JPS5965819A - Fundus camera - Google Patents

Abstract

PURPOSE:To use a simple conversion equation and obtain correct distance, by providing an optical image formation system with such negative distortion that a direct projection image is formed. CONSTITUTION:The optical image formation system consists of an objective and a relay lens. The objective 6 consists of a negative-positive cemented biconvex lens, and the relay lens consists of the 1st group of a negative-positive cemented negative lens, the 2nd group of a positive lens, the 3rd group of a negative meniscus lens, and the 4th group of a negative-positive cemented positive lens. Consequently, the optical image formation system is almost a direct projection image type optical image formation system. which has negative distortion. Consequently, correct distance is known by using the simple calculation equation.

Description

[Detailed description of the invention] The present invention relates to a fundus camera.

A fundus camera is well known and has a configuration as shown in FIG. 1, for example. 1, a ring slit 3. with an annular opening 3a placed approximately conjugate with the lamp 1 with respect to the lamp 1, the condenser lens 2, and the condenser lens 2. Projection lens 4. With respect to the projection lens 4, a perforated mirror 5 having a central opening 5a obliquely arranged at a position substantially conjugate with the ring slit 3 constitutes an illumination system. On the other hand, the objective lens 6, the aperture diaphragm 7, the relay lens 8, the movable mirror 9, the reflector 10, the field diaphragm] 1, the eyepiece 12, the field diaphragm parfocality 11, and the film 13 placed in the frame 4 are observed. It makes up the shooting system.

When observing the fundus 14a of the eye 14 to be examined, first the light beam emitted from the rung 1 is passed through the ring slit 3 by the condenser lens 2.
After the light is focused nearby and the center is shielded, the projection lens 4
The light is again focused near the perforated mirror 5. This light beam is further reflected by the perforated mirror 5, and then forms an image of the ring slit 1-3 near the iris 14b of the subject's eye 4 by the objective lens 6, and then illuminates the fundus 14a. The light reflected by the fundus 14a forms a -a fundus image Q in front of the perforated mirror 5 by the objective lens 6. After passing through the aperture diaphragm 7, this fundus image Q is relayed by a relay lens 8, passes through a movable mirror 9 and a reflecting mirror 10, is re-imaged at the position of a field diaphragm 11, and is observed through an eyepiece lens 12. Furthermore, in recent years, a type called a non-mydriatic type that uses infrared light when observing the fundus has become known, but observation with the naked eye is not possible with this type. For this reason, it is also possible to move the reflection value 10 out of the optical path as shown by the broken line in the figure, form the fundus image on the imaging surface of the image pickup tube 15 such as a vidicon, and display the fundus image on the TV monitor 16 for observation. It is being done. Here, when the movable mirror 9 is flipped up as shown by the broken line, the fundus image Q is re-imaged on the film 130, and a fundus photograph can be taken.

In addition, usually the surface of the objective lens or the anterior segment of the eye to be examined (
The illumination system, observation,
Although a sunspot and an aperture diaphragm are provided in the photographing system, explanations regarding these will be omitted.

In this way, photographs obtained with a fundus camera and images displayed on a TV monitor correspond to figures obtained by projecting the curved fundus onto a flat film or imaging surface, but it is well known that When projecting a curved surface onto a plane, as shown in Figure 3, if one of angle, length, and area is accurately projected, the other two will be inaccurate. Therefore, for example, the distribution of blood vessels and lesions in the fundus can be accurately determined based on a photograph of the fundus.
When determining the fill or creating a fundus map,
It is necessary to convert the distance that can only be measured on the photo into an actual value. However, in photographs obtained with a conventional fundus camera, this conversion is extremely complicated.

Until now, all imaging optical systems consisting of objective lenses, relay lenses, etc. for forming fundus images on image receiving means such as film and image pickup tubes have been corrected for aberrations to minimize distortion. . However, the photographs obtained with such an optical system are similar to the images of the fundus projected onto a flat surface using stereoscopic mapping, which is known for the production of maps, and although the angles are reproduced fairly accurately, Length and area are inaccurate, and the length conversion formula is troublesome. Literature (Journal of Japan Direct Optics Society vol. 3 No. 1 1982
) is an example of the conversion method given in the fundus photographic film. .3 m
It uses a complicated conversion formula that determines the angle at which light rays from two points m apart are placed behind the objective lens of the fundus camera. Furthermore, with this method, in order to determine the distance from the center of the fundus photograph, W must be integrated with respect to V, making the conversion even more complicated.

In view of the paper, it is an object of the present invention to provide a fundus camera that can determine the correct distance using a simple conversion formula.

That is, the present invention provides a fundus camera equipped with an imaging optical system that forms a fundus image on an image receiving means such as a film or an image pickup tube. The above objective is achieved by generating distortion.

Hereinafter, the present invention will be described in detail with reference to the drawings.

14a is projected onto the film 13 with a light beam parallel to the optical axis AK. The fundus of the eye can usually be approximated fairly well by a spherical surface, so if its radius of curvature is r and the angle subtended by the minute distance ds is dθ, then dsllcns(J, = cls') can be immediately obtained. To find the correct thickness, simply divide the measured value in photo 2 by CO3θ1, which is a very simple conversion.Also, measure the distance from the light i'Qt+ to any imaginary point on the photo. If the value l/ is IH, then the following relationship holds true: ds = rdθ, so 1f - t'ds' = 1cosθ r (1θ = rsin
θl θ1=5In-'-EL The actual size corresponding to Ij is 1. = rθ1, so L
= r 5in-' -u-・・・・・・・・・・・・
... (3) allows finding the correct distance on the fundus. When the projection magnification is β, equation (3) is naturally L' L = r 5ln-'W...
・(It becomes 3 wa.

Comparing equation (2), (31 or (3)) with equation (1) above, it can be seen that the image forming optical system has an imaging optical system with negative distortion that gives a direct image.
It can be seen that the actual size value can be obtained very easily based on the photograph taken by the a camera.

Here, the distortion that should be imparted to the imaging optical system of the present invention will be explained in detail.

Figure No. 3 is a schematic cross-section along the optical axis of the human eye. As shown in the figure, point P at a height of 11' on the fundus and aperture A
(Figure 1 shows the image taken by the 5th Kero aperture 70 objective lens)
Let the angles that the principal ray 1 passing through the center of the eye make with the optical axis inside and outside the eye be α' and α, respectively, and the angle of incidence and exit angle of the principal ray 1 on the corneal surface be 1' and i, respectively.

In addition, the radius of curvature of the corneal surface and the fundus are respectively ㇠l, Tt2,
The angle between the optical axis and the straight line connecting the center of curvature O of the fundus and the point P is r/, the distance between the aperture A and the corneal vertex is Dl, and the total length of the eye is D
Let it be l. Further, it is assumed that - is the refractive index within the eye, and f is the focal length of the imaging optical system.

When there is no distortion in the imaging optical system, the image height of point P formed on the film surface is h=ftanα ・・・・・・・・・・・・・・・・・・
- (4). On the other hand, if the magnification is 1, the image height obtained by the type projection imaging system is exactly h'. Therefore, the distortion aberration to be imparted to the imaging optical system of the present invention is calculated by dividing the magnification correction coefficient by I (1 = (K''--1) x 100 (H)... - (5
)h′. This is expressed as a function of the angle of view α.

In FIG. 3, 5in i'-kM sin cl 1. --(6
)1.1 sin i = n sin i'・・・・・・・・・
・・・・・・・・・(7)α=α'+i'-i
...... Old ...... (8111' =
R, 2 sin r' Here, 1) as the standard value of 1lffl for person 11R
+ = 3.6 1)2 = 241(・+ =
7.7 When R2= 11.6n=1.4, Equations (6) and (7) respectively become Sin i'=
0.5325 sin a' - old mountain (6 sin i = -0,7455 sin a' -
-(73), and by substituting these values, formula (8) becomes a = a'+5in-'(-0fi325 sin
a') -51n-'(-0,7455sin α')・
・・・・・・・・・(8 are obtained, but this (81
The formula is -75〈α'〈 within the range of 75 degrees, α = 1213α' ......Mountain ・
・・・・・・・・・・・・ (Ft”)X100r%j・
・・・・・・・・・・・・・・・Mountain...(55 is obtained. Since ts-+0 when distribution → 0, K= f
/IJ5R2o・・・・・・・・・・・・・・・・・・・・・・
(ri) That is, an imaging optical system having a negative distortion aberration expressed by the following five equations forms a direct image of the fundus of the eye to be examined.

Next, FIG. 4 shows a specific example of an imaging optical system having the above-mentioned distortion aberration. In the figures, the same parts as in Figure 1 are given the same numbers, but in this example, the imaging optical system is composed of an objective lens and a relay lens. Objective lens 6
consists of a negative and positive cemented biconvex lens, and relay 1/lens c1
It consists of a first group of negative-positive cemented negative lenses, a second group of positive lenses, a third group of negative meniscus lenses, and a fourth group of negative-positive cemented positive lenses. The numerical values of each parameter are as follows:F 1 rl=2.3456 dI=0.2165 n+=1.72825
v1 = 28.46r2 = 1.3961 dz = 1.3725 +12 = 1.58
9i3 shi2=61.11r 3=1
．． 3583 d3 = 6.2069 r4 = ω (aperture) (L = 0.0541 r5 = -0,7115 ds = 0.0945 n3 = 1.72
L'3 = 50.25re, = 0.268
4 da = 0.0985 n4 = 1.7282
5 4'4 = 28.46rt=0.7174 d7= 0.1999 rs= 1.3062 ds = 0.1804 05 = 1.72
1's = 50.25rQ = 1
．． 1979 ds=0.2367 rlQ=1.0176 dlo=0.1252 n6=1.69895
Shiro =: (Q, 32r11 = 0.7542 dn = 0.3306 r 12 = -7,6626 d+z = 0.1371 ny = 172825
1'? =28.46r13=0.8315 d13=0.367 n8=1.713
4's = 53.89r 14=-1,19
94 However, F is the composite focal length of the entire system, ri is the radius of curvature of each lens surface, and di is the th! The distance between the surface and the (i+1)th surface, ni is the refractive index of each lens, and ν1 is the Abbe number of each lens.

The aberrations of this optical system are as shown in FIG. 5, and the distortion aberration (theory obtained from the five equations) From this table, it can be seen that the above numerical examples are almost the same as for the installed shadow imaging optical system.

[Brief explanation of drawings]

Figure 1 is a diagram showing the outline of a conventional fundus camera, Figure 2 is a diagram to explain the length conversion formula in the stationary projection method, and Figure 3 is a diagram showing the outline of a conventional fundus camera.
The figure is a cross-sectional view of a human eye to explain the distortion aberration of the present invention.
FIG. 4 is a sectional view of one embodiment of the imaging optical system of the present invention, and FIG.
The figure is an aberration diagram of the embodiment shown in FIG. 4. Figure 5-98- Distortion aberration IH0,41 4%) Senji correction book Showa! 57', RF Special V1 Application No. 17E568]2,
Name of the invention lff, I bottom camera 3, auxiliary if 2 coin case ('1 Which relationship Special f11 Applicant 〒151 bundle 9 Hatagaya 2-chome, Shibuya-ku, Tokyo/13-2-4, Amendment order No. 11 Self-sealed 5 , Detailed explanation column 6 for the specification to be amended, contents of the amendment (1) r +; = -1,
3583-1 is r 13-1, 3583
(Aspherical surface)” is supplementary i1. (2) Insert the following sentence between lines 1011 and 11 on page 12. ``In addition, the image side of the Ri-J object 6 is illuminated with the 111 point as the origin. In the axial direction is the Z axis (direction of light progression Ij or positive), and on the surface 1 corner perpendicular to this,
C--0,26'Gx 40 [= 0,
1flix To-51-(1,B7x 1O-8G-
0,2! +2X To-” If = O, +0
11x 1f)-”.J

Claims (1)

[Claims] A fundus camera comprising an imaging optical system for forming a fundus image of an eye to be examined on an image receiving means, characterized in that the imaging optical system has a negative distortion aberration so as to form a placed image.