JPH07313464A - Focusing detector of fundus oculi observation system - Google Patents

Abstract

PURPOSE:To exactly detect signals regardless of a difference in the reflectivity of the fundus oculi, variable power, etc., by providing this system with a subtraction means for determining a differential signal between the signal obtd. from a photoelectric converter at the time of projecting an index and the signal obtd. at the time of non-projecting and outputting a focusing signal and a driving means capable of varying the accumulation time of this photoelectric converter. CONSTITUTION:The light from a light source 16 forms an image after passing a slit. This light is again imaged near a holed mirror 9 by a relay lens 17b for projecting the index, a dichroic prism 7 and a relay lens 8 for a ring slit. The light is further imaged near the pupil of the eye 12 to be inspected by an objective lens 11, by which the fundus oculi is illuminated. The slit image from the fundus oculi is imaged near an array sensor 23 by a reimaging lens 21. The signal outputted from this array sensor 23 is inputted to a microcomputer, from which only the signal component is obtd. by obtaining the difference between the output of the array sensor 23 when the light source 16 for projecting the index is lighted and the output when the light source is turned off. The focusing information is thus obtd.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a focus detection device for a fundus camera.

[0002]

2. Description of the Related Art In a device for observing the fundus, it is difficult to focus due to insufficient light amount due to low reflectance of the fundus and poor contrast. Therefore, as seen in Japanese Examined Patent Publication No. 57-13294, there is proposed a device that projects an index on the fundus and focuses on the index image.

In this apparatus, the index image is divided by a split prism or the like to form an image on the fundus of the eye, and the lateral deviation thereof is observed and focused. Here, the observation optical system is only for observing the state of the lateral deviation, and the index projection optical system is used to directly focus on the fundus. Then, the index and the observation image plane (and the photographed image, if necessary) are made to cooperate by a mechanical interlocking device, and the index is conjugated with the fundus to indirectly focus on the fundus.

However, in such an indirect structure, the mechanical error of the interlocking device of the index projection optical system and the observation optical system or the error due to the difference between the optical systems (the index projection optical system has a large NA, and Since the peripheral light flux is used, the aberration becomes large, the observation optical system has a small NA, a large depth of focus, and the aberration is relatively small.), And the interlocking device itself becomes complicated. It had the drawback of increasing the size and cost. Also, when the magnification is changed, insufficient light may occur, and because the reflectance of the fundus varies depending on the site, the light receiving element (for example, CCD) may become saturated due to insufficient light at some sites or excessive light at other sites. However, there is a drawback that signal detection becomes difficult due to insufficient light amount.

Further, since there is a limit to the brightness of a light source that can enter the human eye, simply increasing the brightness of the light source to obtain a large signal necessary for focus detection may cause damage to the fundus. was there.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to solve these drawbacks and to provide a focus detection device capable of accurate signal detection regardless of the difference in reflectance of the fundus of the eye or zooming. With the goal.

[0007]

Therefore, the present invention has an index projection optical system for projecting a luminescent index on the fundus of the eye to be examined and a photoelectric converter for receiving the index of the fundus of the eye to be examined. By the output, in the focus detection device of the fundus oculi observation device having a focus information detection optical system for detecting the focus information,
Selection means for selecting whether or not to project the index, a first signal obtained from the photoelectric converter when projecting the index, and a second signal obtained from the photoelectric converter when the index is not projected And subtracting means for outputting a focus signal from the difference signal, and driving means capable of varying the accumulation time of the photoelectric converter in two steps.

[0008]

1 is a diagram showing the overall structure of a fundus camera having a focus detection device according to an embodiment of the present invention. Usually, the illumination system includes an observation illumination light source 1, a light source relay lens 2, a reflecting mirror 3, a strobe tube 4 and a ring slit 5, which are arranged conjugate with the light source 1 by the light source relay lens 2 (the plan view of FIG. ), A ring slit relay lens 6, 8, a perforated mirror 9, and an objective lens 11. The ring slit 5 is a relay lens 6, 8 for the ring slit,
As well known by the objective lens 11, the eye to be examined
The fundus camera and the eye to be examined 12 so that they are almost conjugated to the 12 corneas.
The working distance between and is adjusted. An index projection light source 16 that can be turned on and off by an index projection light source driving unit described below passes through an index projection relay lens 17a and illuminates a slit-formed index plate 18 (a plan view is shown in FIG. 4) from behind. To do.
The light source 16 forms an image after passing through the slit of the index plate 18, is imaged again near the perforated mirror 9 by the index projection relay lens 17b, the dichroic prism 7 and the ring slit relay lens 8, and further the objective lens 11 is formed. An image is formed in the vicinity of the pupil of the eye 12 to be inspected, and the fundus is illuminated. These light sources are depicted in dashed lines in FIG.

In the case of the optical system shown in FIG. 1, the index projection light source 16 is, for example, an infrared light emitting diode, and the dichroic prism 7 has characteristics of reflecting infrared light and transmitting visible light. Therefore, the dichroic prism 7 passes the visible light from the observation light source 1 and the strobe tube 4, but reflects the infrared light emitted from these light sources 1 and 4 to go out of the illumination optical system, and the fundus eventually becomes an index. It will be illuminated by infrared light from the projection light source 16. When the dichroic mirror 14 is made to have a characteristic of reflecting infrared light and transmitting visible light, the light reaching the array sensor 23 described later is only the transmitted light of the index plate 18 illuminated by the index projection light source 16, and the index image ( The slit image) has a relatively good contrast.

On the other hand, as shown by the dotted line in FIG.
The slit is imaged near the dichroic prism 7 by the index projection system relay lens 17b, and then imaged at the rear focal position of the objective lens 11 by the relay lens 8 and the perforated mirror 9. Therefore, the light transmitted through the slit that has passed through the objective lens 11 becomes substantially parallel light and enters the eye 12 to be inspected. If the eye 12 to be inspected is an emmetropic eye, the slit forms an image on the fundus. However, the slit image may be defocused depending on the diopter of the eye 12 to be inspected. But actually the index image 18
The light source illuminating is that the conjugate image is formed in the vicinity of the pupil with respect to the eye 12 to be examined, and the size of the light source image is small, so the numerical aperture (NA) of the light flux emitted from the slit is substantially reduced. , The depth of focus becomes deeper. Therefore, in the substantial range of the eye to be inspected (about ± 15 diopters), the blur of the image due to defocus is not so large, and the contrast that withstands the focus detection is guaranteed.

FIG. 2 shows only the focusing information detecting optical system in FIG. In the present embodiment, the focus information is obtained even for zooming and zooming, but for the sake of explanation, an operation at a certain magnification will be described, and then a device for zooming and zooming will be described. As shown by the solid line in FIG. 2, the slit image projected on the fundus serves as a secondary light source and serves as an objective lens.
After being imaged once by 11, the aperture of the perforated mirror 9,
After passing through the aperture stop 10 and the focusing relay lens 13, the light is reflected by a dichroic mirror 14 that transmits infrared light and visible light, and then an image is formed in the vicinity of the field stop 19. The field stop 19 is conjugated with the array sensor 23 by the re-imaging lens 21, and the array sensor 23 is conjugated with the imaging surface (observation image surface is not shown) 15. Therefore, the slit image from the fundus is imaged in the vicinity of the array sensor 23 by the re-imaging lens 21, but at that time, the pupil division roof type prism 22
(A three-dimensional view is shown in FIG. 5 ... In FIG. 1 and FIG. 2, the edges are drawn perpendicularly to the paper surface, which is for convenience of expression.
Actually, it is rotated by 90 ° around the optical axis and is arranged so that the ridge is parallel to the paper surface.) The light flux is divided into two parts, and each light flux is aligned with the direction of the ridge of the prism 22. Are arranged so that the cell array direction of the array sensor 23 is orthogonal to the paper surface).

Here, as shown by the dotted line in FIG. 2, the ridge of the prism of the pupil division prism 22 is formed by the focusing relay lens 13 and the field lens 20 behind the field diaphragm 19 and the aperture diaphragm 10.
Is almost conjugated with. Since the aperture stop 10 corresponds to the exit pupil of the focusing optical system, the image on the array sensor 23 is formed by the light fluxes from the two different parts of the pupil of the optical system. As is well known, the obtained two images are laterally offset from each other by the front pin and the rear pin. Therefore, the focus state can be detected by measuring the distance between the two images on the array sensor 23. That is, as shown by the solid line in FIG.
Assuming that the distance between the two images at the time of focusing is L, when the focal point is behind the field stop 19 (dotted line in FIG. 6), the image distance becomes narrower than L as shown by the dotted line in FIG. When the focal point is in front of the field stop 19, the image interval is wider than L.

Here, when the distance between the images is measured, the distance between the two image positions can be easily determined if the image itself is in a good image-forming state with good contrast. However, in practice, an image is often formed on the array sensor 23 in a defocused state, and a good image is not always obtained. Therefore,
Even under such bad conditions, the method proposed in Japanese Patent Laid-Open No. 54-68667 is used to accurately extract the lateral displacement of the image.

This is a method in which the image on the array sensor 23 is Fourier transformed, the phase component thereof is extracted, and the lateral shift is obtained by the transition theorem of Fourier transform. Array sensor
Assuming that the intensity of the image on 23 is the function f (x) of the position X, the Fourier transform F ₁ of the function f (x) before the displacement of the image is represented by the equation (1) where S is the spatial frequency. be able to.

[0015]

[Equation 1]

The Fourier transform F ₂ when this image is laterally displaced by α is given by equation (2) according to the transition theorem.

[0017]

[Equation 2]

Comparing equations (1) and (2), the magnitude of the Fourier component does not change due to the displacement, and only the phase is 2πas.
Since there is a shift, assuming that the shifted phase is Δθ, the displacement α can be obtained as in equation (3) by knowing Δθ.

[0019]

[Equation 3]

In order to realize this concretely, the spatial frequency is calculated by reciprocal of the sample length l on the array sensor 23 (1 /
As 1), discrete Fourier transform (DET) is performed. That is, as shown in FIG. 7, I _{1 is} an electric signal corresponding to the amount of light incident on each cell on the array sensor 23 for one of the two slit images on the array sensor 23, and the number of sampled cells is N ₁ sampled array sensor
With the length of 23 set to 1, the next electric quantities Ix and Iy are obtained.

[0021]

[Equation 4]

[0022]

[Equation 5]

These Ix and Iy are obtained by multiplying the real part (Ix) and the imaginary part (Iy) of the Fourier component of the spatial frequency 1 / l in the image on the array sensor 23 by N / 1. Therefore,
From Ix and Iy, the phase deviation angle θ of the Fourier component is obtained as shown in (6).

[0024]

[Equation 6]

When the image is laterally displaced, the phase deviation angle θ is displaced, and the amount of change in θ obtained by the calculation can be corrected to the lateral displacement according to the equation (3). Therefore, the following distance d is defined by the phase deviation angle θ as in Expression (7).

[0026]

[Equation 7]

This distance d is calculated for each of the two slit images on the array sensor 23, the distance between the two slit images is calculated, and the focus information is obtained by comparing this distance with the focus distance. be able to. As shown in FIG. 1, the array sensor 23 sequentially drives each cell by the signal from the driving unit 24, and sequentially outputs photoelectric conversion signals corresponding to each cell. From this output, computing means 25
Then, the motor M is driven by the motor driving means 26 based on the calculation result, and the focusing relay lens 13 is moved in the direction of the optical axis for focusing.

An electric processing system for performing the above processing is shown in the block diagram of FIG. 8, and its operation will be described with reference to FIG. 9 and the flowcharts of the microcomputer 252 shown in FIGS. In the block diagram of FIG. 8, the same members as those in FIG. 1 are denoted by the same reference numerals, but the array sensor 23 is called, for example, a charge coupled device (CCD), and a start signal from a well-known driving means 24 (see FIG. Each cell is driven by the clock pulse (FIG. 9C) following b)). That is, after the start signal is generated, an electric signal corresponding to the amount of light incident on the _first cell C ₁ of the array sensor 23 (FIG. 9A) by the first pulse P ₁ is an array sensor.
Output by 23. Also, for example, the seventh pulse P
_{At 7} , an electric signal corresponding to the amount of light incident on the _seventh cell C ₇ is output.

Output from the array sensor 23
Looking at the electrical signal, it contains various noise components.
It In other words, we want to obtain the light flux that enters the array sensor 23
Light flux from the slit image projected on the fundus as a signal component
S and observation N as an unnecessary noise component₁, Stray light N₂Light of etc
There is a bunch. Furthermore, due to the dark current of the array sensor 23 itself
Noise component N₃There is. Therefore, the array sensor 23
The electrical signal output from S + N₁+ N₂+ N ₃That
(Fig. 13 (a)). The above is the driving time for the light source for index projection
When the light source 16 for index projection is turned on by the path 253,
Next, consider the case where the light source 16 for index projection is turned off.
Then, the electric signal output from the array sensor 23 is unnecessary.
Observation light N as a significant noise component₁, Stray light N₂, Dark current N₃
Composite signal N₁+ N₂+ N₃(FIG. 13 (b)). So
Array sensor when the index projection light source 16 is turned on
The output of 23 (Fig. 13 (a)) and the light source 16 for index projection were turned off.
Difference from the output of the array sensor 23 (Fig. 13 (b))
By taking this, only the signal component S can be obtained (see FIG. 13).
(C)).

When the index projection light source 16 is turned on and off
The difference in the output of the array sensor 23 when
Explain. Photoelectrically converted by the array sensor 23
The electric signal is output at every storage time Tint of the array sensor 23.
I will be forced. Therefore, the light source 16 for index projection is turned off in advance.
Then, the period T (<Tint) during the first lighting is T₀As
(Step 100 in FIG. 10) At least one storage time Tin
Same as the Nth start pulse (Fig. 14 (a)) after t
In time (step 101 in FIG. 10), the index projection light source 16 is turned on.
Then (step 102 in FIG. 10), the array sensor output here is output.
The output of the sensor 23 is the value photoelectrically converted when the light source 16 is off.
It becomes the noise component of FIG. 13 (b). Output from array sensor 23
The input signal is sent to the A / D converter 251 via the amplifier 250 and so on.
Therefore, it is converted into a digital signal. This digital signal is
Input to the microcomputer 252. Ie my
Black computer 252 is synchronized with scanning of array sensor 23
The output I of the A / D converter 251_iRead in each cell
Corresponding memory M with built-in output_1-1, M_2-1To
Remember. (Step 103 in FIG. 10). Memory M here_1-1
Is almost left of the array sensor 23 as shown in FIG.
Half length l₁Memorize the signal from the cell group of
Re M_2-1Is also in the right half of array sensor 23
Length l₂The signal from the cell group will be stored. Ma
Microcomputer 252 has been in the predetermined period since the light source 16 was turned on.
It is detected that the time T has passed (step 104 in FIG. 10), and
Turn off the source 16 (step 105 in FIG. 10). Next N + 1
Array sensor 23 output synchronized to the start pulse of
Is a value obtained by photoelectric conversion when the light source 16 is turned off.
Signal component + noise component (step 106 in FIG. 10). This
The output signal of is similar to the processing when only the noise component
And memory M_1-2, M_2-2Stored in the
107). Light source 16 for index projection in step 105 of FIG.
The timing of turning off the light will be described later.
The computer 252 is a memory M_1-1, M_1-2, M_{2- 1},
M_2-2It is determined whether or not the stored value of, is greater than or equal to a predetermined value.
(Step 108 in FIG. 10), if the value is less than or equal to the predetermined value, the stored value
Out of memory M_1-2To memory M_1-1The difference between the memory
M₁Stored in the memory M_2-2To memory M_2-1Difference from
Tori memory M ₂(Step 109 in FIG. 10). That
Memory M₁, M₂From the magnitude of the value stored in
The period T for turning on the light source 16 is determined (step in FIG. 10).
110).

Next, the microcomputer 252 has a memory M.
_The equation (4), the equation (5), the equation (6), and the equation (7) are sequentially calculated according to the stored value of ₁ , and the obtained distance d ₁ is stored in the memory M.
_It is stored in ₃ (step 111 in FIG. 11). Similarly, the distance d ₂ obtained from the stored value of the memory M ₂ is stored in the memory M ₄ (step 112 in FIG. 11). Next, the microcomputer 252 determines the stored values d ₁ and d ₂ of the memories M ₃ and M ₄ and the distance l.
_The calculation (l ₁ −d ₁ + d ₂ ) is performed with respect to ₁ (step 113 in FIG. 11). Then, the value obtained in step 113 (ld
₁ + d ₂ ) ... This value corresponds to the distance between two slit images, and is compared with the distance at the time of focusing to find the difference, and this difference may be used as focusing information.

The motor driving means 26 inputs a pulse signal having a different frequency to the motor M according to the focus information output from the microcomputer 252. At that time, motor M
The frequency of the signal input to is large when the focusing relay lens 13 largely deviates from the in-focus position. Therefore, the motor M rapidly rotates, and the pulse signal becomes small when the focusing relay lens 13 approaches the in-focus position. The motor M is controlled to rotate at a low speed so that the motor M immediately stops at the in-focus position.

Step 10 of the above flow chart will be described below.
8, 110 and focusing control according to zooming will be described in detail.
Step 108 turns on the array sensor 23 by blinking.
When the amount of light becomes large, the focus cannot be controlled and the measurement is performed again.
Judgment is made to restore the constant value, and the incident light quantity
If it is less than a predetermined value, focus control is possible. By the way
The reflectance of the fundus differs considerably depending on the site. For example milk
The reflectance of the head is about 10 times larger than that of the macula.
Yes. Therefore, the output of the light source 16 was obtained by the focus detection system.
Memory M₁, M₂The maximum value of the memorized value of the
If you do not control it like this, the light intensity will be insufficient in the macular region.
The array sensor 23 gets tired due to excessive light on the nipple or the nipple.
There is a possibility of harmony. Therefore, in the focus detection system described above
In order to maintain a constant level, the array sensor
-23 can be controlled to some extent by controlling the accumulation time
However, controlling the storage time will affect the dark current.
Sound to reduce the dynamic range of the array sensor 23.
Will be lost. Therefore, in step 110,
The light source 16 turns on within the accumulation time.
Control T via the index projection light source drive circuit 253
By doing so, a signal of a constant level is obtained. Already mentioned
As shown in Fig. 14 (a), the start pulse and Fig. 14 (b) are
In the relationship between the turn-off period and the turn-on period of the light source 16, for example, the period T₁
Is the focus detection system and turns on the light source 16 when the signal level is high.
Showing the time. Also period T ₂If the level is small
The lighting time of the light source 16 is shown. But actually this
Brightness of the light source that can enter the human eye when trying to realize
Since there is a limit to the
Programmer capable of gaining the amplifier 250 etc. for amplifying the signal
The gain of the bull amplifier and the amplifier
By controlling with 2
Is it a very small signal combined with the control of the lighting time?
Even if you realize a large signal from a small portion
Good.

Next, zooming and zooming will be described. Scaling,
The following ideas were made in the optical design so that the focus can be detected even when zooming. When the magnification is changed and the zoom is performed, the focus position on the array sensor 23 and the size of the index image can be known. FIG. 12 shows the movement of the image on the array sensor 23 when the magnification is changed. (Inspection eye OD) Considering the size of the array sensor 23 sufficiently, the movement due to the diopter of the eye (horizontal displacement of the image on the array sensor 23) at the time of high magnification is larger than that at the time of bottom magnification, so that it is practical The magnification of the focus detection optical system (field lens 20) so that the eye diopter (about ± 15D) is satisfied.
And the size of the index (slit) is determined. It should be noted here that the two slit images divided into the pupils should not be bulky.

The operation of focus detection with variable magnification and smoothness thus configured is as follows. For example, let us take an example of a case where the variable magnification is 3 times. In that case, the focusing relay lens 13 in FIGS. 1 and 2 may be replaced with another focusing relay lens 13a by a turret or the like.

Focusing intervals A, B, and C corresponding to a-times (low-magnification), b-times (medium-times), and c-times (high-times) are stored in a microcomputer, and information of magnification change is obtained from a fundus observation device. (Steps 114 and 115 in Fig. 11)
The calculation result obtained in 113 is compared with the focusing interval at each magnification (steps 116, 117 and 118 in FIG. 11) to obtain the focusing information (step 119 in FIG. 11). Similarly, when zooming, the array sensor 23
The variation of the in-focus position at each magnification above is put on a curve, stored in a microcomputer, and the zoom information is received from the fundus observation device to obtain the position at that magnification. The same processing as that described in steps 114 to 119 may be performed.

Here, the method of removing the various noise components N ₁ , N ₂ and N ₃ has been described above. However, in the previous method, at least 2 accumulation times were required to perform one processing. How to do is described. FIG. 14 (a) shows an array sensor driving means capable of varying the accumulation time in two steps, that is, the accumulation time when the light source 16 is turned on is Tinton.
The same accumulation time, that is, T ₂ is set. Also, assuming that the storage time when the light is off is Tintoff, Tintoff <Tinton
It will be set so that

In this way, even if only the signal component is obtained by the above-mentioned method, the accurate signal component cannot be obtained because the length of the accumulation time differs depending on whether the light is on or off. That is,
This is because the photoelectric output of the array sensor 23 is proportional to not only the amount of incident light but also the storage time. Therefore, the dark output value of the array sensor 23 is stored in advance as Tinton and Tinto.
It is measured by ff and is stored in the memory as Ninton and Nintoff (output of array sensor 23 = photoelectric conversion component by incident light amount + dark output component).

Further, the proportional constant K of photoelectric conversion between the accumulation times Tinton and Tintoff for the same incident amount of the array sensor 23.
Is measured and stored in memory. In this way, the array sensor data Sint read when reading the signal component accumulated in the array sensor when the light is turned off
Calculate (Sintoff-Nintoff) * K for off. (Sinton−Ninton) − (Sintoff−Nintof) is calculated for the data at the time of lighting with respect to Sinton.
Only the signal component can be obtained by obtaining f) × K.

If the dark output value can be ignored for the signal component, it is sufficient to obtain (Sinton-Sintoff) × K. In that case, the reference power source Vref of the A / D converter is set to Tinton and Tin in synchronization with the array sensor driving means.
Ratio of proportional constant K of photoelectric conversion with toff, that is, Vrefon
Switch to Vrefoff (Vrefon = Vrefoff × K),
If two A / D converters using Vrefon and Vrefoff as reference power supplies are used to switch the A / D converters, the proportional constant K is multiplied after reading the array sensor output accumulated when the light source 16 is turned off. It is not necessary, and the output value becomes smaller by further shortening the accumulation time, and it is possible to avoid a decrease in the dynamic range due to that.

In the above description, the index plate 18 is illuminated from behind by the index projection light source 16 and the slit of the index plate 18 is used as a light emitting index. However, a rectangular light emitter is provided instead of the slit. Needless to say, the light emitting body may be used as the light emitting index. In addition, in order to change the light amount of the index, various other light amount adjusting means such as a diaphragm and ND
The use of filters can be considered as well.

[0042]

As described above, by carrying out the present invention, optical noise (noise due to observation light, stray light, etc.) and electrical noise can be eliminated, and by controlling the light amount of the index, it can be anywhere on the fundus. Accurate focus detection is now possible.

[Brief description of drawings]

FIG. 1 is a diagram showing an optical system and an electric block of a fundus camera having an embodiment of the present invention.

FIG. 2 is a diagram showing only a focus detection optical system and an observation optical system in FIG.

FIG. 3 is an enlarged plan view of a ring slit.

FIG. 4 is an enlarged plan view of an index having an index.

FIG. 5 is an enlarged perspective view of a pupil division roof prism.

FIG. 6 is an enlarged view of the main part of the focusing information detection optical system.

FIG. 7 is a diagram showing an intensity distribution of a light image on an array sensor.

FIG. 8 is a detailed view of the electric block of FIG.

FIG. 9 is a diagram showing a drive state of an array sensor.

10 is a flowchart for explaining the operation of the microcomputer used in FIG.

11 is a flowchart for explaining the operation of the microcomputer used in FIG. 8 continued from FIG.

FIG. 12 is a diagram showing movement of a slit image (inspection eye OD) during focusing when zooming.

13 (a), (b), (c)] Diagrams showing signal component + unwanted noise component (a), undesired noise component (b), and signal component (c), respectively.

14 (a), (b): Start pulse (a), light source 16
Showing the relationship (b) between the extinguishing period and the lighting period of

15 (a), (b): Light source 16 for start pulse (a)
Showing the relationship (b) between the extinguishing period and the lighting period of

[Explanation of symbols for main parts]

 7 Dichroic prism 8 Relay lens for ring slit 9 Perforated mirror 10 Aperture stop 11 Objective lens 13 Relay lens 13a Variable magnification relay lens 14 Dichroic mirror 16 Light source for index projection 17a, 17b Index projection system relay lens 18 Index plate 19 Field stop 20 field lens 21 re-imaging lens 22 pupil-split roof prism 23 array sensor 24 driving means 25 computing means 26 motor driving means M motor 252 microcomputer 253 light source driving circuit for index projection

Claims (1)

[Claims] 1. An index projection optical system for projecting a luminescent index onto the fundus of the eye to be examined and a photoelectric converter for receiving the index of the fundus of the eye to be examined, and a focus information is detected by the output of the photoelectric converter. In a focus detection device of a fundus oculi observation device including a focus information detection optical system, selection means for selecting whether or not to project the index, and a first signal obtained from the photoelectric converter when projecting the index. And a subtraction means for obtaining a difference signal between the second signal obtained from the photoelectric converter when the index is not projected, and outputting a focusing signal from the difference signal, and a storage time of the photoelectric converter in two stages. A focus detection device comprising: a variable drive unit.