JPH03288811A - Photographing lens - Google Patents

Abstract

PURPOSE:To prevent the performance of the photographing lens from being dropped due to a change in temperature and to inexpensively attain high efficiency by providing the photographing lens with plural plastic lenses and one glass lens, constituting the plastic lenses in the pregroup as an afocal optical system and constituting the object side face of the rear group lens so that the incident angle of light projected from the glass lens is made vertical. CONSTITUTION:One glass lens 5 is arranged on the intermediate position among plural plastic lenses 2 to 4 and the lens 5 is provided with an image forming function. The plastic lenses 2, 3 in the pregroup divided through the lens 5 are constituted as an almost afocal optical system and the object side face of the lens 4 in the post group is formed so as to have a curvature face on which the incident angle of light projected from the lens 5 is almost vertical. Namely, the performance of the rear group can be prevented from being dropped due to a change in temperature by making the light projected from the lens 5 incident upon the object side face RA8 of the 4th plastic lens 4 almost in the vertical direction. Consequently, the drop of photographing performance due to the temperature change or a change on a focal position can be prevented and the inexpensive photographing lens with high performance can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a photographic lens used in electronic cameras and the like, and particularly to a photographic lens that is a hybrid of a plastic lens and a glass lens.

Our goal is to provide high-performance photographic lenses.

[Background of the Invention 1 Conventionally, photographing lenses used in electronic cameras are generally composed of only glass lenses. However, since glass lenses must be manufactured by polishing them one by one, productivity is low and costs are high. For this reason,
Recently, consideration has been given to using plastic lenses with good productivity. However, plastic lenses have a large change in refractive index due to temperature changes, and their photographic performance and focal position change greatly depending on temperature changes, making it difficult to produce high-performance lenses, so they are not often used as photographic lenses. is the current situation.

[Purpose of the Invention] This invention was made in view of the above-mentioned circumstances, and its purpose is to prevent the deterioration of photographic performance and change in focal position due to temperature changes, and to provide an inexpensive and high-performance method. In order to achieve the above-mentioned object, the invention arranges one glass lens between a plurality of plastic lenses,
Only this glass lens has an imaging function, and the plastic lens in the front group is configured into an almost afocal optical system with the glass lens as a boundary, and the object side of the plastic lens in the rear group is configured to It is formed on a curvature surface where the incident angle of the light ray is approximately perpendicular.

The present invention also provides an optical system comprising a plurality of plastic lenses and one glass lens, in which only the glass lens has an imaging function, and all of the plurality of plastic lenses are configured into an almost afocal optical system. It is.

[First embodiment] Hereinafter, with reference to FIGS. 1 and 2, the first embodiment of the present invention will be described.
An example will be explained.

FIG. 1 shows the configuration of a photographic lens. This photographic lens l includes three plastic lenses 2 to 4, one glass lens 5, a protective glass 6, and an aperture plate 7.
The second and fourth lenses are plastic lenses 2 to 4, the third lens is a glass lens 5, and an aperture plate 7 is placed between the second plastic lens 3 and the third glass lens 5. In addition, the image plane 8 is arranged behind the fourth plastic lens 4 with a protective glass 6 interposed therebetween. In this case, three plastic lenses 2-4
is made of acrylic resin (PMMA) or polycarbonate (PC).
) and other transparent synthetic resin materials. The glass lens 5 is made of optical glass or the like. The first plastic lens 2 is a meniscus convex lens with a concave surface facing the object side, and the image side surface RA2 is formed into an aspherical surface. The second plastic lens 3 is a meniscus concave lens with a concave surface facing the object side, and the image side surface RAa is formed into an aspherical surface. What is important here is that the first and second plastic lenses 2 and 3 are constructed into an almost afocal optical system to prevent the optical performance of the front group from deteriorating due to temperature changes. Further, the third glass lens 5 is a biconvex lens, and only this glass lens 5 has an imaging function. The fourth plastic lens 4 is a concave lens with a convex surface facing the object side, and its object side surface RAa is formed as follows. That is, the object side surface RAs of the fourth plastic lens 4 is formed into a curvature surface such that the incident angle of the light beam emitted from the glass lens 5 is substantially perpendicular. In other words, it is formed into a surface of curvature close to a spherical surface centered on the imaging center of the glass lens 5. This is to prevent the performance of the rear group from deteriorating due to temperature changes by making the light beam emitted from the glass lens 5 almost perpendicularly incident on the object side surface RAs of the fourth plastic lens 4.

That is, the photographing lens 1 described above has the following (a) to (
The configuration satisfies the condition h).

(d) -10<DEG2<410 (e) 1.6<n:+<1.8(f) 45
<ν3<65 (g) h-07<RA7< (h-07) X L
, 5(h) (f3-(Dz+Ds)l Xo, 8 <
RAa <f3-(Dz+Da) where fl is the focal length of the i-th lens, ! r~” is j from the i-th lens
The focal length of the partial system up to the ith lens, DECi is the angle (degree) at which the exit ray from the ith lens (ray bundle within the aperture range of the optical system) enters the next lens, n
l is the refractive index of the first lens, ν1 is the Abbe number of the i-th lens, RAi is the paraxial radius of curvature, and Di is the center thickness.

The above condition (a) is for limiting the focal length of the entire system to 0.8 to 1.4 times that of the third glass lens 5.
If it is below 0.8, the two plastic lenses in the front group 2
．． 3 becomes disadvantageous in aberration correction, and if it exceeds 1.4, the focal length of the fourth plastic lens 4 becomes short, making hot water temperature correction disadvantageous.

Condition (b) is to limit the focal length of the fourth plastic lens 4 with respect to the focal length of the entire system, and is -1,9
If it is less than 4, temperature correction becomes disadvantageous.

If the value exceeds -1.55, aberration correction becomes disadvantageous.

Condition (C) is a restriction on the afocal magnification when the partial system consisting of two 2°3 plastic lenses in the front group is regarded as afocal; if it is lower than 0.6 times, aberration correction becomes disadvantageous; When the magnification is increased to 9 times or more, the focal length of the entire system becomes long, leading to an increase in spherical aberration.

The purpose of condition (d) is to limit the exit angle of the light rays from the two plastic lenses in the front group so as to approach the afocal angle, thereby reducing changes in the exit angle due to temperature changes.

Conditions (e) and (f) are for limiting the material of the glass lens 5. If the refractive index n3 is lower than S, the curvature becomes thicker and increases aberrations, and if it is 1.8 or higher, the material cost increases. is about 20 to 30 times more expensive than normal ones, and if the number ν3 is 65 or more, there is no suitable material available.
If it is less than 45, correction of chromatic aberration becomes disadvantageous.

, I% cases (g) and (b) limit the radius of curvature of the object side surface R^8 of the fourth plastic lens 4 in the rear group, so that the incident angle of the light ray to the fourth plastic lens 4 can be approximately adjusted. This is to make the lens vertical and reduce focus shift (shift in focus position) due to temperature changes.

In this way, the above-mentioned photographic lens 1 mainly consists of plastic lenses 2 to 4, and only one glass lens 5 is used, so it is highly productive and can be manufactured at low cost. The plastic lens 2.3 in the front group is configured as an almost afocal optical system, and the object side surface R^8 of the fourth plastic lens 4 in the rear group is configured to have an image effect. Since the lens is formed on a curved surface where the incident angle is almost vertical, there is little deterioration in photographing performance or change in focal position due to temperature changes, and high performance can be obtained. In this case, among the plastic lenses 2.3 in the front group, especially the image side surface R^2 of the first plastic lens 2 is formed into an aspherical surface to effectively correct aberrations such as distortion. I can do it.

Incidentally, Tables 1 and 2 show specific examples where the above-mentioned photographic lens 1 is actually applied to an electronic camera.
In Table 1, f: 5, F: 2.8, imaging range (image circle): φ4.4 Table 2 shows the aspherical coefficient of the image side of the first plastic lens 2. .

However, the shape of the aspherical surface in Table 2 is determined by defining the optical axis direction as two directions and the direction perpendicular to the optical axis as the X direction.
When the displacement in two directions of the point shifted by xd in the X direction from the apex on the optical axis of
・Xdz)+α2Xd4+ a3Xd6+ aaXd8
+a5Xd10. (however,
C is 1/R in the paraxial region. ) In such photographic lens 1 of Tables 1 and 2,
It goes without saying that it is possible to obtain high-performance images with very little deterioration in photographic performance or change in focus position due to temperature changes, and the #f has no aberrations such as spherical aberration, astigmatism, and daystone 1 f. Since the curves are as shown in (A) to (C), it can be seen that the aberrations are well corrected.

[Second Embodiment] Next, referring to FIGS. 3 and 4, a second embodiment of the present invention will be described.
An example will be explained.

FIG. 3 shows the configuration of a photographic lens according to the second embodiment. This photographic lens lO includes four plastic lenses 11 to 14.
One glass lens 15 is arranged in the rear group, and a maintenance glass 16 is interposed behind this glass lens 15 to form an image plane 1.
7 and the second plastic lens 12 and 3
The configuration is such that an aperture plate 18 is arranged between the second plastic lenses 13. In this case, each lens 11-15
is made of the same material as in the first embodiment described above. The first plastic lens 11 is a meniscus concave lens with a convex surface facing the object side, and the image fM surface RB2 is formed as an aspheric surface. The second plastic lens 12 is a biconvex lens. The third plastic lens 13 is a biconcave lens. The fourth plastic lens 14 is a biconvex lens, and the object side surface RB8 is formed into an aspherical surface. The fifth glass lens 15 is a biconvex lens, and only this glass lens 15 has an imaging function. What is important here is that all of the first to fourth plastic lenses 11 to 14 are constructed into an almost afocal optical system to prevent the optical performance of the front group from deteriorating due to temperature changes.

That is, this photographic lens 10 has the following (a) to (f)
) has a configuration that satisfies the following conditions.

(a) 1.45<n+, nz, ns<
1.6(b) 55< y + , ν2 , ν4<
65(c) 1.55<ns<1.85 and 25
<ν3<35(d) L, S < n s < 1.7
and 55<y5<85(e) -0,3
<-<+ 0, 3f1-4 (f) -10<DEG9<+10 However, RBi represents the paraxial radius of curvature, and the other symbols represent the same as in the first embodiment.

Conditions (a) and (b) described above are based on the four conditions (C
) is the 0 condition (d) in which the third plastic lens 13 is limited to a material with high refraction and high dispersion (for example, polycarbonate, etc.), thereby suppressing chromatic aberration among the four plastic lenses 11-14. is glass lens 15
0 conditions (e) (f
) relates to the focal length of the partial system of the four plastic lenses 11 to 14, and is intended to limit the entire partial system to an almost afocal optical system to reduce fluctuations in the focal position due to temperature changes. Also, for aspherical surfaces, 1
The image side surface RB2 of the fourth plastic lens 11 is effective for correcting distortion, and the object side surface RBg of the fourth plastic lens 14 is effective for correcting spherical aberration.

Such a photographic lens 10 also has similar effects, and can also provide particularly bright brightness.

Incidentally, Tables 3 and 4 show specific examples in which the above-described photographic lens 10 is actually applied to an electronic camera. In this case, Table 3 shows f: 5mi+, F: 2.0, imaging range (image Circle): φ4,4 is 0 table 4 is 1
The aspheric coefficients of the object side surface RBI and image side surface RB2 of the second plastic lens 11 and the object side surfaces RB3° and RB8 of the second and fourth plastic lenses 12 and 14 are shown.

Table 4 Table 3 However, the shape of the aspherical surface is expressed by the same formula as in the above-mentioned embodiment.

The photographing lenses 1O in Tables 3 and 4 have similar effects, and in particular, aberrations such as spherical aberration, astigmatism, and distortion are reduced as shown in Figures 4 (A) to (C). Because it becomes a curve.

It can be seen that the aberrations are well corrected.

[Third Embodiment] Next, referring to FIGS. 5 and 6, a third embodiment of the present invention will be described.
An example will be explained.

FIG. 5 shows the configuration of a photographic lens according to a third embodiment. This photographic lens 20 has two plastic lenses 2223 arranged in the rear group of one glass lens 21, with a protective glass 24 interposed behind them. The configuration is such that the image plane 25 is arranged in such a manner as to In this case, each lens 21-23 is made of the same material as in the embodiment described above. The first glass lens 21 is a meniscus convex lens with a convex surface facing the object side, and only this glass lens 21 has an imaging function. The second plastic lens 22 is a concave lens. The third plastic lens 23 is a meniscus convex lens with a convex surface facing the object side, and both surfaces RCs and RCb are formed into aspherical surfaces. What is important here is that the second and third plastic lenses 22 and 23 are constructed into an almost afocal optical system to prevent the optical performance of the front group from deteriorating due to temperature changes.

That is, this photographic lens 20 has the following (a) to (f)
) has a configuration that satisfies the following conditions.

(a) 1.55< n + < 1.85 and 4
0< p H<80 (b) 1.5 < n 2 <
L, S Ka25<F2<35(c) 1.4
5<n3<1.55 and 50<y:l
<65(f) -10<DEG2-DEG6 <+1
0 However, RC represents the paraxial radius of curvature, and each symbol other than this represents the same as in the first embodiment.

The above condition (a) is to limit the material of the first glass lens 21 to a material with high refraction and relatively low dispersion, and if the material has a higher refraction than the range of condition (a), The first condition (b) is that the material of the second plastic lens 22 is limited to one with high dispersion and high refractive index. The 0 condition (c), which is for the purpose of The reason for (f) is to limit the combined focal length of the two plastic lenses 22 and 23 to an almost afocal optical system to reduce fluctuations in the focal position due to temperature changes.

Such a photographic lens 20 also has substantially the same effects as those of the embodiments described above, and in particular, the number of lenses can be extremely reduced.

By the way, Tables 5 and 6 show specific examples in which the above-described photographic lens 20 is actually applied to an electronic camera. In this case, Table 5 shows f: 8 mm, F: 2.0, imaging range (image Table 6 shows the aspheric coefficients of the object side RCs and the image side RC6 of the third plastic lens 23.

Table 6 However, it is assumed that the shape of the aspherical surface is expressed by the same formula as in the embodiment described above.

The photographing lenses 20 shown in Tables 5 and 6 have almost the same effects as those of the above-mentioned embodiments, and in particular, aberrations such as spherical aberration, astigmatism, and distortion are reduced as shown in FIGS. 6(A) to 6. Since the curve is as shown in (C), it can be seen that the aberration correction has been performed well.

Note that the present invention is not limited to each of the above-mentioned embodiments.
A combination of the embodiments may also be used. In this case as well, if the image side surface of the first plastic lens, the object side surface of the plastic lens immediately before the glass lens, and the image side surface of the last plastic lens are formed into aspherical surfaces, Aberration correction can be effectively performed.

[Effects of the Invention] As explained in detail above, according to the present invention, a plurality of plastic lenses and one glass lens are provided, and only the glass lens has an imaging function, and the plurality of plastic lenses The entire front group can be configured into an almost afocal optical system, or the front group plastic lens can be configured into an almost afocal optical system with the glass lens as the boundary, and the object side of the rear group plastic lens can be configured with a glass lens. By forming the curved surface so that the incident angle of the emitted light ray is almost perpendicular, performance deterioration due to temperature changes can be prevented, and a high-performance product can be obtained at low cost.

In this case, if the image side surface of at least one plastic lens is formed into an aspherical surface, aberrations such as distortion can be effectively corrected.

[Brief explanation of drawings]

1 and 2 show a first embodiment of the present invention, FIG. 1 is a diagram showing the schematic structure of the photographic lens, and FIG.
) to (C) are diagrams showing the aberration curves, Figures 3 and 4.
The figure shows the second embodiment, FIG. 3 is a diagram showing the schematic configuration of the photographing lens, FIGS. 4(A) to (C) are diagrams showing its aberration curve, and FIGS. 3 examples are shown, and the fifth example
The figure shows the schematic structure of the photographic lens, Fig. 6 (A)
~(C) is a diagram showing the aberration curve. 1.10.20...Photography lens, 2~4°11
~14.22.23...Plastic lens,
5.15.21...Glass lens, RA2RB
2... Image side of the first plastic lens,
RAs...Object side of the plastic lens immediately after the glass lens, RBe...Object side of the plastic lens just before the glass lens, RC6...
Image side of the rearmost plastic lens. can be done. RA+ RA2 A3 RA4RA5 Tomoe A6 RA7 RA8RA9 yen start A1 Fig. - LINE I [F] Balance fraud loss left 〒Nai 7 Bokuin ('/,) (A) (B) C) Fig. - uNE〕Sense (゛Faced 7i lacquered three vinegar giant, four-layered Te'4゛stony diagram Figure 01 +Q1 1 -01 5 +5 Bead beveled series and aberration Keikoku IB also (2) (B) (C) Figure

Claims (5)

[Claims] (1) A plurality of plastic lenses arranged on the optical axis, and a lens arranged between the plurality of plastic lenses.
glass lenses, only the glass lenses have an imaging function, and with the glass lenses as a boundary, the plastic lenses in the front group are constructed into an almost afocal optical system, and the plastic lenses in the rear group are configured to form an almost afocal optical system. A photographic lens characterized in that an object side surface of the glass lens is formed into a curved surface such that an incident angle of a ray of light emitted from the glass lens is substantially perpendicular. (2) In claim 1, at least one of the front group
A photographic lens characterized in that the image side surface of the second plastic lens is formed into an aspherical surface. (3) It is equipped with a plurality of plastic lenses and one glass lens, and only this glass lens has an imaging function,
A photographic lens characterized in that all of the plurality of plastic lenses are configured into a substantially afocal optical system. (4) In claim 3, all of the plurality of plastic lenses are arranged in a front group of the glass lens, and the image side surface of at least the first plastic lens and the object of the plastic lens immediately in front of the glass lens. A photographic lens characterized by having an aspherical side surface. (5) The photographing lens according to claim 3, wherein all of the plurality of plastic lenses are arranged in a rear group of the glass lenses, and the image side surface of at least the rearmost plastic lens is formed into an aspherical surface. .