JPS6260645B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an active distance measuring device, and is particularly suitable for a distance measuring device for automatic focus adjustment.

Rangefinders, and especially rangefinders for achieving automatic or semi-automatic focus adjustment, can be broadly divided into passive and active types, and while many proposals have been made to date, there are already intermediate-level rangefinders that perform automatic focus adjustment. Still cameras or small cine cameras are used by amateur camera enthusiasts. Most of the automatic focusing cameras currently in use today use light-receiving type distance measuring devices. However, the active type is attractive because it has the inherent ability to improve ranging accuracy.

Active devices that project a beam of light onto an object to be measured and capture the reflected light to measure distance are basically based on the principle of triangulation, using a procedure equivalent to measuring the angle that extends the baseline length. It will be done. In conventional methods, two light receiving elements are provided to detect the light beam scattered and reflected by the object to be measured, these elements receive the light beam, and the difference between the output signals is used. It is common to determine whether the focal point is in front or behind the object. However, with this method, the differential output is not stable due to signal drift and noise generated in the light receiving element and its amplification system, resulting in a decrease in accuracy.

The present invention aims to eliminate this type of drawback, provide a configuration that allows detection with the same light receiving element, and improve distance measurement accuracy.

A basic embodiment will be described below with reference to FIGS. 1 to 6.

In FIG. 1, the symbol L is the base line length. Also with A ₁
A ₂ is a light source that can be amplitude modulated, such as a light emitting diode, and blinks rapidly, but if it is a light source with poor response, such as a tungsten lamp, it may be blinked by a shutter. Reference numeral B designates a projection mask, which is provided with two slits _B1 and _B2 separated by an interval S as shown in the plan view in FIG. 2, and these slits function as distance measurement marks. Further, the projection mask B is arranged so that the optical axis of the projection lens C passes through the midpoint between the slits _B1 and _B2 , and the slits _B1 and _B2 are aligned in the base line length direction. Also each slit
Light sources A ₁ and A ₂ are arranged to correspond to B ₁ and B ₂ .

D is an object to be measured, and F is a scanning mirror, which is arranged in front of the light-receiving lens G so as to be rotatable about an axis perpendicular to the optical axis of the light-receiving imaging lens G. H is a detection mask which includes two slits H ₁ and H ₂ separated by a distance t as shown in a plan view in FIG.
Although the interval t is slightly larger than the interval S in Fig. 2, it may be slightly smaller, and the deviation amount is 2.
It should not be so large that two mask images fit between two detection slits, nor should it be so small that two detection slits fit between two mask images. The slits H ₁ and H ₂ function as detection areas, and are arranged in the base line length direction so that the slit intervals are equally distributed along the optical axis of the light receiving lens G.

is a photoelectric conversion element, which is placed close to the detection mask.

In the above configuration, the light source A ₁ is blinked according to the chart in FIG. 6 1, and the light source A ₂ is blinked according to the chart in FIG.
If it flashes according to the chart, i.e. the light source
When A ₁ and A ₂ are turned on alternately, the slits B ₁ and B ₂ of the projection mask B are sequentially illuminated by the corresponding light sources A ₁ and A ₂ , respectively, so that the light beam emitted from the slit B ₁ or B ₂ is transmitted to the projection lens. G and forms a slit image, that is, a mark image, on the object D. The light beam reflected by the object D is scanned by a scanning mirror F, and an image is formed on a detection mask H by a light receiving lens G. Figures 4 and 5 show images B ₁ ' and slits B ₁ and B ₂ .
Although the detection mask H formed with B ₂ ′ is depicted,
In the case of Fig. 4, the setting angle of the scanning mirror is optimal, and the projection slit images B ₁ ' and B ₂ ' are equally distributed over the detection slits H ₁ and H ₂ , so that the light source A Even when ₁ and _A2 blink, the amount of light incident on the photoelectric conversion element does not change. FIG. 71 depicts the output signal from the element at that time, and although the signal level is lower than in the case described later, it appears as a direct current.

On the other hand, when the angle of the scanning mirror is inappropriate, for example, as shown in Fig. 5, the image B ₁ ' of the slit in the projection direction almost matches the detection slit H ₁ ,
_B2 outputs an alternating current as shown in 2 in FIG. 7 when the detection slit _H2 is only slightly crossed. If the scanning mirror F is oscillated in the opposite direction from the optimum position, it outputs an alternating current with an opposite phase as shown in 3 in FIG. Therefore, by comparing the phase relationship between the blinking of the light source and the output AC signal, the direction in which the scanning mirror should be rotated can be determined. Therefore,
Distance measurement is achieved by rotating the scanning mirror in a determined direction until the signal from the element becomes a direct current, that is, until the output becomes constant, and the distance corresponds to the amount of rotation of the mirror.

Next, an embodiment will be described in which the distance measuring device described above is applied to a fundus camera, but this device is also suitable for a single-lens reflex camera or a cine camera that measures distance through a focusing lens. In addition, in the configuration shown in Figure 1, the two lenses C and G are fixed, and the two slit images formed on the detection mask will blur by the same amount as the object shifts from the predetermined position, but this will not cause difficulty in phase detection. do not have.

In the configuration shown in FIG. 8, the function of rotating the mirror is substituted by projecting and receiving light through a focusing lens.

In Figure 8, E is the human eye, Ef is the fundus, Ec is the cornea,
Ep indicates the pupil. Further, 1 is an objective lens, 2 is a photographic diaphragm, 3 is a negative focusing lens, 4 is a photographic lens, 5 is a shutter, and 6 is a photographic film, and these members constitute a photographing system. However, the objective lens 1 forms a single fundus image, and the focusing lens 3 and the imaging lens 4 jointly form this intermediate image on the film 6 again.

Next, 10 is an observation light source such as a tungsten lamp, 11 is a condenser mirror, 12 is a condenser lens, 13 is a photography light source such as a strobe tube, and 14
1 is a second condenser lens, and 15 is a ring slit plate. This ring slit plate 15 has an annular opening surrounding a central light shielding circle 15a. Further, the light source 10 and the light source 13 are connected to the first condenser lens 1.
2, the light source 13 and the ring slit plate 15 are conjugate with respect to the second condenser lens 14. 16 is a relay lens; 17 is a perforated mirror; the aperture of the perforated mirror has a size that does not block the light flux entering the aperture 2; In addition, the perforated mirror 17 and the ring slit plate 15 are made conjugate with respect to the relay lens 16, so that the light beam reflected by the perforated mirror 17 is transmitted to the objective lens 1.
The image forming position of the ring slit plate is arranged so that the aperture 2 is conjugate with respect to the objective lens 1. Note that when the working distance is appropriate, the image of the ring slit is set to match the position of the anterior segment of the eye, for example, the pupil Ep. The above 10 to 17 and the objective lens 1 constitute an illumination system.

Also, 20 is a quick return mirror, 21 is a field lens, and the field lens is mirror 2.
It is provided at a position conjugate with the film surface 6 with respect to 0.
22 is an optical path bending mirror; 23 is an eyepiece; the eyepiece 23 is for observing the fundus image on the field lens 21; Note that a television camera focusing on the image plane on the field lens may be provided instead of the eyepiece.

Next, the characteristic configuration of this embodiment will be explained. First, as shown in FIG. 9, the diaphragm 2 has an aperture 2a that restricts the light beam reaching the film 6, and a window 2b that has a filter that allows distance measurement light beams such as infrared rays to pass through, but completely blocks photographic light beams. and 2c. The aperture of the fundus camera is normally set to the cornea with respect to objective lens 1.
It becomes conjugate with Ec or pupil Ep, but windows 2b and 2
The outer edge of c is determined so that when the image of this aperture is projected onto the pupil, the outer edge of the window image is included in the pupil.

Next, 30a and 30b are mask illumination light sources, each of which is an infrared light emitting diode. 31 is the first
The projection mask shown in FIG. 0 includes linear slits 31a and 31b. 32 is a projection lens, 33 is a light receiving lens, and 34 is a half mirror. The half-mirror 34 is disposed at 45 degrees to the optical axis to bring the projection lens 32 and the light-receiving lens 33 into a coaxial relationship, and covers half of the optical path. Further, the half-mirror 34 is conjugate with the pupil Ep or its vicinity with respect to the intervening optical system.
35 is a small mirror that reflects infrared light and passes visible light, and has the function of optically coupling the projection/detection section and the optical system of the fundus camera. Reference numeral 36 denotes a detection mask shown in FIG. 11, which is provided with linear slits 36a and 36b at a slightly wider interval than in the case of FIG. 10, and this mask and the projection mask 36 are conjugate with respect to the half mirror 34. 37 is a photoelectric conversion element, 38 is a light source blinking control circuit, 39 is an AC amplitude phase detection circuit, 40 is a servo circuit that drives the focusing lens 3,
The phase detection circuit 39 is based on the light source control circuit 38.
The servo circuit 40 emits a signal to set the direction in which the focus should be moved, which is determined from the output indicating which light source is lit at each time and the output of the photoelectric conversion element 37 corresponding to the amount of incident light. Based on the signal, the focusing lens 3 is moved in the determined direction as long as the signal continues. It is assumed that the servo circuit 40 locks the focusing lens 3 at the current position based on the release signal.

The operation of the above device will be explained.

First, the observation light source 10 and the circuits 38, 39, 4
Drive 0. The control circuit 38 turns on the mask illumination light sources 30a and 30b alternately, and the slits 31a and 31b of the projection mask are alternately illuminated. The mark light beam emitted from the slit 31a or 31b is subjected to an imaging action by the projection lens 32, reflected by the half mirror 34, and further reflected by the small mirror 35 to form a slit image on the field lens 21, and then returned to the quick return. The slit image is formed again through the mirror 20, photographic lens 4, focusing lens 3, and aperture window 2b, passes through the objective lens 1, passes through one side of the pupil Ep, and is projected onto the fundus Ef. The light beam scattered and reflected by the fundus Ef exits the opposite side of the pupil Ep, and after forming a reflected image of the slit in the objective lens,
Passing through the aperture window 2b, the focusing lens 3,
Quick return mirror 20 via photographic lens 4
The light is reflected by the light beam, forms a slit image on or near the field lens 21, is reflected by the small mirror 35, enters the light receiving lens 33 through an optical path not covered by the half mirror 34, and has an imaging effect there. The received light is incident on the detection mask 36.

The images of the projection slits 31a and 31b alternately formed on the detection mask 36 are determined depending on the direction of deviation from the conjugate of the projection mask 31 and the fundus Ef, that is, the image of the projection mask 31 is formed in front of the fundus Ef. Depending on whether the image is formed later than the fundus Ef, the position of the detection slits 36a and 36b is shifted in the direction in which they are lined up. Increase, decrease, or equal amount in relation to lighting.

Since the photoelectric conversion element 37 outputs an electric signal according to the amount of incident light, the phase detection circuit 39 determines the direction in which the focusing lens 3 should be moved based on the output and the lighting period of the mask illumination light source, and the servo circuit determines the direction in which the focusing lens 3 should be moved. 40 to move the focusing lens 3. When the focusing lens 3 reaches a certain position, the output signal of the photoelectric conversion element 37 becomes constant regardless of whether the mask illumination light source blinks, and the focusing lens 3 remains at that position. The camera operator finely adjusts the direction of the camera while looking through the eyepiece 23 so that the desired part of the fundus falls within the viewfinder's field of view. Even if the focus changes, the servo circuit 40 works to quickly refocus. It is something.
Therefore, when the operator confirms the field of view and releases the camera, the photographing light source 13 is turned on, the quick return mirror 20 is raised, and the shutter 5 is opened.
Film 6 is exposed.

According to the present invention described above, it is possible to measure the distance to an object located at any position, and since the detection is performed using the same light receiving element, it is possible to eliminate the drawbacks caused by the performance of the element. This has the effect of enabling precise focus adjustment.

[Brief explanation of the drawing]

Fig. 1 is a sectional view of a basic embodiment of the present invention;
3 and 3 are respectively plan views of the constituent elements, and FIGS. 4 and 5 are diagrams showing the relationship between the projection slit reflected image and the detection slit, respectively. 6. FIGS. 1 and 2 are lighting waveform diagrams of the mask illumination light source. 7. FIGS. 1, 2, and 3 are output waveform diagrams of the photoelectric conversion element. FIG. 8 is a sectional view of another embodiment. FIG. 9, FIG. 10, and FIG. 11 are plan views of the constituent elements. In the figure, L is the baseline length, B is the projection mask, B ₁ and B ₂
is the slit or mark, D is the object to be measured, F
is a scanning mirror, H is a detection mask, H ₁ and H ₂ are slits or detection areas, 1 is an objective lens, 2 is an aperture, 3 is a focusing lens, 31 is a projection mask, 34 is a half-mirror, and 36 is a detection mask , 37 is a photoelectric conversion element or a light receiving element.

Claims (1)

[Scope of Claims] 1. Means for alternately projecting a plurality of marks substantially spaced at predetermined intervals in the baseline length direction onto an object, and reflected light from the object directed in a direction different from the projection direction of the marks. a light-receiving means for receiving light with a single light-receiving element through a plurality of detection areas arranged in the baseline length direction at intervals different from the intervals between images of the marks reflected by the object; scanning means for moving a predetermined optical member in the optical path so that the image of the mark is displaced in the base line length direction; A distance measuring device characterized by having means for calculating a position. 2. The object according to claim 1, wherein the object is the fundus of the eye to be examined, and the light flux from the mark at the anterior segment of the eye to be examined and the light flux reflected from the fundus of the eye to be examined and directed toward the light receiving element are separated. Ranging device. 3. The distance measuring device according to claim 1, wherein the scanning means mechanically changes the optical axis by rotating a mirror in the optical path from the object to the light receiving element. 4. The distance measuring device according to claim 1, wherein the scanning means moves a focusing lens, which is shared by an optical path for projecting the mark and an optical path from the object to the light receiving element, in the optical axis direction.