JPS62196613A - Aspheric lens - Google Patents

Abstract

PURPOSE:To obtain an inexpensive aspheric lens with superior optical performance by reducing the difference between the refractive indexes of a lens blank consisting of a glass lens and a plastic layer joined with the surface of the lens blank. CONSTITUTION:In the aspheric lens obtained by joining the plastic layer 1 to the surface of the lens blank consisting of a glass lens and forming the surface of the plastic layer as an aspheric surface, the difference between the refractive index based upon the main wavelength of the glass and that based upon the main component of plastic is set up to DELTAnXa/P<=5X10<-5>. Provided that, (a) and P are the roughness of the surface shape of the lens blank and its pitch. Namely, when the surface shape index a/P of the lens blank is reduced so that an incident angle alpha is reduced, the difference DELTAtheta between the refractive angles is reduced, or when the difference DELTAn between the refractive indexes of the glass and plastic is reduced (the ratio n1/n2 of both the refractive indexes is reached to '1'), the difference DELTAtheta of the refractive angles is also reduce, so that the excellent optical performance can be obtained.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to an aspherical lens suitable for use in video cameras, etc., and in particular, it relates to an aspherical lens suitable for use in video cameras, etc. This invention relates to an aspherical lens whose layer surface is aspherical.

[Conventional technology]

In recent years, video cameras and projection televisions.

Aspherical lenses are used as lenses for video discs and the like in order to reduce the number of lenses in these optical systems and improve optical performance.

By the way, conventionally, it has been very difficult to make the surface of a glass lens into an aspherical lens. An aspherical lens has been proposed in which a transparent plastic layer is bonded to a blank surface and the surface of this plastic layer is made into an aspherical surface. According to such an aspherical lens, the surface of the plastic layer can be made into an aspherical surface of any shape, and the surface of the glass lens is polished, so that light at the interface between the glass lens and the plastic layer is reduced. Excellent optical performance can be obtained by preventing refraction.

[Problem that the invention seeks to solve]

However, in the above-mentioned conventional technology, polishing work of the glass lens requires a long time, and the glass lens used as a lens blank becomes very expensive. The cost of an aspherical lens with a plastic layer bonded to the surface of a lens blank mainly consists of the cost of the lens blank and the cost of bonding the plastic layer. The blank aspherical lens was very expensive.

An object of the present invention is to solve the problems of the prior art and provide a low-cost aspherical lens with excellent optical performance.

[Means for solving problems]

In order to achieve the above object, the present invention reduces the difference in refractive index between a lens blank made of a glass lens and a plastic layer bonded to the surface of the lens blank.

[For production]

Even if the surface of a glass lens used as a lens blank is rough, refraction of light at the interface between the lens blank and a plastic layer is suppressed, and excellent optical performance can be obtained using an inexpensive glass lens that is not polished as a lens blank.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a sectional view showing an embodiment of an aspherical lens according to the present invention, in which 1 is a plastic layer, 2 is a lens blank, and 3 is a boundary surface.

In the figure, a plastic layer 1 is bonded to the surface of a lens blank 2, which is a glass lens, and the surface of this plastic layer 1 has an aspherical surface of a predetermined shape. Since the surface of the lens blank 2 is not polished, the interface 3 between the lens blank 2 and the plastic layer 1 is rough and has uneven parts.

FIG. 2 is an enlarged view of the interface 3 between the lens blank 2 and the plastic layer 1 in FIG. 1.

As shown in FIG. 2, since there are uneven portions on the boundary surface 3, light rays are incident on this boundary surface 3 at an angle, and the light is refracted. Therefore, in FIG. 2, it is assumed that the cross-sectional shape of the boundary surface 3 is a sine curve, and nl + n
If t is the refractive index of glass and plastic, respectively, P and a are the pitch and surface roughness of the shape of the interface 3, and α is the maximum inclination angle of the tangent to the interface 3, then the maximum inclination angle α of the interface 3 is The light rays incident on the part are refracted to the maximum. The incident angle of this light ray is α, and the incident angle α, outgoing angle β, and outgoing angle Δθ are expressed as follows.

7w tB n-’□π Difference in refractive index between glass and plastic Δn (n.

The relationship between the refraction angle Δθ and the roughness a of the interface 3
FIG. 3 shows each value of the lens blank surface shape index a/P expressed as the ratio of the pitch P to the lens blank surface shape index a/P. As is clear from the figure, the lens blank surface shape index a
If /P is made smaller so that the angle of incidence α becomes smaller,
The difference in refractive angle Δθ is reduced, or the difference in refractive index Δn between glass and plastic is reduced (i.e.,
When the ratio nl/nz of both refractive indexes approaches 1), the refraction angle Δθ becomes small and excellent optical performance is obtained.

By the way, in the case of an aspherical lens used in a video camera, the allowable range of the refraction angle Δθ is ±0.
It is within 006'. Lens blank surface shape index a / for refraction angle Δθ to satisfy this tolerance range
The relationship between P and the allowable refractive index difference it (that is, the allowable refractive index difference) Δn0 is shown in FIG.

That is, the lens blank surface shape index a/P and the allowable refractive index difference Δn have a substantially inversely proportional relationship, which is represented by the curve shown in FIG. 4. This curve has Δn X a /
This represents the relational expression of P -5Xl0-'. Therefore, the glass and plastic layer 1 of the lens blank 2
As a plastic material, the difference between these refractive indexes Δn
However, Δn X a / P≦5 X 10-' --
----------- (Use one that satisfies 11.

This results in acceptable optical performance.

From equation (1), the smaller the lens blank surface shape index a/P, the larger the refractive index difference Δn can be.

However, in order to reduce the lens blank back surface shape index a/P, the surface of the lens blank 2 needs to be polished. FIG. 5 shows the relationship between the lens blank surface shape index a/P and the manufacturing time including machining and polishing work of the lens blank 2.
When a/p > 0.01, a simple polishing process of 2-3 times is sufficient after cutting the lens blank by machining, but when a/p < 0.01, additionally,
The polishing process must be repeated several times to several tens of times, and it takes a very long time to produce the lens blank 20, making the lens blank 2 very expensive. Therefore, in order to reduce the production time and cost of the lens blank 2, the lens blank surface shape index a/
It is necessary that P be 0.01 or more.

For this purpose, in FIG. 1, the lens blank surface shape index a/P of the lens blank 2 is set to be 0.01 or more, preferably 0.02 or more, and the difference in refractive index Δn between the lens blank 2 and the plastic layer 1 is is made to satisfy the above formula (1). As a result, in this embodiment, an inexpensive glass lens can be used as the lens blank 2, and excellent optical performance can be obtained.

In addition, the lens blank surface shape index a/P is 0.0
If it is 1 or more, lens blank 2 and plastic layer 1
The permissible difference Δn in refractive index with respect to the lens blank is 0.005 or less, and if the lens blank surface shape index a/P is 0.02 or more, the difference Δn in refractive index may be 0.0025 or less.

By the way, the difference in refractive index Δn must satisfy the above-mentioned condition 2 (1) for various wavelengths, and for this purpose, the difference in Atsube number ν5 between the lens blank 2 made of glass and the plastic layer l must be must also be small. d-line (wavelength λa
= 587, 56 nm), C line (wavelength λ. = 65
(i, 28 nm), F-line (wavelength λp = 486.1
Na, Nc, NF
Then, the Atsube number ν is expressed as follows.

If the Abbe number ν4 and the refractive index N4 are the same, the refractive index at each wavelength will also be approximately the same. In order to make the difference Δn in the refractive index for each wavelength between the lens blank 2 and the plastic N1 0.005 or less as described above, the difference in their Abbe numbers ν4 should be 20 or less, and, Similarly, in order to make the difference Δn in refractive index 0.0025 or less, these Atsbe numbers ν are required.

The difference should be 10 or less. However, considering the achromatic effect, they were set to 10 or less and 5 or less, respectively.

Figure 6 shows the possible ranges of the refractive index Nd and Atsube number ν of various glasses and plastics, and the difference Δn in the refractive index N4 is 0.005 or less, preferably 0.00.
25 or less and the difference in Atsube number ν4 is 10 or less, preferably 5
The following glass and plastic materials are used to form the lens blank 2. shown in FIG. It can be used as a plastic layer. In this way, the refractive index is almost the same as that of plastic,
Glasses with Atsube numbers include Ba5F, F, and LF.
, BaF.

LLF, BaLF, KzF, KF, ZK, Ni, BK, F
There are K, etc.

FIG. 7 is a sectional view showing another specific example of the lens blank 2 in FIG. 1, and 4 is a flange portion.

In this specific example, a collar portion 4 having a flat portion is provided on the outer peripheral portion of the lens blank 2 .

Next, a method of bonding the plastic layer to the lens blank 2 will be explained using FIG. 8. In the figure, 5a and 5b are molds, 6a+6b are aspherical surface forming parts, and 7a and 7b are flat parts.

In the figure, molds 5a and 5b are made of quartz or the like that transmits ultraviolet rays, and have aspherical portions 6a and 6b and flat portions 7a and 7b. Lens blank 2 is mold 5a
, 5b, the collar portion 4 of the lens blank 2
The flat parts of the molds 5a and 5b come into contact with the flat parts 7a and 7b of the molds 5a and 5b, so that the collar part 4 is clamped. This prevents the lens blank 2 from tilting with respect to the molds 5a and 5b. Type 5a, 5
When a plastic material is injected into the gap between the aspherical surface forming portions 6a and 6b of b and the lens blank 2 and ultraviolet rays are projected, the plastic material hardens and becomes the plastic layer 1.
Joined with lens blank 2. Therefore, the surface shape of the aspherical surface forming portions 6a, 6b is transferred to the surface of the plastic layer 1 on the side that is in contact with the aspherical surface forming portions 6a, 6b of the molds 5a, 5b, and the surface shape is a predetermined aspherical surface. Become.

In this way, by providing the collar portion 4 on the lens blank 2, the lens blank 2 is not tilted with respect to the molds 5a and 5b, and the plastic layer 1 is not bonded at an angle with respect to the lens blank 2. Since the thickness of the gap between the lens blank 2 and the molds 5a, 5b is determined from the thickness of the flange portion 4, the thickness of the plastic layer 1 to be bonded can be controlled with high precision. According to this specific example,
The precision of the aspherical surface formed on the surface of the plastic layer 1 will be significantly improved to about 1/2 that of the conventional one.

Next, several specific examples of the above embodiments and a comparative example for comparison with these examples will be described. In addition, the materials of glass and plastic in each specific example and comparative example, and the refractive index N4
1 Atsube number 4. Lens blank surface shape index a/
P and their evaluations are summarized in the attached table.

Evaluation is performed on a single lens by visually judging the degree of scattering by transmitted light and visually judging the sharpness of the lines when looking at the substrate's own pattern through the lens, and determining whether it has commercial value as a high-precision aspherical lens. It was decided.

(Specific Example 1) The material of the lens blank is 2 (d-line (wavelength 587.
refractive index na = 1.5L6(1
2, Atsbe number ν, =56.8) was used. The lens blank was manufactured by machining, and the surface roughness a = 0.4 μm.
, pitch P=20 μm. That is, the lens blank surface shape index a/P=0.02. The plastic bonded to this lens blank is methyl α-chloroacrylate (refractive index n, = 1.5172.
The Atsube number was 57).

The refractive index difference Δn between glass and plastic is 0.0012°, and the difference in Atsube number ν is 0.2. Product of lens blank surface shape index and refractive index difference a/P x Δn-2XI
O"'.

Aspherical lenses obtained by bonding these glasses and plastics had excellent evaluations of scattering and sharpness.

(Specific Example 2) The material of the lens blank is 10 (refractive index n4-1.
50137. Atsbe's number νa = 56.4) was used. The lens blank is manufactured by machining and has a surface roughness of a-0.
, 3 μm, and pitch P-15 μm. The lens blank surface shape index a/P = 0.02. The plastic bonded to this lens blank is decamethylene glycol dimethicrylate (refractive index n4-1.499
0. Atsbe number ν, =56.3).

The refractive index difference Δn between glass and plastic is 0.0024°, and the difference in Abbe's number is 0.1. Product of lens blank surface shape index and difference in refractive index ν4 a/p XΔn=4.8
XIO-'.

Aspherical lenses obtained by bonding these glasses and plastics had excellent scattering and sharpness.

(Specific example 3) LLF2 (refractive index na
=1.54072. The Atsbe number νm-47,2) was used.

The lens blank is manufactured by machining, and has a surface roughness of a
=0.4 I! m+ pitch P=20A! It was set as m. The lens blank surface shape index a/P = 0.02. The plastic bonded to this lens blank was methyl methacrylate (refractive index na "1.5398, Abbe number ν, -47.5).

The refractive index difference Δn between glass and plastic is 0.0009°, and the difference in Atsube number ν is 0.3. Product of lens blank surface shape index and refractive index difference a/p XΔn=1.8
XIO-'.

Aspherical lenses obtained by bonding these glasses and plastics had excellent scattering and sharpness.

(Specific example 4) The material of the lens blank is KF8 (refractive index n.

= 1.51118. The Atsbe number νa = 51.0) was used. The lens blank was manufactured by mechanical processing, and the surface roughness a = 0.8 μm and the pitch P = 20 μm. The lens blank surface shape index a/P = 0.04.

The plastic bonded to this lens blank is 1-methyl-cyclohexyl methacrylate (refractive index n, -1,
5111, Atsbe number νm ”'54).

The refractive index difference Δn between glass and plastic is 0.0001°, and the difference in Atsushi's number C is 3. Product of lens blank surface shape index and refractive index difference a/PXΔn=0.4X 10-
'is.

Aspherical lenses obtained by bonding these glasses and plastics had excellent scattering and sharpness.

(Specific example 5) The material of the lens blank is LF6 (refractive index n.

-1,56732, Atsbe number νa = 42.8). The lens blank is manufactured by machining and has a surface roughness of a
= 0.8 μm, pitch P-10 μm. The lens blank surface shape index a/P = 0.08. The plastic bonded to this lens blank is methyl α-bromoacrylate (refractive index n 4 = 1.5672+
The Atsbe number νa was set as 46.5).

The refractive index difference Δn between glass and plastic is (1,0001
The difference in the Atsube number ν4 is 3.7. Product of lens blank surface shape index and refractive index difference a/p XΔn = 0
．． It is 8×10″S.

Aspherical lenses obtained by bonding these glasses and plastics had excellent scattering and sharpness.

(Specific example 6) LF3 (refractive index n6=
1.58215. The Atsbe number νa -42,1) was used. The lens blank is manufactured by machining, and the surface roughness a=
The pitch was 0.8 μm and the pitch P was 20 μm. The lens blank surface shape index a/P = 0.04. The plastic bonded to this lens blank is 0-chlorobenzyl methacrylate (refractive index n, = 1.5823°, Abbe number νd-37).

The refractive index difference Δn between glass and plastic is o, oooi.

The difference in Atsube number ν4 is 5.1. Product of lens blank surface shape index and refractive index difference a/p xΔn=o, 4
X 10-'.

Aspherical lenses obtained by bonding these glasses and plastics had excellent scattering and sharpness.

(Comparative Example 1) The materials of the lens blank and plastic were the same as those of Example 1. It was designated as methyl α-chloroacryle-1.

The surface shape of the lens blank was different from that of Example 1, and the surface roughness a = 1. Otl ITl+ Pitch P-20
It was set as μm. Lens blank surface shape index a/P
=0.05. Product a/PxΔn of lens blank surface shape index and refractive index difference: 6. OXl0-'.

In this case, the obtained aspherical lens had excellent scattering but poor sharpness.

(Comparative Example 2) KF3 (refractive index n4-
1.51454. Atsbe's number ν, =54.7) was used. The lens blank is manufactured by machining and has a surface roughness of 2w0.
The pitch was 94 μm and the pitch P was 20 μm. The lens blank surface shape index a/P-0,02. The plastic bonded to this lens blank was methyl isopropyl ketone (refractive index n a '' 1.5200, Abbe number ν4-54.5).

The refractive index difference Δn between glass and plastic is 0.0055°, and the difference in Abbe number νd is 0.2. The difference between the lens blank surface shape index a/P and the Atsube number ν4 is the same as in Example 1, but the refractive index difference Δn is larger. Product of lens blank surface shape index and refractive index a/P x
Δfl −11, OX 10−′.

Aspherical lenses obtained by bonding these glasses and plastics had deteriorated both in scattering and sharpness.

(Comparative Example 3) ZK4 (refractive index n4-1) was used as the material of the lens blank.
．． 51190. The Atsbe number νa = 58.1) was used.

The lens blank is manufactured by machining and has a surface roughness of a=0.
The pitch was 4 μm, and the pitch P was 20 μm. The lens blank surface shape index a/P = 0.02. The plastic bonded to this lens blank was β-methallyl methacrylate (refractive index n a = 1.5110, Atsbe number C = 47).

The refractive index difference Δn between glass and plastic is 0.0009°, and the difference in Atsushi's number C is 11. The lens blank surface shape index a/P and the refractive index difference Δn are the same as in Example 3, but the difference in the Atsube number ν4 is large (the product of the lens blank surface shape index and the refractive index difference a/P) p
n-1,8Xl0-'.

Aspherical lenses obtained by bonding these glasses and plastics had excellent sharpness but poor scattering.

As can be seen from the results of the above specific examples 1 to 6 and comparative examples 1 to 3, the product of the lens blank surface shape index a/p and the refractive index difference Δn must satisfy a/P x Δn≦5X10-'. Optical performance has deteriorated.

Furthermore, in a lens blank that is not polished, the lens blank surface shape index a/P is around 0.02, so the refractive index difference Δn between glass and plastic is 0.02.
Furthermore, in order to reduce the cost of lens blanks, the refractive index difference Δn must be 0.0 or less.
It is preferable to set it to 02 or less.

In addition, if the difference in Atsube number between glass and plastic exceeds 10, the optical performance will deteriorate, so the difference in Atsube number must be kept below 10.This difference in Atsube number should also be below 5 when further cost reduction is taken into consideration. It is preferable to

In addition, in Specific Examples 1 to 6 and Comparative Examples 1 to 3, the shape of the aspherical lens was a convex lens with an outer diameter of 30 m+ and a wall thickness of 1 (L++ m). However, there is no problem even if the shape is a concave lens. Outer diameter used: 12
There is no problem even if the lens has a large diameter and thick wall such as 0 mm and wall thickness of 30 mm.

In addition, in the above embodiment, an ultraviolet curing agent is mixed with the plastic material, and as explained in FIG.
The plastic layer and glass lens blank were bonded together by projecting ultraviolet light from both sides. However, in the present invention, the lens blank and the plastic layer are not only bonded by ultraviolet curing, but also may be bonded by thermosetting or the like.

Further, in the above embodiments, the lens blank was produced by mechanical processing, but it may also be produced by press processing.

As described above, in the above embodiment, the lens blank surface shape index of the lens blank can be set to 0.01 or more, and the lens blank surface shape index a/P can be set to 0.0001.
Compared to the conventional technology in which lens blanks were finished to a certain extent, the time and cost for producing lens blanks could be reduced to 115% or less.

(Effects of the Invention) As explained above, according to the present invention, by reducing the difference in refractive index between the glass lens blank and the plastic layer, it is possible to use an inexpensive unpolished glass lens blank. As a result, the manufacturing time and cost of the lens blank can be significantly reduced, and an aspherical lens having excellent optical performance can be provided at low cost.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing an embodiment of an aspherical lens according to the present invention, FIG. 2 is an enlarged sectional view of the interface between the glass lens blank and the plastic layer in FIG. 1, and FIG. A graph showing the relationship between the refractive index difference and the refraction angle. Figure 4 is a graph showing the relationship between the surface shape index of the interface between glass and plastic and the refractive index difference. Figure 5 is a graph showing the relationship between the lens blank surface shape index and the lens blank. 6 is a graph showing the relationship between the refractive index and Atsube number of glass and plastic. FIG. 7 is a sectional view showing another example of the lens blank in FIG. 1. FIG. 8 is an explanatory diagram showing a specific example of a method of joining the lens blank shown in FIG. 7 and the plastic layer. 1... Plastic layer, 2... Lens blank (glass), 3... Interface between glass and plastic, 4...
...Brim part, 5a, 5b... Mold, 6a, 6b... Aspherical surface forming part, ? a, 7b...Plane portion. Figure 1! Fig. 2 Fig. 3 苅萭笈Δn Fig. 4 Moon E interface shape 1 person 1 sho a o/p Fig. 5 Lens °Bufunk surface NtK4 $1 (5 i b Fig. 6 mi/, 8- Fig. 7

Claims (1)

[Claims] 1. In an aspherical lens in which a plastic layer is bonded to the surface of a lens blank made of glass and the surface of the plastic layer is made an aspherical surface, the refractive index at the main wavelength of the glass and the refractive index of the plastic The difference Δn from the refractive index at the main wavelength is Δn×a/P≦5×10^-^5, where a and P are the surface roughness and pitch of the surface shape of the lens blank, respectively. Aspherical lens. 2. In claim 1, the refractive index difference Δ
An aspherical lens characterized in that n is 0.005 or less, preferably 0.0025 or less. 3. An aspherical lens according to claim 1 or 2, characterized in that the difference between the Atsube number of the glass and the Atsube number of the plastic is 10 or less, preferably 5 or less. 4. An aspherical lens according to claim 1, 2, or 3, characterized in that a collar portion having a flat surface is provided on the outer peripheral portion of the lens blank.