JPH0786588B2 - Focus detection device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a focus detection device attached to an optical device such as a microscope or a projector to detect a focus state.

[Prior Art] Conventionally, as a device for detecting a focus state, there is a focus detection device Db shown in FIGS. In other words, the focus detection device Db has a configuration in which the point on the observed object side focus 23b of the objective lens 2b is focused on the ridge 15b of the prism 6b.
Therefore, in the focus detection device Db at the time of focusing, the light from the light emitting element 1b is reflected by the half mirror 3b after passing through the observed object 13b, and is split by the ridge 15b of the prism 6b.

It should be noted that FIGS. 10, 11 and 12 show that the relative position between the focus detection device Db and the observed object 13b is close, in focus and far away, respectively.

[Problems to be Solved by the Invention] In the focus detection device Db, detection is sensitive when a focused state is not obtained, that is, so-called defocus.

However, the ridge 15b of the prism 6b is extremely difficult to manufacture in a predetermined manner, and when the ridge 15b has a minute roundness or an error in the shape, the light from the half mirror 3b is not split as predetermined, and therefore, as predetermined. If the light is not divided, there is a problem in that the light as designed does not enter the light receiving elements 7b, 8b, 9b, 10b side and the predetermined focus detection operation is not performed.

As a means for solving this problem, there is a focus detection device Dc shown in FIGS. That is, in the focus detection device Dc, the light reflected by the half mirror 3c from the observed object 13c is split by the prism 6c and reaches the light receiving elements 7c, 8c, 9c, 10c side. However, in the focus detection device Dc, the light receiving elements 8c and 9c receive light as shown in FIG. 13 when the observed object 13c is closer to the focal point 23c. On the other hand, if the object to be observed 13c is located far from the focal point 23c,
As shown in the figure, the light receiving elements 7c and 10c receive light. However, when the object to be observed 13c is further distant from the focal point 23c, the light receiving elements 8c and 9c receive light as shown in FIG. 16, and the object to be observed 13c is closer to the focal point 23c. Produces the same result as. Therefore, the focus detection device Dc can determine whether it is in the in-focus state or the out-of-focus state, but the observed object 13c is located closer to the focus 23c in the out-of-focus state. It is not possible to determine whether or not it is in a distant position. Therefore, in order to obtain the focus state, the focus detection device
There is a problem that it may be necessary to perform two trial and errors of approaching and separating Dc from the observed object 13c.

The present invention has been made in view of the above circumstances, and it is not necessary for the ridge of the prism to be manufactured with high accuracy, and it is possible to detect the focused state even if the ridge has a slight roundness or some error in the shape. (EN) Provided is a focus detection device which has no problem and is capable of discriminating whether an object to be observed is near or far from the focus when it is out of focus.

[Means for Solving the Problems] According to the present invention, a light emitting element and an objective lens, which are arranged with a first optical axis in common, are provided between the light emitting element and the objective lens, and the reflection surface is the above-mentioned. A half mirror arranged so as to intersect with one optical axis at a constant angle, and a second mirror extending from the intersection of the reflecting surface side of the first optical axis of the half mirror with respect to the half mirror at the constant angle. Between the light receiving element disposed on the optical axis side of the, and the light receiving element and the half mirror,
A prism whose ridge is arranged on the second optical axis and between the prism and the half mirror, and the optical axis is common to the second optical axis, and the object to be observed of the objective lens An imaging lens for forming an image of a point on the second optical axis, the side focus of which is imaged by an objective lens, on the light receiving element, comprising: The focus detection device is characterized in that the ridge of the prism is located at the image-side focal point of the objective lens formed by.

[Function] The object-side focal point of the objective lens is imaged by the objective lens between the objective lens and the imaging lens, and the light from the combined image to the light receiving element is in a state of a light flux with a cross section expanded. Then enter the prism.

The image-side focal point of the objective lens is imaged by the imaging lens at the ridge position of the prism, and the light coming through the half mirror of the object to be observed is reflected by the half mirror regardless of the amount of deviation from focusing. An image is formed at a distance from the prism and the prism divides the image into two.

Embodiments The present invention will be described in detail based on the embodiments shown in FIGS. However, this does not limit the present invention.

As shown in FIG. 1, the focus detection device D includes a light emitting element 1,
Objective lens 2, half mirrors 3 and 4, and imaging lens 5
, Prism 6, light receiving elements 7, 8, 9, 10 and differential amplifier 11
Is provided.

The light emitting element 1 and the objective lens 2 have their respective optical axes.
Are arranged in common. Therefore, the light from the light emitting element 1 passes through the half mirrors 3 and 4 and the objective lens 2 to the side of the observed object 13.

The half mirror 3 is arranged so as to intersect the optical axis 12 at 45 degrees. Therefore, the light reflected by the half mirror 4 from the observation object 13 side through the objective lens 2 is reflected by the half mirror 3 and proceeds to the imaging lens 5 side. At this time, the light reflected by the half mirror 3 has an optical axis 14 extending at an angle of 45 degrees with respect to the half mirror 3.

The imaging lens 5 is arranged with the optical axis 14 as the optical axis.

The prism 6 is arranged such that the ridge 15 is located on the optical axis 14. Further, in the prism 6, the ridge 15 is located at the position 17 where the image-side focus 16 of the objective lens 2 is imaged by the imaging lens 5.

2 to 4, the operation when the focus detection device D is incorporated in a microscope (not shown) will be described. The microscope includes a table 18 on which an object 13 to be observed is placed, a rack 19 and a pinion gear 20 for moving the table 18 toward and away from the objective lens 2, a camera 21 for detecting the object 13 to be observed as an image, and a monitor. Is configured with a CRT22 for. As shown in FIG. 2, the focus detection device D detects from the light emitting element 1 when the observed object 13 is closer to the objective lens 2 than the focal point 23 of the objective lens 2 on the observed object 13 side. Light passes through the half mirror 3, is reflected by the half mirror 4, and further passes through the objective lens 2.
Leading to. The light reaching the object 13 to be observed is reflected, returns, passes through the objective lens 2 again, is reflected by the half mirrors 4 and 3, and forms an image at the image forming point 24. At this time, the image forming point 24 is located relatively close to the image forming lens 5. The light imaged at the image forming point 24 travels along the optical axis 14 through the image forming lens 5 and enters the prism 6 to be split.

Here, when this light enters the prism 6, the image forming point 24 is located between the image side focus 16 of the objective lens 2 and the prism 6, and the image forming lens 5 forms the image forming point 24 at the light receiving element 7. Since the image is formed on the 8, 8, 9, 10 side, the light enters in the state of a light flux whose cross section is not a point but a spread. Therefore, even if the shape of the ridge 15 of the prism 6 has a slight roundness or an error with respect to a predetermined shape, the light is split as predetermined and reaches the light receiving elements 7, 8, 9, 10 side as designed. Therefore, the prism 6 does not need to manufacture the ridge 15 with extremely high accuracy.

The light that has entered the prism 6 is split into two, refracted inward with respect to each other, and further refracted inward with each other, and then exits from the prism 6. The two split lights emitted from the prism 6 reach the light receiving elements 8 and 9 after they have finished intersecting with each other.

The light receiving elements 8 and 9 receive the light from the prism 6 and output a large current. On the other hand, since the light receiving elements 7 and 10 do not receive light, the current output is small. Differential amplifier 11
Input the signal by the current from the light receiving element 7,8,9,10,
A signal for discriminating focusing is output, which is the difference between the outputs from the light receiving elements 8 and 9 and the outputs from the light receiving elements 7 and 10. Now, the relationship between the output of the differential amplifier 11 and the distance from the in-focus position of the observed object 13 is as shown in the graph of FIG. Therefore, the difference between the outputs of the light receiving elements 8 and 9 and the outputs of the light receiving elements 7 and 10 is located at the point 25, which means that the observer has a negative value with respect to the objective lens 2 from the in-focus position of the observed object 13. Know that the position is too close to the focus position. The observer preferably separates the relative position between the object 13 to be observed and the focus detection device D in order to obtain the focused state.

At this time, the light starting from the object 13 to be observed and passing through the objective lens 2 and the half mirror 4 forms an image behind the camera 21, and an unclear image appears on the CRT 22.

Now, rotate the pinion gear 20 in the direction of arrow A to rotate the table.
When the relative position between the object 14 to be observed and the focus detection device D is separated by sliding 18 downward, the object 13 to be observed and the focal point 23 of the objective lens 2 coincide with each other. At this time, how the light from the light emitting element 1 travels is as shown by the arrow in FIG.
First of all, the light emitting element 1 starts, passes through the half mirror 3, is reflected by the half mirror 4, and further passes through the objective lens 2 to reach the observed object 13. The light reaching the object 13 to be observed is reflected and returned, passes through the objective lens 2 again, and then is reflected by the half mirrors 4 and 3 to form an image at the image forming point 24. The imaged light passes through the imaging lens 5, enters the prism 6 in the state of a light flux in the cross section, is split into two, and exits from the prism 6, and the two split lights are received after they intersect with each other. Element 7,
To the junction of 8 and 9,10. The light receiving elements 7, 8, 9 and 10 receive weak light having substantially the same intensity and output a small current. The differential amplifier 11 receives current signals from the light receiving elements 7, 8, 9 and 10 and outputs a difference between outputs from the light receiving elements 8 and 9 and outputs from the light receiving elements 7 and 10. The output of this difference is located at point 26 in FIG. 5, and the observer knows that the observed object 13 is in the in-focus position. At this time, the light originating from the object to be observed 13 and passing through the objective lens 2 and the half mirror 4 is imaged by the camera 21. The CRT21 receives a signal from the camera 21 and projects a clear image.

From the in-focus state obtained above, the pinion gear 20 is rotated in the direction of arrow A to separate the relative position between the object to be observed 14 and the focus detection device D. At this time, the light from the light emitting element 1 travels as shown by the arrow in FIG. That is, the light from the light emitting element 1 sequentially enters the prism 6 through the half mirrors 3 and 4, the objective lens 2, the observed object 13, the objective lens 2, the half mirrors 4 and 3, and the imaging lens 5. The light entering the prism 6 has a cross section similar to that when the object 13 to be observed is closer to the objective lens 2 than the focal point 23 of the objective lens 2 and when the object 13 to be observed is in the in-focus position. Enters in the state of a spread light flux. The light entering the prism 6 is split into two and intersects before reaching the side of the light receiving elements 7, 8, 9 and 10. The two lights that have been divided and intersected reach the light receiving elements 7 and 10, respectively. The light receiving elements 7 and 10 receive the light from the prism 6 and output a large current. On the other hand, the light receiving elements 8 and 9
Has a small current output because it receives no light. The differential amplifier 11 inputs the signals due to the currents from the light receiving elements 7, 8, 9 and 10, and outputs the signals from the side of the light receiving elements 8 and 9 and the light receiving element 7.
And the difference from the output from the 10 side is output. The output of this difference is located at a point 27 in FIG. 5, and it can be seen that the observer is in a state in which the relative position between the object to be observed 13 and the objective lens 2 is farther from the focused state. Further, at this time, the light that has started from the object to be observed 13 and has passed through the objective lens 2 and the half mirror 4 forms an image in front of the camera 21, and an unclear image appears on the CRT 22.

Here, further rotate the pinion gear 20 in the direction of arrow A,
The relative position between the object to be observed 13 and the focus detection device D is further separated. At this time, the light from the light emitting element 1 travels as shown by the arrow in FIG. That is, the light from the light emitting element 1 is
Sequential half mirrors 3 and 4, objective lens 2, object to be observed 1
3, the objective lens 2, the half mirrors 4 and 3, and the image forming lens 5 enter the prism 6. The light entering the prism 6 is in the state of a light flux whose cross section is widened as in the case where the relative position between the object to be observed 14 and the focus detection device D is separated from the focused state described above. Moreover, similarly, light is split into two by the prism 6, refracted inwardly from each other, exits from the prism 6, crosses each other, and reaches the light receiving elements 7 and 10. The two divided lights are refracted inwardly by the prism 6 and intersect with each other.
It is located closer to the light receiving elements 7, 8, 9 and 10. Therefore, the two split lights both try to form an image at a position distant from the prism 6 with respect to the image forming lens 5, and do not form an image at a position closer to the prism as shown in FIG. Moreover, since the relative position between the object to be observed 13 and the focus detection device D is sufficiently separated as compared with the in-focus state, the distance between the image forming point 24 and the image forming lens 5 is large, The incident angle of the light coming from the imaging lens 5 and entering the prism 6 is larger, and as a result, the lights that are split by the prism 6 and travel toward the light receiving elements 7, 8, 9, 10 intersect with each other to the outside. Go to Therefore, the two split lights reach the light receiving elements 7 and 10 as in the case shown in FIG. 4, and the light receiving elements 8 and 9 as shown in FIG.
Never reaches. Therefore, in the focus detection device D, when the relative position with respect to the observed object 13 is near, in focus, and far, respectively, the light receiving elements 7, 8, 9, 10 receive only one light. Therefore, in the non-focused state, it does not occur that the relative positions are close or distant. That is, in the non-focused state, the observer can know whether the relative position between the object 13 to be observed and the focus detection device D is closer or farther than in the focused state, and therefore, the closeness or the farness. Based on how the relative positions are separated or approached, the focused state can be easily obtained.

6 to 9 show another embodiment of the present invention. As shown in FIG. 6, the focus detection device Da is provided with a collimator lens 28a and a half mirror 29a for converting the light from the light emitting element 1a into parallel light between the half mirrors 3a and 4a. Therefore,
In the focus detection device Da, the light emitted from the light emitting element 1a passes through the half mirror 3a, then becomes parallel light by the collimator lens 28a, is reflected by the half mirrors 29a and 4a, and enters the objective lens 2a. Further, the light reaches the observed object 13a and returns,
An image is formed at a point 24a on the optical axis 14a through the objective lens 2a, the half mirrors 4a and 29a, the collimator lens 28a, and the half mirror 3a. The imaged light passes through the imaging lens 5a, is incident on the prism 6a in the state of a light beam having an expanded cross section, and is split into two. The two divided light beams are refracted inward, go out from the prism 6a, are refracted further inward, and intersect each other before reaching the light receiving elements 7a, 8a, 9a, 10a side. Light receiving element 7a, 8a, 9a, 10a
Receives the light and outputs a current to the differential amplifier 11a. The differential amplifier 11a receives an electric current and receives an object to be observed 13a and a focus detection device.
A signal indicating that the relative position to Da is in focus, closer to, or farther from the focus is output as a signal.

Figures 7, 8 and 9 show the optical path system when the focus detection device Da is installed in a microscope (not shown).
It indicates that the relative position between a and the focus detection device Da is closer to the in-focus state, is in the in-focus state, and is farther than the in-focus state.

The microscope incorporating the focus detection device Da is a half mirror 4a.
A filter 30a for adjusting the amount of light and a light balance and an imaging lens 31a for the camera 21a are provided between the camera and the camera 21a. 32a is a halogen lamp for illumination.
Illumination lenses 33a and 34a are provided between the halogen lamp 32a and the half mirror 3a.

In both of the two focus detection devices D and Da described above, the ridges 15 and 15a of the prisms 6 and 6a are located on the imaging lens 5 and 5a side, respectively. However, the structure may be such that the ridge of the prism is located on the light receiving element side.

When the focus detection device is incorporated in a microscope, a drive motor and control means may be provided between the pinion gear for moving the table up and down and the differential amplifier so that automatic focus can be obtained. .

In addition to the microscope described above, a projector or the like may be incorporated in the focus detection device.

[Effect of the Invention] According to the present invention, even if the ridge of the prism has a minute roundness or an error in the shape, the light can be split in a predetermined manner, and high precision is not required for manufacturing, so that the cost can be reduced. In addition, it is possible to determine whether the relative position with respect to the observed object is closer or farther than the in-focus state when it is in the out-of-focus state, so that the in-focus state can be easily obtained based on the determination result. The effect is obtained.

[Brief description of drawings]

FIG. 1 is a structural explanatory view showing an optical path system of an embodiment of the present invention, and FIGS. 2, 3 and 4 show the relative positions of the object to be observed are too close when the embodiment is incorporated into a microscope. FIG. 5 is a diagram showing the relationship between the output of the differential amplifier of this embodiment and the distance between the object to be observed and the objective lens, and FIG. 6 is a diagram of the present invention. FIG. 1 is a view corresponding to FIG. 1 of another embodiment, and FIGS. 7, 8 and 9 are views corresponding to FIG. 2 of another embodiment, respectively.
Fig. 3 equivalent diagram, Fig. 4 equivalent diagram, Fig. 10, 11, 12 are equivalent to Fig. 2 of the conventional example, Fig. 3 equivalent diagram, Fig. 4 equivalent diagram, respectively.
FIGS. 13, 14, and 15 are other conventional examples corresponding to FIG. 2, FIG. 3, equivalent diagram, FIG. 4 equivalent diagram, and FIG. 16 are other conventional examples corresponding to other corresponding FIG. FIG. 17 is a view corresponding to FIG. 1 in which the relative position to the object to be observed is too far away when this embodiment is incorporated in a microscope. D: Focus detection device 1 ... Light emitting element, 2 ... Objective lens, 3,4 ... Half mirror, 5 ... Imaging lens, 6 ... Prism, 7,8,9,10 ... Element, 12,14 ... Optical axis, 15 ... Prism edge, 16,23 ... Focus, 17 ... Imaging point.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location G03B 3/00 A

Claims (1)

[Claims] 1. A light-emitting element and an objective lens, which are arranged so as to share a first optical axis, and a reflection surface between the light-emitting element and the objective lens and at a constant angle with the first optical axis. And the second optical axis formed by extending at a certain angle with respect to the half mirror from the intersection of the reflecting surface side of the half mirror and the first optical axis of the half mirror. A light receiving element, a prism whose ridge is arranged on the second optical axis between the light receiving element and the half mirror, and between the prism and the half mirror and whose optical axis is the second light An imaging lens, which is disposed in common with the axis and forms an image on the second light receiving element on the second optical axis at which the observation-side focal point of the objective lens forms an image by the objective lens. In the focus detection device provided with, the objective lens for forming an image by the image forming lens A focus detection device, characterized in that the ridge of the prism is located at the image-side focal point.