical surface at the aperture of the first surface 067 C: Reference curvature n of the first surface: Consists of lens Refractive index of material (i) 4<ΔQM/ΔIlz<7 Equation (i) is a necessary condition for correcting SA sufficiently well at a large aperture of NA=o and +0.5. If the lower limit is exceeded, S
When A becomes significantly negative at the periphery and exceeds the upper limit where it is impossible to use a large NA (it has to be narrowed down), the balance between the aspherical low-order coefficient and the aspherical high-order coefficient is poor, and SA is in the middle. The light-gathering performance deteriorates due to swelling in the area.

Equation (11) relates to the refractive power shared by the first surface so that when the 1-spherical aberration is corrected, the coma aberration is simultaneously well maintained near the optical axis (SC is corrected).

If the refractive power exceeds the lower limit and the refractive power is small, the MSC will be negative and the coma will be undervalued, and if the upper limit is exceeded, the opposite will occur.In either case, the focusing effect of light with an angle of view will deteriorate, so it will be within the conditions. It is necessary to keep it within.

The face-to-face distance fid of a lens affects the Petzval sum and is effective in controlling S and C, but when aiming for compactness and light weight, it is often determined by the edge thickness required for processing and assembly. , therefore no limiting conditions are attached.

When used as an optical pickup lens, which will be described in an embodiment below, a cover glass or the like is installed near the image plane, and this glass plate has the role of automatically correcting SA.

Here, a case will be explained in which a cover glass is not used, but even if a cover glass is used, the gist of the invention does not change. In all Examples, f=l OO and the material is acrylic resin.

The formula for the aspheric surface of the first surface using λ = 780 nm as the emission center wavelength of the LED is: : Radius from the optical axis C: Curvature of the apex of the aspherical surface E: Eccentricity A4 to AH□: As the aspherical coefficient.

As a representative example, FIG. 1 shows the shape of Example 1.

Aberration diagrams of Examples 1 to 6 are shown in FIGS. 2 to 7, respectively.

SA: Spherical aberration SC: Sine condition DS: Spherical focal line (solid line) DM: Meridian focal line (dashed line) Example I
NA=0.4 b f :96.5 R+ =56.471 DI=30 N =1.
4839R2 = 279.573 E = 0.86586 A+ = -9,0394X10-9 A6 = -3,2702X 10 Δa = 8.3767X10 A,. = -9,3/106 X 10-+9Δf1M
=2.129 ΔQz=0.400 Therefore, the value of equation (i) is ΔQz/ΔQM =5.323(ii)
The value of the formula is (n-1)C=8.569X10=0.856
9/f Example 2 NA=0.45 b f =93.1 R+ =58.282 0=45 N=1
．． 4839R,! =-213,321 E =0.8784 A4 =-1,6049X10-" A6 =-3,2393X10 As =-2,5985X10 -+Q A+o = 3.4432X 10ΔQM=3.
627 From ΔQz=0.637, the value of equation (i) is ΔQM/ΔQz=5.694 Example 3
NA=0.5 b f =02.1 1-; No. 1 =58.2+6 D=5
0 N'=1.4839R2=-20
(i, 4 E = 0.88528 A 4 = 8.1343
97X]O A Io = -2,15:13
M=6. (ilO ΔQz=1.022 The value of equation (1) is ΔQ gate/ΔQz=6.468 The value of equation (11) is (n-1)c=8.312xlo=0.8312
/f Example 4 NA=0.38 b r =85.6 1e+ =65.539 1) = 58
N: 1.4839R2=131.56
4 1 piece = 1.17886 Δ< =1.297XlO A 6 = -6,2274X 10 Aa = -4,1554XIO AIo = 3.3311 X 10 △α = 1.397 ΔQz = 0. :985, the value of equation (i) is ΔQM/ΔQ z=4.9018 Example 5 NA=0.38bf=98 R=54.929 'D=22
N=1.4839R,! = −353
,396 1E=0.82798 A4 = 2.9829X10 Ab = -3,3648X 10 Aa = 2.1872 X 10-"Ago =-
1,2414 =0.88
1/f Example 6 N A =0.4b
f =96.5 R+ =56.4733 D=30
N = 1.4839R2 = -279,516 E = 0.86992 A 6 = 3.6144 X 10ΔQ = 2
．． 129 From ΔQz=0.399, the value of equation (,i,) is ΔQM/ΔQz=5.336(ii
) The value of the formula is (n-1)C=8.569XIO=0. J1
569/f Frog As described above, the large diameter condensing lens system of the present invention has a single lens with a large diameter and high performance, and is easy to process, manufacture, and inspect, and since the second surface is spherical, the number of cores can be reduced. , easy to install. Furthermore, if the lens is made of plastic, it will be lightweight, and if it is made by injection molding, it will be possible to produce it in large quantities at a significantly lower cost.

Further, since a large back focus can be obtained, a lens system having particularly excellent performance can be obtained as an optical pickup lens.

[Brief explanation of the drawing]

Figure 1 is a sectional view of the lens system of the present invention, Figure 2 is an aberration curve diagram of the embodiment, Figure 3 is an aberration curve diagram of the second embodiment, and Figure 4 is an aberration curve diagram of the third embodiment. 5 is an aberration curve diagram of the fourth embodiment, FIG. 6 is an aberration curve diagram of the fifth embodiment, and FIG. 7 is an aberration curve diagram of the sixth embodiment.

Claims (1)

[Scope of Claims] A lens for converging light from a distant object point or parallel incident light, which has a first surface facing the object point side convexly and a second surface facing the object side concavely. In the single lens consisting of, the second surface is a spherical surface and the first surface is an aspheric surface whose converging refractive power becomes weaker toward the periphery, and the large-diameter condensing lens system (1) 4<Δl_M satisfies the following conditions. /Δl_Z<7 (2) 1.65/f<(n-1)C<1/f However, Δl_M is the deviation amount from the reference spherical surface at the maximum aperture of the first surface. Δl_Z is the 0.7 aperture of the first surface. The amount of deviation C1 from the reference spherical surface at the first surface is the reference curvature n of the first surface, the refractive index f of the material constituting the lens, and the focal length of the lens.