JPS5995504A - Focusing position detector - Google Patents

Abstract

PURPOSE:To vary precision characteristics of decision on a focusing state by providing a correcting means for optical path length which varies the length of an optical path of final split light and holding the direction of incidence to an array sensor almost the same. CONSTITUTION:Image-forming luminous flux 21 transmitted through the transmission mirror part of a quick return mirror is split into three mutually parallel pieces of luminous flux by the half-mirror 9 of a light splitter 24 and projected on the array sensor 12, wherein a sensor 122 is placed on an expected image- formation surface and sensors 121 and 123 are at equal distance from it to perform normal focusing detection. When the light splitter 24 is moved slightly, luminous flux transmitted through a beam splitter 35 is reflected by a reflecting surface 36 of a prism to enter the sensor 123 with different optical path length. For this purpose, the output F3 of the sensor 123 beyond a focusing range 14 is viewed to increase greatly the range wherein a photographic lens is moved out and in, deciding on the focusing state.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a focusing position detection device suitable for a single-lens reflex camera. This invention relates to a focus detection device that detects the in-focus state by comparing blurs at six locations, for example, COD image sensors, which are provided at a total of six locations, including one location and two locations equidistant from each other before and after it.

JP-A-55-155308 has been proposed as a focus position detection device suitable for single-lens reflex cameras.

As shown in Fig. 1, this device is equipped with three light receivers 4, 5, and 6 for detecting the image forming state at distant positions, at approximately the same distance in front and behind the planned image forming surface. The in-focus state is determined based on the output signal of.These light receivers are, for example, line sensors such as COD array sensors.In this line sensor, a sensor array is formed on the same plane.

Furthermore, as a light splitter suitable for such a focusing position detection device, Japanese Patent Application Laid-Open No. 57-23911 and Japanese Patent Application Laid-Open No. 57-416
09 has been proposed. In other words, it is a light splitter as shown in FIG. In the figure, 7 is a submirror provided behind the quick return mirror (not shown), 8 is a light splitter, 9-1, 9-2 are half mirrors, and 9-5 is a total reflection mirror. It's a mirror. In addition, 10 is a cover glass, and 11 is 12-1 to 12
-3 is a silicon substrate on which each line sensor light receiver is provided.

Such a focus detection device is disclosed in the Japanese Patent Application Laid-open No. 55-15 mentioned above.
By electrically processing the output signal from each light receiver as described in 5608, an output value corresponding to the defocus amount as shown in FIG. 6 can be obtained. In the figure, the horizontal axis in degrees Celsius represents the amount of lens protrusion, and the vertical axis represents the output from each light receiver after processing. The output from each light receiver changes as Fl, 1''2. is correctly distinguished, but in the region 14, the six outputs cannot be distinguished, making it impossible to determine the correct in-focus state.

FIG. 4 shows an apparatus in which the optical path length difference between the sensors 41 and 5 and the optical path length difference between the sensors 5 and 6' are large. In such a device, as before, the output values F1', F2', and FB' obtained by processing the lens protrusion amount and the signals from each light receiver are illustrated in FIG. 5. F2 corresponds to FIG. 6 and has the same symbol. In this figure, since the output value Fs/ is large in the 14th region as well, the in-focus state is determined as 5. However, since the levels of F1' and F3' are low in a region close to the position FvC of the photographing lens at the time of focusing, it has a characteristic that the accuracy of determining the in-focus state becomes low.

An object of the present invention is to provide a focus position detection device 7 in which the accuracy characteristics of determining the focus state can be changed.

This objective is achieved by an optical path length correction means that can change the optical path length by varying the optical path length of the final divided light and maintain the same direction of incidence on the array sensor.

The present invention will be explained below using the drawings. FIG. 6 is a diagram showing the first embodiment, in which 21 is a light beam coming from a photographing lens (not shown), and these light beams are reflected by a quick return mirror 22.
Most of the light is directed towards the viewfinder system. The light that has passed through a part of the central part of the quick return mirror 22 is directed to a light splitter 24 by a sub-mirror 23, and is split by this light splitter into six mutually parallel beams. Each six-element bundle is given an optical path length difference.

25 receives six light beams divided by array sensors arranged on the same plane.

FIG. 7 is a diagram showing the light splitter 24 of FIG.
A light splitter 4 is provided at an angle of 90 degrees with respect to the VC, and the imaging light transmitted through the beam splitter 65 is reflected by the reflective surface filter 6 of the prism, and then reflected by the beam splitter 65 again. .

The state when the array sensor 12-1 is placed on the planned image forming plane or a plane conjugate thereto, and the array sensors 12-1, 12-=3 are placed an equal distance away from it, and normal focus detection is performed. 7 is shown.

Figure 8 shows array sensors 12-1, 12-2, 12-
After performing signal processing on the output of F1.s, the output F1. F2. F3 is shown, and the coordinates are taken in the same way as in Figure 6. F represents the position of the photographing lens at the time of focusing. 16 is the focusable range, and 14 is outside the focusable range.

FIG. 9 shows that in FIG. 8, when the photographing lens is outside the focus detectable range 14, the light splitter is moved parallel to the sensor surface, and the imaging light flux entering the array sensor 12-3 in FIG. This shows where the optical path length has been extended.

Figure 10 shows 12-1, 12-2, 12-3 at that time.
shows the output of At this time, look at the output of F3,
This shows that it is possible to judge whether to move the photographic lens to extend or retract. After moving the photographic lens in this manner and bringing it within the range 16, focusing can be performed again by adjusting the positional relationship shown by the array sensor 25 and the light splitting prism 24.

In Figure 11.12, the shaded prism 40 of the light splitting prism 24 is movable and moves parallel to the beam splitter 9-3.
2-3 is an example of a light splitter that can continuously vary the optical path length of the input imaging light.

That is, FIG. 11 shows a normal position, in which array sensor 12-2 is placed on the intended image plane or a plane conjugate thereto, and array sensors 12-1 and 12-3 are placed in a plane that is equal to or greater than array sensor 12-2. It is recommended that they be placed at positions separated by the difference in optical path length. Array sensor-12
The output is as shown in FIG. When the photographing lens is at position 14 and F1 to F3 are indistinguishable and in the range where focus cannot be detected, it enters the sixth array sensor 12-5 using the method described above, as shown in Fig. 12. Optical path length difference of imaging light 2
When the output of the array sensor 12 becomes as shown in FIG. 10, focus detection becomes possible as in the previous embodiment.

(Refractive index of the optical path prism of the imaging light entering the sixth array sensor 12-3) Also, in the same arrangement as in Fig. 11.12, the light receiver 12-1
．． 12-2 is placed at an equal distance from the expected imaging position or a position conjugate thereto, and 12-3 is located at a position further extended than 12-2. By increasing the optical path length difference of the imaging light entering the array sensor 12-3, the focus detection range can be expanded.

As explained in detail above, by using the prism of the present invention, when the photographing lens is outside the focus detection range,
Extending the optical path length of the imaging light entering the array sensor of 6,
In addition, by making the light incident from the same direction, it is possible to extend the lens capable of signal processing in the blur detection method, and to greatly expand the convergence area.

[Brief explanation of drawings]

Fig. 1 is a diagram showing a conventional focusing position detection device 2, Fig. 2 is a diagram showing a conventional light splitter, and Fig. 6 is a diagram showing the signal output and lens extension amount in the focusing position detection device of Fig. 2. Graph 1 shows the relationship between the output signal and the lens extension amount in the conventional focusing position detecting device shown in Fig. 4. 6 is a diagram showing an outline of the focusing position detection device of the present invention, FIG. 7 is a diagram showing details 2 of the light splitter of FIG. 6, and FIG. Figure 9 shows the state in which the light splitter shown in Figure 7 has been moved. Figure 10 shows the sensor array output and focus detection in the state shown in Figure 9. FIGS. 11 and 12 are diagrams showing a possible range. FIGS. 11 and 12 are diagrams showing a light splitter having a configuration different from that in FIG. 7. In the figure, 21 is an imaging light beam, 26 is a submirror 22 is a quick return mirror, and 24 is a light splitter 25
is an array sensor. Applicant Canon Co., Ltd. Agent Gi Marushima −, (−−11] 4th Kasumi? )−

Claims (1)

[Claims] The light beam from the imaging optical system is divided into at least two parts by a light splitter.
At the same time, the divided light beams are given different optical path lengths and are made to enter each of multiple array sensor arrays arranged on the same plane, and the read signals from each array sensor array are input to an arithmetic processing circuit and focused. In the position detecting device, the device has an optical path length correction means that substantially extends the optical path of the final divided light divided by the light splitter and maintains the same direction of incidence on the array sensor. fzr: A focusing position detection device that uses % characteristics.