JPS587971B2 - Great lens - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to improvements in large-diameter, wide-angle Fourier transform lenses.

In general, a Fourier transform hologram is produced by placing a transparent object Sx4 at the position of the first focal plane Fx1 of the Fourier transform lens Lx, illuminating it from the left side, as shown in FIG. A hologram SX2 is created by recording the object beam together with the reference beam Tx at a nearby point.

When obtaining the reproduced image S'X2 from the hologram SX2 created in this way, if this hologram SX2 is placed at the same position as at the time of recording, as shown by the chain line, the same Fourier transform lens Lx as at the time of recording is used. However, as shown in Fig. 2, if the created hologram Sx2 is located at a position far from the optical axis or along the optical axis of the Fourier transform lens L'x for reproduction, it may be different from the position at the time of recording. If the Fourier transform lens L'x for reproduction is placed in a position where the F number is small and bright, and the reproduction image S
Since 'x2 becomes large, a lens with a large angle of view is required.

Furthermore, since the lens is a Fourier transform lens L'x, when the angle of view is θ, the ideal image height must be given by fsinθ instead of ftanθ.

An object of the present invention is to provide a large-diameter, wide-angle Fourier transform lens that satisfies the above-mentioned requirements. The group is a meniscus-shaped diverging single lens with the concave surface facing the object side, and the second group is a meniscus-shaped converging single lens with the concave surface facing the object side, or two lenses, the third and fourth groups. group, and the fifth group are convergent single lenses, and the sixth group is a convergent single lens.
The group consists of a meniscus-shaped converging single lens with a convex surface facing the object side, or two lenses, and the seventh group is a meniscus-shaped reversing single lens with a convex surface facing the object side, and f total Focal length of the system R1F Radius of curvature of the front surface of the first group lens R7F Radius of curvature of the rear surface of the seventh group lens t1.2 When the axial thickness from the front surface of the first group lens to the rear surface of the second group lens is (1) -0.7f<R1F<-0.5f (2) 0.4f<R7F<0.6f (3) 0.35f<t1.2<0.7f and the angle of view When θ, the ideal height is f
The feature is that it is given by f sin θ instead of tan θ.

In short, since the present invention relates to a large-diameter, wide-angle Fourier transform lens, a lens with a front diaphragm is designed.

Although it is usually extremely difficult to obtain an optical system with a large-diameter wide-angle lens with a front diaphragm without vignetting in the amount of peripheral light,
In the present invention, by a lens configuration in which diverging lenses with concave surfaces facing outward are arranged at both ends, and several groups of converging lenses are arranged between these diverging lenses,
This made it possible for the first time to create a lens system with no vignetting in the amount of peripheral light, even with a front diaphragm and a large aperture wide-angle lens.

In addition, since the lens system of the present invention has meniscus-shaped diverging lenses with concave surfaces facing outward at both ends, the influence of the refractive surfaces of each of these diverging lenses on the light rays is small. This makes it easy to correct aberrations, which is advantageous.

Furthermore, in the lens system of the present invention, since five groups of convergent lenses are arranged between the divergent lenses at both ends, the influence of each convergent lens on aberrations can be reduced. A lens system without vignetting in the amount of peripheral light can be obtained.

Next, the necessity of each condition will be explained in detail.

Conditions 1 and 2 are necessary to maintain the Petz Parr sum at an appropriate value, suppress an increase in astigmatism, and prevent the occurrence of coma flare.

First, when the radius of curvature R1F of the front surface of the first group lens becomes larger than the upper limit of condition 1 (it becomes smaller in absolute value), the Petzupard sum becomes too small and as the sagittal image plane approaches the maximum angle of view, it becomes larger in one direction. , the sasicle image plane and meridional image plane become unbalanced,
Astigmatism becomes large.

In addition, since the radius of curvature R1F of the front surface of the first group lens has become stronger, the upper peripheral light beam is strongly influenced by this surface, causing excessive coma flare and deteriorating coma aberration.

Therefore, if the refractive index of the convex lens is reduced in an attempt to set the Petzupar sum to an appropriate value, the radius of curvature of the convex lens becomes stronger, causing coma flare, further deteriorating coma aberration, and making correction difficult.

Therefore, conversely, when R1F becomes smaller than the lower limit of Condition 1 (it becomes larger in absolute value), the Petzupard sum becomes larger, and as a result, the curvature of field becomes larger and astigmatism becomes larger.

Furthermore, as the concave surface of the first surface becomes looser, the upper peripheral light beam is less affected by this surface, so that under coma flare occurs and coma aberration deteriorates.

Next, when the radius of curvature R7F of the rear surface of the seventh group lens becomes larger than the upper limit of condition 2, the same phenomenon as when R1F becomes smaller than the lower limit of condition 1 is induced, and conversely R
When 7F is smaller than the lower limit of conditional expression 2, the same phenomenon as when R1F is larger than the upper limit of condition 1 occurs.

Furthermore, condition 3 is necessary to keep spherical aberration at an appropriate level and to suppress the increase in extraordinary aberrations.

Now, if the axial thickness t1.2 from the front surface of the first group lens to the rear surface of the second group lens becomes larger than the upper limit of condition 3, the spherical aberration becomes under and the image plane also becomes over.
Astigmatism becomes large.

If we attempt to correct this by increasing the curvature of the convex lens or decreasing the curvature of the concave lens, coma flare will occur and coma aberration will deteriorate, making correction extremely difficult.

On the other hand, if t1.2 is made smaller than the lower limit of condition 3, a phenomenon opposite to that of making it larger than the upper limit will be induced.

Examples of the large-diameter, wide-angle Fourier transform lens according to the present invention will be shown below.

Example ■ In this Example I, the focal length f is f = 100, the F number is F = 2.0, the angle of view is 2θ = 3730', the standard design wavelength is λ = 632.8 mμ, and the aperture is The design is such that a cover glass G is placed behind the lens at one focal point, and this is shown as a longitudinal section as a in Figure 3. In the figure, the radius of curvature of each lens surface is d
〃 〃 Surface spacing n 〃 Expressed as the refractive index of each lens at wavelength λ = 632.8 mμ, it is as follows. In Fig. 4, a indicates the spherical aberration and sine condition, b indicates the astigmatism, and C represents distortion aberration, and d represents lateral aberration.

However, for distortion, when the angle of view is θ, the ideal image height is f
It is calculated as sin θ.

Example■ In this example, the focal length f is f=100, the F number is F=1.65, the angle of view is 2θ=37°30', the standard design wavelength is λ=632.8mμ, the aperture position, The position of the cover glass G was designed to be the same as in Example I.
This is shown as a longitudinal section as b in Figure 3. In the figure, R is the radius of curvature of each lens surface, d, in order from the object side.
〃 〃 Surface spacing n In order from the object side, the wavelength λ of each lens = 632.8 m
Expressed as a refractive index in μ, it is as follows: In FIG. 5, a indicates the spherical aberration and the sine condition, b indicates the astigmatism, c indicates the distortion, and d indicates the lateral aberration.

[Brief explanation of the drawing]

Figure 1 is a layout diagram when creating a Fourier transform hologram, Figure 2 is a layout diagram when reproducing a Fourier transform hologram, and Figures a and b are longitudinal sectional front views of Embodiment I and Example II according to the present invention. As shown in FIG. 4, a, b, c, and d are aberration diagrams of Example 2, and a, b, c, and d of FIG. 5 are aberration diagrams of Example 2. Lx...Fourier transform lens, L'x...
・・Fourier transform lens for reproduction, FX15 FX1・・
...First focal plane, Fx2, F'x2... Second focal plane, Tx... Reference light flux, T'x...
...Reference light beam for reproduction, Sx1... Transparent object, S
x2...Fourier transform hologram, S'x2.
...Reproduced image, L1...First group, L2...
...2nd group, L3...3rd group, L4...
...4th group, L5...5th group, L6...
...6th group, L7...7th group, d1 to d17.
... Lens thickness or air gap on the optical axis, R1 to R18 ... Radius of curvature of lens refractive surface, F1 ... First focal plane, F2 ... ...Second
focal plane.

Claims (1)

[Claims] 1. Viewed in order from the object side, the first group is a meniscus-shaped diverging single lens with a concave surface facing the object side, and the second group is a meniscus-shaped convergent lens with a concave surface facing the object side. A single lens or two lenses, the third, fourth, and fifth groups are convergent single lenses, and the sixth group is a meniscus convergent single lens with a convex surface facing the object side, or Two lenses, the 7th group consists of 7 elements in 7 groups or 9 elements in 7 groups of a meniscus-shaped diverging single lens with a convex surface facing the object side, f
Focal length of the entire system R1F Radius of curvature of the front surface of the 1st group lens R7F Radius of curvature of the rear surface of the 7th group lens t1, 2 When the axial thickness from the front surface of the 1st group lens to the rear surface of the 2nd group lens is ( 1) −0.7f<R1F<−0.5f (2) 0.4f<R7F<0.6f (3) 0.35f<t1.2<0.7f and set the face angle to θ When the ideal height is f
A large-diameter wide-angle Fourier transform lens characterized by being given by f sin θ instead of tan θ.