JPS61240213A - Focus detecting device - Google Patents

Abstract

PURPOSE:To constitute the titled device so that an error of a defocus quantity does not become large remarkably, even if a full-aperture F-value of an image pickup lens has been changed, by setting a reference corresponding F-value to become a reference for correcting a distortion, to a value corresponding to an effective aperture diameter which is smaller than an effective aperture diameter which has been given actually to an image re-forming lens. CONSTITUTION:Inter-element pitches Pa1, Pa2,... and Pb1, Pb2... are determined so that a distortion which an image re-forming optical system has is corrected, when a value of about FRO=3.3 or FRO=4 of a reference corresponding value has been given as an effective aperture diameter of an image re-forming lens 6 and 7 for giving an effective aperture diameter corresponding to the corresponding aperture F-value FR=2.8, to the image re-forming lens 6 and 7. Even if the aperture F-value FM of an image pickup lens 1 is varied between 1.4-5.6, a defocus quantity error DELTA is contained in an allowable range, and a focus can be detected with a high accuracy.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a focus detection device for optical equipment such as a camera. The present invention relates to a focus detection device that refocuses an image onto a photoelectric conversion element array using an optical system and detects the focus of a main focusing optical system using output signals from each of seven rays.

(Background of the Invention) Referring to FIG. 2, in the optical system of this type of focus detection device, first and second portions 2.
The light beams that have passed through the lens 3 form first and second primary optical phenomena in the vicinity of the main imaging surface 4 of the photographic lens l as the main imaging optical system.

Each of these -order optical images is transferred via the field lens 5 to the photoelectric conversion element arrays SA and SB arranged on the reimaging surface 8 by the first and second reimaging lenses 68 and 7. It is re-imaged as a secondary light phenomenon.

If the open F value FM of the photographing lens l is small and the lens l is sufficiently bright, the detection light flux projected onto the reimaging surface 8 is regulated by the apertures 6a and 6b of the reimaging lenses 6 and 7. The effective aperture diameter of the pair of retiring threads determined by the apertures 6a and 7a is determined by the field lens 5 at the exit pupil position of the photographing lens 1, which is disposed at a distance #IL from the main object plane 4. Projected approximately conjugately. here,
The F value FR (referred to as equivalent open F value) determined by the outer light flux r1 of the re-imaging lens 6 and the outer light flux r2 of the re-imaging lens 7 that converge the detection light flux on the exit pupil is expressed as follows: FR=- Expressed as , if FR≧FM, the effective aperture diameter of the re-imaging lenses 6 and 7 can be used over the entire area, and a decrease in the effective detected light flux due to "vignetting" caused by the photographing lens 1 can be prevented. can. The imaged light beam in Fig. 2 shows such a case, and the center point (A) of the main imaged surface 4
are reimaging planes 8 by reimaging lenses 6 and 7, respectively.
It is imaged at the positions (E1) and (E2) above in a substantially point image state. In addition, the point (b) at the end of the main image plane 4 is slightly expanded by the re-imaging lenses 6 and 7 around the positions of (row 1) and (row 2) on the re-imaging plane 8. It is visualized as an image. Such spread is caused by the presence of the field lens and distortion aberration of the re-imaging optical system. In general, the positions (row 1) and (row 2)
It can be treated as if a point image is formed in the image.

However, the distances 191b between the positions (E1) and (Row1) are not equal. In other words, if a distortion aberration exists in the re-imaging optical system, the ratio of the distance between any two points on the main imaging surface 4 to the corresponding distance between two points on the re-imaging surface 8, that is, the magnification differs from place to place. Therefore, if the pitch between the elements of the photoelectric conversion element array is kept constant, an error will be included in the amount of defocus obtained from the output of the photoelectric conversion element array.

Therefore, the applicant first filed Japanese Patent Application No. 57-153632 (
Japanese Patent Laid-Open No. 59-42507) proposes a focus detection device that eliminates errors caused by distortion in a reimaging optical system.

That is, in that device, the pitch between the elements of the pair of photoelectric conversion element arrays is changed according to the magnification according to the distortion aberration, that is, the amount of distortion, depending on the position of each photoelectric conversion element, and the pitch between the elements of the pair on the main object plane 4 is changed. The aerial images of the photoelectric conversion element arrays are made to completely overlap.

However, when the open F-number FM of the photographic lens l becomes large, a part of the light beam incident on the re-imaging optical system is "eclipsed" by the aperture of the photographic lens l, so the effective aperture diameter of the re-imaging optical system is It cannot be used as a whole, and the spread of the effective detection beam is reduced. Therefore, the distortion aberration of the reimaging optical system is substantially changed, and the pitch between the elements of the array described above is not necessarily optimal.

Referring to FIG. 3, the image on the main imaging plane 8 is a slightly expanded and blurred image as described above, but due to the ``vignetting'' of the effective light beam by the photographic lens 1, the center of the blurred image is The position changes slightly. These amounts of change are shown as δa and δb, respectively, in Figure 3, but since they change in opposite directions, they do not cancel each other out, and the error amount is (δa + δb).
becomes. Here, (δa + δb) is about 10 JLm! However, the amount of defocus is approximately 50 to 200 pm, and focus detection accuracy is reduced.

(Object of the Invention) An object of the present invention is to provide a focus detection device capable of solving the above conventional problems and detecting the focus detection state within an appropriate error regardless of the size of the open F value of the main focusing optical system. Our goal is to provide the following.

(Summary of the Invention) The present invention obtains a relative shift amount of a secondary optical image formed by a main imaging optical system based on outputs from a pair of photoelectric conversion element arrays onto which the primary optical image is projected. , thereby applied to a focus detection device that detects a focus detection state. In the present invention, the photoelectric conversion element arrays are arranged at the following arrangement pitch, so that even if the open F value of the main imaging optical system changes, each of the pair of photoelectric conversion element arrays on the main imaging plane The aerial images are made to overlap in an acceptably generally consistent manner. That is, the arrangement pitch is determined according to the amount of aberration when the re-imaging optical system is given an effective aperture diameter smaller than the first effective aperture diameter actually given to the re-imaging optical system.

(Embodiment) FIG. 1 shows an embodiment of the present invention. Elements similar to those in FIG. 2 are given the same reference numerals and will be described below.

In the following explanation, it is assumed that the open F value FM of the photographic lens l is changed from 1.4 to 5.6 depending on the type of photographic lens. The effective aperture diameter is set to such a value that the detection light flux of the re-imaging optical system is not "eclipsed" by the photographing lens 1 when the open F-number FM of the lens 1 is 2.8. Therefore,
Equivalent open F value F of the re-forming optical system for its effective aperture diameter
R can be treated as 2.8.

On the other hand, the pitch between the photoelectric elements of the photoelectric conversion element arrays SA and SB in FIG.
2-... is determined as follows.

That is, in the re-imaging optical system (re-imaging lenses 6 and 7) with the aforementioned equivalent aperture F value F R = 2.8, the effective aperture diameter is F-number FRO (referred to as reference aperture F-number) = 3.3. is corrected, and the inter-element pitch is determined so that the aerial images of the pair of photoelectric conversion element arrays SA and SB on the main imaging plane 4 coincide and overlap.

FIG. 4 shows the equivalent open F-number FR of the re-imaging lenses 6 and 7.
When is set to 2.8 as in the above example,
Correction of inter-element pitch is based on F value FRO = 2.8
．． ．． 3.3.4 and 5.8 respectively, the open F value FM of the photographing lens 1 is set to 1.4.
This shows how much error is included in the defocus amount determined according to the output of the photoelectric conversion element array when the value is changed from 5.6 to 5.6. That is, the horizontal axis in FIG. 4 represents the open F-number FM of the photographic lens 1, and the vertical axis represents the defocus amount error Δ. That is, FIG. 4 shows that the value of the defocus amount varies in the range of 0 to Δ depending on the position on the photoelectric conversion element where a rod-shaped object is imaged, for example. In other words, the characteristic curve in the figure corresponds to the maximum amount of error. Characteristic curves A, B, C and D in FIG. 4 will be explained below.

1) Characteristic curve A Take the reference equivalent F value FRO equal to the equivalent open FmFR
If the pitch between the elements is determined so that the distortion due to RO=2.8 is corrected, the maximum aperture of the photographing lens l is F4.
If fI F M is 2.8 or less, the defocus amount does not include an error. However, the open F value of the photographic lens
M=5. In I3, the maximum point of the error variation range deviates from the allowable range depending on the depth of field.

2) Characteristic curve B If the pitch between the elements is determined so that the distortion due to the reference equivalent F value F RO = 3.3 is corrected, the defocus amount will be The error Δ is zero, but when FM>3.3, the defocus amount error Δ increases to the positive side and varies from zero to the range shown by characteristic curve B (hatched area), and when FM<3.3 The detection light flux of the re-imaging optical system increases too much and the error Δ increases to the negative side. However, the error Δ in the minimum open F-number FR=1°4 and the maximum open F-number FR=5.8 of the photographic lens 1 is included in the allowable range of the depth of field.

3) Characteristic curve C Standard equivalent F@! If the pitch between the elements is determined so that the distortion due to FRO=4 is corrected, the photographing lens l
When the open F value FM is between 1.4 and 5.6, the defocus amount error Δ is included in the allowable range as in the characteristic curve B.

4) Characteristic curve standard equivalent F value FRO=5. If the pitch between the elements is determined so that the distortion caused by I3 is corrected, the defocus amount error Δ is zero when the photographing lens 1 is fully open FfHFM=5.8. However, when the open F value FM<5.8, the defocus amount error Δ increases to the negative side, and F≦2,
8, the depth of field falls outside the allowable range.

Therefore, as in this embodiment, the re-imaging lenses 6 and 7 are given an effective aperture diameter equivalent to the equivalent open F value F R = 2.8, and the effective aperture diameter of the re-imaging lenses 6 and 7 is Standard equivalent F value FRO= 3.3 or FRO=
If the inter-element pitch is determined so that the distortion aberration of the re-imaging optical system is corrected when a value of about 4 is given,
Open F of photographic lens 1 (i FM is 1.4 to 5.6
Even if the defocus amount error Δ changes between the two, the defocus amount error Δ is within the permissible range, and accurate focus detection can be performed.

Note that the sum of the error amounts δa and δb (δa
+δb) and the defocus amount error Δ in FIG. 4, the following equation approximately holds true. Figure 4 is obtained from the following equation.

(However, FM>FRO) Here, FRO is equal to the reference equivalent F value used to define the inter-element pitch in 1) to 4) above.
be.

In summary, focus detection accuracy is improved by determining the reference equivalent F-number FRO, which serves as a reference for determining the inter-element pitch, as follows.

FR<FRO<FMmax Here, FR is the actual equivalent aperture F value of the re-imaging lenses 6 and 7, and FMmax is the aperture F value of the target photographing lens 1.
It is the one with the largest value.

-Most of the interchangeable lenses for eye reflex cameras have an aperture of 5.
．． Therefore, if the FMma violet is selected to be about 5.8, consideration will be given to most interchangeable lenses. In reality, there are some photographic lenses with an open F value of 8 or 11, so FMmax is selected to be a value of about 5.6 to 11.

Furthermore, if the ``vignetting'' becomes large, FMmax
It is preferable that ≦2XFR. - As a condition for forming a film, the standard equivalent F-number FRO used for aberration correction is preferably about FR<FRO≦1-ball FMmπ with respect to the equivalent open F-number FR of the re-imaging optical system, and the center value is used.

A value of about FRO=RX RXFMmax is most effective. Substituting the case of FMmax = 2XFR into this, the above two equations become FR<FRO≦1.4X, respectively.
FR, and the center value is FRO=1.2. Since the value corresponds to an effective aperture diameter smaller than the effective aperture diameter given to the re-imaging lens, even if the aperture F value of the photographic lens changes, the defocus amount error will not become significantly large, and
Never deviate from the depth of field.

[Brief explanation of drawings]

Figure 1 is a diagram showing an optical system that is an embodiment of the present invention, Figure 2 is a diagram showing an optical system that is an embodiment of the present invention.
Figure 3 and Figure 3 are diagrams showing the state of the luminous flux. Figure 2 shows the case where the aperture f-number of the photographing lens is small, Figure 3 shows the case when it is large, and Figure 4 shows the defocus amount error and the aperture of the photographic lens. It is a graph showing the relationship with the F value FM using the reference equivalent F value FRO as a parameter.

Claims (1)

[Claims] a pair of photoelectric conversion element arrays in which a large number of photoelectric conversion elements are arranged; and a re-imaging optical system that projects a secondary optical image of the primary optical image formed by the main imaging optical system onto the pair of photoelectric conversion element arrays, respectively. and a focus detection device that detects a focus adjustment state based on the relative positional relationship of a pair of secondary light phenomena on the array obtained according to the output from the photoelectric conversion element array, wherein the refocusing optical The effective aperture diameter of the system is set to a first aperture diameter, and the photoelectric conversion elements are arranged at an arrangement pitch corresponding to the amount of aberration when an effective aperture diameter smaller than the first aperture diameter is given to the refocusing optical system. A focus detection device characterized by an arrangement of each.