JPH0422572B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a variable-magnification fundus camera, and more particularly to a variable-magnification fundus camera that can always obtain a constant film exposure amount even when the variable-magnification lens of an observation photographing system is varied. In the case of a conventional variable-magnification fundus camera, a variable-magnification lens is provided in the observation photographing system to change the magnification, and the photographing aperture of the observation-photographing system is changed in conjunction with the variable magnification operation of the variable-magnification lens. In this way, even when the amount of illumination light from the fundus illumination system is constant, there is a device that always keeps the amount of film exposure constant and eliminates fluctuations in the brightness of the screen. However, with such conventional variable-magnification fundus cameras, when the variable-magnification lens is operated to increase the magnification, the photographic aperture is increased to keep the film exposure constant. As the magnification of a variable magnification lens increases, the aperture becomes larger and the depth of field gradually becomes shallower, so when photographing an uneven fundus, only part of the fundus is in focus at high magnification. The problem was that there were practical difficulties. In addition, in the case of another conventional fundus camera capable of variable magnification, a variable magnification lens is provided in the observation photographing system to change the magnification, and the illumination of the fundus illumination system is linked to the variable magnification operation of the variable magnification lens. There has been a system in which the amount of light is varied so that even when the aperture of the photographing diaphragm of an observation photographing system is constant, the amount of film exposure is always constant and fluctuations in the brightness of the screen are eliminated. However, in conventional variable-magnification retinal cameras like this, when the variable-magnification lens is operated to increase the magnification, the amount of illumination light is increased to keep the film exposure constant. As the magnification of the variable magnification lens increases, the amount of illumination light gradually increases. The amount of increase is, for example, assuming that the variable magnification of the variable magnification lens, that is, the imaging magnification, is variable from βmin to βi to βmax, and if the illumination light amount of the light source, for example, an illumination light source, at βmin is 1, then at βi, it is β/βmin ² It increases by the value of , resulting in a rapid increase. Therefore, the illuminance of the fundus of the subject's eye becomes extremely large when the magnification is high, and although it is difficult for the subject to withstand the glare even under normal circumstances, the condition worsens and the condition worsens, resulting in tearing. This causes problems such as leakage and increased blinking, resulting in poor operability during shooting. Furthermore, a large-capacity light source is required, resulting in the problem that the entire device becomes expensive. This invention has been made in view of these conventional problems, and involves changing the photographing aperture of the observation photographing system in response to changes in the lower magnification of the variable magnification lens provided in the observation photographing system. The object of the present invention is to solve the above-mentioned problems by varying the amount of illumination light from the fundus illumination system in response to changes in the high magnification side and keeping the amount of film exposure constant. The present invention will be explained below based on the drawings. 1 to 6 are diagrams showing one embodiment of the present invention. In the figure, reference numeral 1 is an objective lens placed facing the fundus Ef of the eye E to be examined.
A perforated mirror 3 is obliquely provided on the optical axis 2 of the eye E at a position substantially conjugate with the pupil of the eye E with respect to the objective lens 1. The illumination optical system includes an illumination optical system 4 which is an incandescent lamp.
and a photographing light source 5 which is a xenon tube, and the light from the illumination light source 4 is once converged onto the photographing light source 5 by a first condenser lens 6, and then diverged to a second condenser lens 7. The light enters, passes through the ring-shaped diaphragm 8, is reflected by the mirror 9, passes through the relay lenses 10 and 11, is reflected by the perforated mirror 3 toward the objective lens 1, passes through the objective lens 1, and passes through the pupil of the eye E to be examined. Projected onto the fundus Ef. After the light from the photographic light source 5 enters the second condenser lens 7, it follows the same optical path as the photographic light source 5 and reaches the fundus.
Projected to Ef. On the other hand, the observation photographing system includes a photographing diaphragm 1 with a variable aperture, which is provided behind the perforated mirror 3 at a position approximately conjugate with the pupil of the eye E with respect to the objective lens 1.
2, a focusing lens 13 and a variable magnification lens 1 provided sequentially along the photographing optical axis 2a behind the photographing aperture 12.
4 and an imaging lens 15, the reflected light from the fundus Ef passes through a photographic aperture 12, a focusing lens 13, and a variable magnification lens 14, and is imaged by the imaging lens 15 on a photographic film surface 16. A flip-up mirror 17 is disposed in front of the photographic film surface 16, and when the mirror 17 is in the illustrated position, the light from the imaging lens 15 is reflected by the mirror 17, and an image is formed on _the focal plane fa. , the field lens 18 , the prism 19 and the eyepiece 20 . Next, the variable power lens 14 will be explained in detail. As shown in FIG. 2, the variable magnification lens 14 is mounted on a rotating disk 22 that is mounted on a rotating shaft 21. As shown in FIG. The variable magnification lens 14 is a low-magnification lens with a wide angle of 45°.
It is composed of a lens 14a with a wide angle of 30°, a lens 14b with a wide angle of 30°, and a lens 14c with a narrow angle of 20° and a lens 14d with a narrow angle of 15° on the high magnification side, and each of these lenses 14a to 14d is mounted on a rotating disk 22. They are attached in a circular pattern at equal intervals. The rotating shaft 21 has bearings 23, 2 attached at both ends to a fundus camera housing (not shown).
4, and a bevel gear 25 is fixed to one end. An operating shaft 26 is meshed with this bevel gear 25, and the operating shaft 26 is rotated by a variable-magnification operating handle (not shown). Therefore, the operation shaft 26 is rotated by rotating the variable power operation handle.
rotates, drives the bevel gear 25, and rotates the rotating shaft 2.
By rotating the rotating disk 22 together with 1,
Any lens 14a to 14d among the variable magnification lenses 14 mounted on the rotating disk 22 can be inserted into the photographing optical axis 2a of the observation photographing system. In the variable magnification lens 14 of this embodiment, the lens 1 is located on the photographing optical axis 2a.
4a to 14d are selectively inserted, but the present invention is not limited to this, and the magnification may be changed by changing the imaging lens or by using a zoom method. Of course it's a good thing. Furthermore, the photographing diaphragm 12 whose aperture can be varied will be explained. A diaphragm plate 30 constituting the photographic diaphragm 12 is attached to the rotating shaft 21, and the diaphragm plate 30 has aperture holes 12a, 12b, 12c, and 12d having different aperture degrees.
is formed. That is, the openings of the aperture holes 12a and 12b corresponding to the lenses 14a and 14b on the low magnification side of the variable magnification lens 14 are formed in a size such that the brightness of the photographing system is equal, and Corresponding aperture hole 12c,
The aperture 12d is formed to have the same size as the aperture of the aperture hole 12b corresponding to each lens 14b having an angle of 30° on the low magnification side. The rotating shaft 21 on which the photographing aperture 12 and the rotating disk 22 of the variable magnification lens 14 are mounted is configured to vary the photographic aperture in response to changes in the lower magnification of the variable magnification lens, and Aperture interlocking means is configured to keep the photographing aperture constant in response to side changes. Therefore, when an arbitrary lens among the variable magnification lenses 14, for example, the lens 14a, is inserted into the photographing optical axis 2a of the observation photographing system, the aperture plate 30 also rotates in conjunction with the rotation of the rotating disk 22. The lens 14a
An aperture hole 12a having an aperture value corresponding to the aperture value is inserted into the photographing optical axis 2a of the observation photographing system. Finally, a configuration for varying the amount of illumination light from the illumination light source 4 and photographing light source 5 will be described. As shown in FIG. 1, the rotary shaft 21 is provided with a switching switch S for a photographing light source 5 which switches in three stages as the variable magnification lens 14 changes magnification, and a switch S for a photographic light source 5 that switches to three stages as the variable magnification lens 14 changes magnification.
An illumination variable resistor R _T whose resistance value changes for the illumination light source 4 in response to the magnification change of the illumination light source 4 is provided. The changeover switch S is provided in the electric circuit shown in FIG. 5, which changes the amount of light emitted from the photographing light source 5 by changing the capacitance of the capacitor. This electric circuit connects three capacitors C ₁ , C ₂ , C ₃ with different capacities in series to the power source E ₁ via a changeover switch S, and connects them in series _.
A photographing light source 5, for example, a xenon tube, is connected in series to the camera. When the variable magnification lens 14 is variable and the lower magnification lenses 14a and 14b are used, the switching switch S is set to the condenser.
When the high-magnification lens _14c is used, the switch S is connected to the condenser _C2 , and when the high-magnification lens 14d is used, the switch S is connected to the condenser C2.
Light source 5 for photography is connected to C ₃ in a switching manner.
emits a selected amount of light. Note that the photographing light source 5 emits light only when a trigger switch (not shown) is turned on. In this case, each lens 14a~ of the variable power lens 14
The brightness (F number) ratio of 14d is 1:1:
The ratio is 1.52:2.05, and it becomes darker on the high magnification side.
Therefore, in order to keep the amount of film exposure constant, the capacitors C ₁ to C ₃ are adjusted so that the amount of light from the photographing light source 5 to each lens 14a to 14d is increased at a ratio of 1:1:1.52 ² :2.05 ² . Set the capacity. Further, the variable resistor R _T for illumination is provided in the electric circuit shown in FIG. 6, which changes the amount of light emitted from the illumination light source 4 by changing the resistance value. This electrical circuit connects the power source E ₂ to the lighting light source 4.
For example, it is constructed by connecting an incandescent lamp and a lighting variable resistor R _T in series. In this case, similarly to the above, the variable resistor R _T is switched to three resistance values corresponding to the variable magnification of each lens 14a to 14d in the variable magnification lens 14, and the illumination is performed so that the film exposure amount is constant. The light source 4 emits a selected amount of light. Note that a variable transmittance filter may be arranged in the illumination system to change the amount of illumination light to the fundus without changing the brightness of the light source itself. Next, the effect will be explained. First, when the operating shaft 26 is rotated by rotating a variable power operating handle (not shown), the bevel gear 25 is driven and the rotating disk 22 is rotated together with the rotating shaft 21 . The variable magnification lens 14 attached to the rotary disk 22 is also displaced, and when the low magnification lens 14a with a wide angle of 45° among the variable magnification lenses 14 is inserted into the photographing optical axis 2a of the observation photographing system, the variable magnification lens 14 is also displaced. Stops the rotation operation of the double operation handle. In this way, lens 1
4a is set as the photographing optical axis 2a of the observation photographing system.
At the same time, the aperture plate 30 provided on the rotating shaft 21 also rotates, and an aperture hole 12a having an aperture value corresponding to the lens 14a of the photographing aperture 12 is inserted in conjunction with the photographing optical axis 2a of the observation photographing system. At this time, the switching switch S and the lighting variable resistor R _T provided on the rotating shaft 21 are connected to the rotating shaft 21.
The switching switch S is switched to the capacitor _C1 , and the lighting variable resistor R _T is switched to a resistance value corresponding to the lens 14a. Thereafter, the variable magnification operation handle is rotated to change the variable magnification lens 14 from the low magnification side lens 14b and the low magnification side lenses 14a, 14b to the high magnification side lens 14c,
14d, the photographic aperture 12 corresponds to each of the lenses 14b to 14d whose magnifications have been changed.
are also variable to the corresponding aperture holes 12b to 12d, respectively, and the switching switch S and the lighting variable resistor R _T
The capacitors C ₂ and C ₃ and resistance values are also switched to correspond to the respective lenses 14b to 14d. Next, the difference in operation between the conventional example and this embodiment will be explained based on the graphs shown in FIGS. 7 to 12 and the table shown below.

[Table] In the table, A shows a conventional fundus camera in which the photographing aperture is varied as the magnification of the variable magnification lens changes, and B shows another conventional fundus camera in which the light intensity is varied in response to the variable magnification of the variable magnification lens. C indicates the fundus camera of the present invention, 2α is the angle of view of the variable magnification lens of each fundus camera, f is the focal length of the variable magnification lens, and β
is the photographing magnification, F is the F number, λ is the wavelength used, and X
indicates depth of field. (X=2F ² λ/β ² ) This chart shows the values shown in FIGS. 7 to 12 numerically for comparison.

[Table] The table summarizes numerical examples in the embodiments of this invention. Note that the ratio is based on the case where the angle of view is 45°. Figure 7 shows the change in depth of field when the photographic aperture is varied and the film exposure is kept constant using a conventional fundus camera. Figure 8 shows the change in the illumination light ratio of the illumination light source. Figure 9 shows the change in depth of field when the amount of illumination light from the illumination light source is varied and the amount of film exposure is kept constant using a conventional fundus camera.
Figure 0 shows the change in the illumination light ratio of the illumination light source, and the first
Figure 1 shows the change in depth of field when the film exposure amount is kept constant by varying the photographing aperture and the illumination light amount of the illumination light source in the fundus camera of the present invention.
The figures each show changes in the illumination light ratio of the illumination light source. In FIGS. 7, 9, and 11, the vertical axis X indicates the depth of field, the horizontal axis f indicates the focal length of the variable magnification lens, and β indicates the photographing magnification. Also, Figures 8 and 10
The vertical axis Y in the figures and FIG. 12 indicates the illumination light ratio, and the horizontal axes f and β are the same as described above. Note that the photographing magnification β is determined by each lens 14a to 1 of the variable magnification lens 14 used.
The magnification is 4d, and each lens 14a to 14d is represented by an angle of view. It is assumed that the conventional example also uses the same variable magnification lens 14 as that of the present invention. As is clear from FIGS. 7 and 8, in a conventional fundus camera, when the illumination light amount of the illumination light source 4 is kept constant and the photographing diaphragm 12 is varied in accordance with the magnification change of the variable magnification lens 14, the subject As shown in the depth of field curve _D1 in FIG. 7, the depth of field gradually becomes shallower as the variable power lens 14 is changed from the lower magnification lens 14a to the higher magnification lens 14d. I understand. On the other hand, it can be seen that the illumination light ratio curve _L1 is a constant horizontal straight line. Note that the illumination light ratio at this time is based on the illumination light when the low magnification lens 14a is used. Next, as is clear from FIGS. 9 and 10,
In another conventional fundus camera, when the aperture of the imaging diaphragm 12 is kept constant and the illumination light intensity of the illumination light source 4 is varied in accordance with the variable power of the variable magnification lens 14, the depth of field is as shown in FIG. As seen in the depth of field curve D ₂ ,
It can be seen that even when the variable magnification lens 14 is changed from a high magnification lens 14a to a high magnification lens 14d, it remains a constant horizontal straight line and does not change. On the other hand, the illumination light ratio curve L ₂ is rising, indicating that the amount of illumination light from the illumination light source 4 increases rapidly as the magnification of the variable power lens 14 is changed from low to high magnification. Ru. On the other hand, when the variable magnification lens 14 is changed from the low-magnification lens 14a to the high-magnification lens 14d in the fundus camera of the present invention, from the low-magnification lens 14a to the low-magnification lens 14b. When the magnification is changed to
2b, the aperture value, or aperture, increases from small to large, and the depth of field becomes shallow. As shown in FIG. 11, the portion of the depth of field curve _D3 from lens 14a to lens 14b is downward, indicating that the depth of field is becoming shallower. Specifically, as shown in the chart, the depth of field goes from 0.18 to 0.08. The depth of field at this time is a value that does not pose a practical problem when photographing. Therefore, the boundary between the low magnification side and the high magnification side is the magnification value of the variable power lens when the depth of field is 0.08 in this case, that is, the magnification value of the lens 14b. However, at this time, since the switching switch S and the lighting variable resistor R _T are not switched, the illumination light amount of the photographing light source 5 and the illumination light source 4 remains constant, and as shown in FIG. illumination light ratio curve
It can be seen that the portion of L ₃ from lens 14a to lens 14b is horizontal, and the amount of illumination light from illumination light source 4 is constant. Specifically, as shown in the diagram, the illumination light ratio remains 1. In this case, the film exposure amount is adjusted to a constant value by changing the photographing aperture 12 from the aperture hole 12a to the aperture hole 12b in accordance with the change in magnification of the variable power lens 14 from the lens 14a to the lens 14b. Next, change the magnification variable lens 14 to the low magnification side lens 14b.
When the magnification is changed from to the lens 14c on the high magnification side, the diaphragm plate 30 rotates in conjunction with the rotation of the rotating disk 22.
12 from the aperture hole 12b of the photographing aperture 12.
c, but the opening degree is set to the same,
The depth of field remains constant. As shown in Figure 11,
Depth of field curve D ₃ from lens 14b to lens 1
The fact that the portion up to 4c is horizontal indicates that the depth of field is constant. Specifically, as shown in the chart, the depth of field remains unchanged at 0.08. At this time, selector switch S and lighting variable resistor
R _T is switched, and the amount of illumination light from the photographing light source 5 and the illumination light source 4 is increased. 12th
As shown in the figure, the lens 14b of the illumination light ratio curve _L3
The rise of the portion from the lens 14c to the lens 14c indicates that the amount of illumination light from the illumination light source 4 is increasing. Specifically, as shown in the chart, the illumination light ratio increases from 1 to 2.3, which is about half the illumination light ratio of 5.1 in the case of a conventional fundus camera, which increases only the amount of illumination light from the illumination light source. be. In this way, the amount of illumination light from the illumination light source 4 is controlled by the variable resistance R _T for illumination (light amount control means) shown in FIG.
As shown in Figure 2, it is controlled so that it changes only on the high magnification side. Also, the variable magnification lens 14 is set to the high magnification side lens 14c.
Even when the magnification is changed from 14d to 14d, the aperture of the photographic diaphragm 12 is the same as that of the lens 14b on the low magnification side, and only the amount of illumination light from the illumination light source 4 is increased. Since the same thing can be said, the explanation will be omitted. However, in terms of specific numbers, the illumination light ratio increases from 2.3 to 4.2. In this case as well, the illumination light ratio is approximately half of 9.4 in the case of a conventional fundus camera that increases only the amount of illumination light from the illumination light source, and moreover, the illumination light ratio when the lens 14c is used in the conventional fundus camera It is also 0.9 lower than the ratio of 5.1. In this way, the variable magnification lens 14 is changed from the lens 14b on the low magnification side to the lens 14c on the high magnification side, and from the high magnification side,
When changing the magnification from the lens 14c to the lens 14d, the amount of film exposure is increased by increasing the amount of illumination light from the illumination light source 4 to compensate for the lack of film exposure caused by keeping the aperture of the photographic diaphragm 12 constant. The adjustment is made constant, and the amount of increase in the amount of illumination light from the illumination light source 4 is not large compared to a conventional fundus camera. Therefore, even if the variable magnification lens 14 is changed from a low magnification side to a high magnification side, or from a high magnification side to an even higher magnification side, the depth of field remains the same as when the magnification is low, and only a part of the fundus is affected. There is no risk of the photograph being in focus, and the amount of increase in the amount of illumination light from the illumination light source 4 is small.
There is no fear that it will be too bright for the eye being examined. Although the explanation has been given using the illumination light source 4 as an example, it goes without saying that the same applies to the photographing light source 5. As described above, according to the present invention, the photographing aperture of the observation photographing system is varied in response to the change in the low magnification of the magnification of the variable magnification lens, and the fundus illumination is adjusted in response to the change in the high magnification. Since the amount of illumination light of the system is varied to keep the amount of film exposure constant, even if the photographing magnification is varied, appropriate exposure can be achieved and good photographing can be achieved. Moreover, when changing the magnification on the low magnification side, the amount of illumination light is kept constant and the shooting aperture is varied to keep the film exposure constant, but the depth of field changes due to the change in the shooting aperture at this time. Even if the aperture changes, the change in the photographing aperture is small, so the depth of field will not become so shallow that the photograph will be out of focus. In addition, at high magnifications, the photographic aperture is held constant and the amount of illumination light is varied to keep the film exposure constant, so even if the magnification is increased at high magnifications, the depth of field will decrease. It is possible to avoid inviting Moreover, since the illumination light intensity of the illumination light source is made to vary only at high magnification, even if it is applied to a fundus camera with large magnification changes and the illumination light intensity is increased as the magnification increases, the illumination light will remain unchanged. The burden on the eye to be examined can be kept within an acceptable range. As a result, it is possible to take in-focus photographs in the entire range from low magnification to high magnification, and it is possible to keep the burden on the eye to be examined due to illumination light within an allowable range. In addition, the boundary between the low magnification side and the high magnification side is the magnification value of the variable magnification lens when the depth of field is a value that does not pose a practical problem when the film exposure amount is constant and the photographic aperture is varied, When the magnification of the variable magnification lens is changed to the high magnification side, the photographing aperture is set to the same value as the low magnification side, and the light source is varied to keep the film exposure constant, so the depth of field becomes a value that is sufficient for practical use. Furthermore, the increase in the amount of illumination light can be suppressed to about half that of the conventional method, and the effect that the uneven fundus of the eye can be photographed in a good manner can be obtained without putting much burden on the subject's eye.

[Brief explanation of drawings]

Fig. 1 is a schematic explanatory diagram showing the optical system of a fundus camera that is an embodiment of the present invention, and Fig. 2 shows a rotating disc with a variable magnification lens and an aperture plate of the fundus camera attached to a rotating shaft. Front view showing the condition, Figure 3 is the 2nd
Figure 4 is a cross-sectional view taken along the - line in Figure 2, Figure 5 is an electric circuit diagram for changing the illumination light intensity of the photographing light source of the fundus camera, and Figure 6 is a cross-sectional view of the fundus camera. An electric circuit diagram for changing the amount of illumination light from the illumination light source. Figure 7 is a graph showing changes in the depth of field of a conventional fundus camera with variable photographic aperture. Figure 8 is a graph showing the illumination light ratio of the same fundus camera. 9 is a graph similar to FIG. 7 for a conventional fundus camera that changes the amount of illumination light, FIG. 10 is a graph similar to FIG. 9 for the same fundus camera, and FIG. 11 is an example of an implementation of the present invention. FIG. 12 is a graph similar to FIG. 7 for the fundus camera as an example, and FIG. 12 is a graph similar to FIG. 8 for the same fundus camera. 4...Light source for illumination, 5...Light source for photography, 12...
...Photographing aperture, 12a to 12d...Aperture hole, 14...
...variable magnification lens, 14a to 14d...lens.

Claims (1)

[Scope of Claims] 1. A fundus illumination system that has an illumination light source that illuminates the fundus of the eye to be examined, and an observation and photography system that has a variable magnification lens and a photography aperture that changes the magnification for observing and photographing the fundus of the eye to be examined. In the fundus camera capable of magnification, the photographing aperture is varied in response to a change in the lower magnification of the magnification of the variable magnification lens, and the photographing aperture is kept constant in response to a change in the higher magnification. , further comprising a light amount control means for varying the amount of illumination light from the illumination light source in response to changes on the high magnification side, thereby making the film exposure amount constant on the low magnification side and the high magnification side. A variable magnification camera. 2 The boundary between the low magnification side and the high magnification side is the magnification value of the variable magnification lens when the depth of field is a value that does not pose a practical problem when the film exposure amount is constant and the photographic aperture is varied. A variable magnification fundus camera according to claim 1.