JP4795018B2 - Autofocus imaging optical system - Google Patents

Description

  The present invention relates to an autofocus imaging optical system that has a branching optical system in an optical path and performs autofocus using a branched light beam.

  Conventionally, various methods have been proposed as an autofocus technique in a photographing apparatus such as a still camera or a video camera. In particular, Patent Documents 1 to 3 propose lenses and imaging devices in which a branching optical system is disposed in the optical path and an autofocus detection unit is provided in the branching optical path.

  As in these patent documents, in an imaging system that detects an in-focus state by a branched light beam from a branching optical system and performs autofocusing, in principle, the optical system on the focus detection side and the optical system on the imaging side after the branching optical system It is necessary to make the relationship between and constant. As a result, the following items are achieved, and appropriate focusing control is possible.

  (A) The relationship between the detection value from the focus detection means and the focus state on the imaging surface is kept constant.

  (B) When considering auto-focusing on the subject in the periphery of the screen, the positional relationship of the distance measurement frames corresponding to a predetermined position on the imaging surface is kept constant.

  Furthermore, it is desirable that the relationship between the unit operation amount of the focus movement group and the focus change amount be a predetermined relationship. As a result, high-speed and high-precision autofocus can be achieved.

  (C) The relationship between the unit operation amount of the focus movement group and the focus change amount is set as a predetermined relationship, and the operation speed and position control accuracy of the focus movement group can be defined based on this relationship.

JP-A-55-76312 JP-A-9-274130 JP 2002-365517 A

  However, generally, in an imaging optical system for a television camera, a focal length conversion optical system that can be inserted into and removed from the imaging optical system is arranged. Since the focal length converting optical system is inserted into and removed from the optical path, the relationship between the focusing detection side optical system and the imaging side optical system after the branching optical system cannot be maintained. There is a problem that cannot be achieved.

  Further, there is a problem that the relationship between the unit operation amount of the focus movement group and the focus change amount cannot be maintained by inserting / removing the focal length conversion optical system, and (c) cannot be achieved.

  An object of the present invention is to solve the above-mentioned problems, and in an imaging optical system that performs focus detection by branching an incident light beam in the imaging optical system, various imaging optical systems of high accuracy and high speed are provided. An object of the present invention is to provide an autofocus imaging optical system that can cope with the use situation.

In order to achieve the above object, an autofocus imaging optical system according to the present invention includes a focus movement group, an optical path branching optical system disposed in an optical path on the image side of the focus movement group, the focus movement group, and the optical path. A focal length conversion optical system that is detachably disposed between the branching optical systems, a focus detection unit that detects a focus state by the focus movement group using a branched light beam from the optical path branching optical system, and An autofocus imaging optical system having a calculation unit that performs an autofocus calculation based on an output of a focus detection unit, and a drive control unit that drives and controls the focus movement group based on the output of the calculation unit, By inserting the focal length conversion optical system into the optical path between the focus moving group and the optical path branching optical system, the focal length conversion magnification is β2, and the focal length conversion optical system is The movement amount of the focus movement group with respect to a predetermined amount of focus change in a state where it is not inserted in the optical path between the focus movement group and the optical path branching optical system is X, and the focal length conversion optical system is the focus movement X ′ represents the amount of movement of the focus movement group with respect to the predetermined amount of focus change in the state of being inserted into the optical path between the group and the optical path branching optical system, and the focal length conversion optical system is referred to as the focus movement group. The focusing accuracy on the detection side when not inserted in the optical path between the optical path branching optical system is Pb, and the focal length conversion optical system is in the optical path between the focus moving group and the optical path branching optical system. When the detection-side focusing accuracy in the state of being inserted into is Pb ′ ,
0.8 <β2 ² · X ′ / X <1.2
0.9 <(Pb ′ · β2) / Pb <1.1
It is characterized by satisfying.
Further, as the focal length conversion optical system is inserted into and removed from the optical path, the calculation means switches a driving amount of the focus movement group with respect to a signal from the focus detection means.
Furthermore, the control accuracy of the drive control means for the signal from the focus detection means is switched as the focal length conversion optical system is inserted into and removed from the optical path.
According to another aspect of the present invention, there is provided a photographing apparatus comprising: the autofocus imaging optical system described above; and an imaging unit disposed on the image side of the autofocus imaging optical system.

  With the autofocus imaging optical system according to the present invention, it is possible to appropriately set the focus group drive amount with respect to the focus detection output and the detection accuracy of the focus detection means, which is appropriate regardless of whether the focal length conversion optical system is inserted or removed. Auto focus can be performed.

The present invention will be described in detail based on the embodiments shown in the drawings.
FIG. 1 is a schematic view of an imaging optical system described prior to the embodiment. On the optical path of the incident light, the focus moving group 1, the focal length conversion optical system 2 that can be inserted into and removed from the optical path, the branching optical system 3, the imaging side partial optical system 4a, and the imaging means 5 are sequentially arranged. The detection-side partial optical system 4b and the focus detection element 6 are arranged in the branching direction.

Before insertion of the focal length conversion optical system 2 into the optical path, the imaging magnification of the focus moving group 1 is β1, the imaging magnification of the imaging side partial optical system 4a is β4a, and the imaging magnification of the detection side partial optical system 4b is β4b. Then, the imaging side imaging magnification βa and the detection side imaging magnification βb are expressed by the following equations.
βa = β1 · β4a (1)
βb = β1 · β4b (2)

Accordingly, the imaging magnification ratio Rβab of the detection-side imaging magnification βb with respect to the imaging-side imaging magnification βa is expressed by the following equation. The imaging magnification ratio Rβab is the imaging-side partial optical system 4a after the branching optical system 3, and the detection side It is determined by the imaging magnifications βa and βb of the partial optical system 4b.
Rβab = βb / βa = β4b / β4a (3)

Next, assuming that the diagonal imaging range of the imaging unit 5, that is, the image size is S0, and the range that the focus detection element 6 included in the focus detection element 6 can take the diagonal distance measurement frame is A0. The ratio Ras of the focus detectable range with respect to the image size S0 is expressed by the following equation.
Ras = (A0 / S0) .Rβab (4)

Here, as a condition of the ratio Ras of the focus detectable range, it is desirable that the range is the following formula.
0.3 <Ras <1.1 (5)

  In other words, if the upper limit of the expression (5) is exceeded, the range A0 that the distance measurement frame can take will protrude beyond the screen, and it will not be possible to focus properly. If the lower limit of the expression (5) is exceeded, the range A0 that the distance measurement frame can take on the screen is limited, and appropriate framing is hindered.

When optical magnification conversion is performed by the focal length conversion optical system 2, if the conversion magnification of the focal length conversion optical system 2 is β2, imaging on the photographing side when the focal length conversion optical system 2 is inserted in the optical path The magnification βa ′ and the detection-side imaging magnification βb ′ are respectively expressed by the following equations.
βa ′ = β1, β2, β4a (6)
βb ′ = β1, β2, β4b (7)

Therefore, the imaging magnification ratio Rβab ′ of the detection-side imaging magnification βb ′ with respect to the imaging-side imaging magnification βa ′ after insertion into the optical path of the focal length conversion optical system 2 is expressed by the following equation.
Rβab ′ = βb ′ / βa ′ = Rβab (8)

  Since the imaging magnification ratio Rβab does not change before and after the insertion of the focal length conversion optical system 2, the ratio Ras of the focus detectable range does not change from the equation (4), and is measured by inserting and removing the focal length conversion optical system 2. The range A0 that the distance frame can take does not change.

  As shown in FIG. 2, the distance measurement frame is a system that uses the entire range of the focus detection element 6, a system that continuously moves and selects an arbitrary range as shown in FIG. 3, and a discrete area shown in FIG. Any of the methods of selecting all or a part of these may be used. Note that the range A0 that the distance measurement frame can take is defined by the length dimension on the image plane on the focus detection side, and includes any of horizontal, vertical, and diagonal dimensions of the screen unless otherwise specified.

When there is a focus shift amount ΔSa on the imaging side, the detection-side focus shift amount ΔSb is proportional to the square of the detection-side imaging magnification ratio Rβab with respect to the imaging side and is expressed by the following equation.
ΔSb = ΔSa · Rβab ² (9)

  Therefore, if the imaging magnification ratio Rβab is known, the focus shift amount ΔSa on the imaging side can be obtained by measuring the focus shift amount ΔSb on the detection side.

When the imaging-side focus change amount with respect to the unit movement amount of the focus movement group 1 is ΔFa before the focal length conversion optical system 2 is inserted, the detection-side focus change amount ΔFb is expressed by the following equation.
ΔFb = ΔFa · Rβab ² (10)

Accordingly, the drive amount X of the focus movement group 1 necessary for focusing is expressed by the following equation.
X = −ΔSa · ΔXa = −ΔSb · ΔXb (11)

  However, it is expressed by ΔXa = 1 / ΔFa and ΔXb = 1 / ΔFb, and the focus shift amount ΔSb on the detection side is measured, and the focus is controlled by the drive amount X based on the equation (11), thereby achieving high speed and high accuracy. Autofocus can be achieved.

When the focal length conversion optical system 2 is inserted into the optical path and optical magnification conversion is performed, the focus change amount ΔFb ′ on the detection side after insertion of the focal length conversion optical system 2 is expressed by the following equation.
ΔFb ′ = ΔFa · β2 ² · Rβab ² = ΔFb · β2 ² (12)

Accordingly, the drive amount X ′ of the focus movement group 1 after the insertion of the focal length conversion optical system 2 is expressed by the following equation.
X ′ = − ΔSb / ΔFb ′ = X / β2 ² (13)

In order to avoid the focus drive amount per detection value from changing before the focal length conversion optical system 2 is inserted, the drive amount X ′ is preferably in the range of the following equation.
0.8 <β2 ² · X ′ / X <1.2 (14)

  Thereby, focusing control can be maintained substantially equal without depending on the insertion / removal of the focal length conversion optical system 2.

When the minimum circle of confusion with respect to the imaging means 5 is δ and the aperture value (F number) of the imaging optical system is FNo, the focal depth df on the imaging side is expressed by the following equation.
df = 2 · FNo · δ (15)

Prior to insertion of the focal length conversion optical system 2 into the optical path, the relationship between the focusing accuracy Pa required on the imaging side and the detection side detection accuracy Pb is expressed by the following equation using the square of the imaging magnification ratio Rβab. .
Pb = Pa · Rβab ² (16)

Further, when the detection-side focusing accuracy Pb is a value proportional to the focal depth df, the following equation is obtained.
Pb = CP · df · Rβab ²
= CP ・ 2 ・ FNo ・ δ ・ Rβab ² (17)

However, CP is a constant, and the value of this constant CP is preferably in the range of the following equation. By setting the value of this constant CP, the detection-side focusing accuracy Pb and the focal depth df are arbitrarily set. It becomes possible.
0.1 <CP <1.0 (18)

The F number FNo ′ of the imaging optical system in a state where the focal length conversion optical system 2 is inserted in the optical path changes with respect to the F number FNo before insertion, and is expressed by the following equation.
FNo ′ = FNo · β2 (19)

As described above, the imaging magnification ratio Rβab does not change due to the insertion / removal of the focal length conversion optical system 2 and is expressed by the following equation.
Rβab ′ = Rβab (20)

Therefore, the detection-side focusing accuracy Pb ′ after insertion of the focal length conversion optical system 2 is expressed by the following equation from equations (17), (19), and (20).
Pb ′ · β2 = Pb (21)

In order to make the detection-side focusing accuracy Pb by insertion / removal of the focal length conversion optical system 2 substantially equal, it is desirable to set the range as in the following equation.
0.9 <(Pb ′ · β2) / Pb <1.1 (22)

  FIG. 5 shows a configuration diagram of the embodiment. In the optical path of the incident light, a focus moving group 1, a focal length conversion optical system 2 that can be inserted into and removed from the optical path, a branching optical system 3, a relay lens group 11, and an imaging unit 5 are arranged, and the branching direction of the branching optical system 3 A focus detection means 12 having a focus detection element 6 is arranged in the. The output of the focus detection means 12 is connected to the calculation means 13, and the output of the calculation means 13 is connected to the drive means 14 that drives the focus movement group 1. The calculation means 13 is connected to the output of the detection means 15 that detects insertion / removal of the focal length conversion optical system 2. Note that the focal length conversion magnification β2 of the focal length converting optical system 2 in the embodiment is 2.0.

The focus detection unit 12 outputs a detection value based on the light beam branched by the optical path branching optical system 3, and the focus movement group 1 is driven and controlled by calculation of the calculation unit 13 to perform autofocus. When the focal length conversion optical system 2 is inserted into the optical path, the ratio Ras ′ of the focus detectable range to the imaging range is expressed by the following equation.
Ras' = Ras (23)

  The distance measurement possible range on the screen does not change before the insertion, and in this embodiment, the distance measurement possible range does not change due to the insertion / removal of the focal length conversion optical system 2.

When the focal length conversion optical system 2 is inserted, the detection-side focus change amount ΔFb ′ is expressed by the following equation from the equation (12).
ΔFb ′ = 0.25 · ΔFb (24)

Since this focus displacement amount ΔFb ′ changes with respect to that before insertion of the focal length conversion optical system 2, the focal length conversion optical system is obtained by setting the drive amount X ′ of the focus movement group 1 after insertion to the following equation. Equivalent focus control is achieved before and after 2 insertion / removal.
X ′ = 0.25 · X (25)

  In this embodiment, δ = 0.01 mm, Rβab = 1.0, and CP = 0.25, satisfying the condition of the equation (18) and enabling proper focusing control.

When the focal length conversion optical system 2 is inserted, the F number FNo ′ of the image forming optical system changes with respect to the F number FNo before insertion and becomes the following expression.
FNo '= 2.0 ・ FNo (26)

Before and after insertion / removal of the focal length conversion optical system 2 by setting the focus accuracy Pb ′ on the detection side at the time of insertion of the focal length conversion optical system 2 to the focus accuracy Pb on the detection side before insertion, as follows: The focus accuracy is maintained at the same level.
Pb ′ = 2.0 · Pb (27)

  FIG. 6 is a configuration diagram of an image pickup apparatus including the imaging optical system according to the embodiment. The imaging apparatus includes a camera body C and an imaging optical system L, and the imaging optical system L is mounted on the camera body C in a replaceable manner.

It is the schematic of an imaging optical system. It is explanatory drawing of the ranging frame of a focus detection element. It is explanatory drawing of the ranging frame of a focus detection element. It is explanatory drawing of the ranging frame of a focus detection element. It is a block diagram of the imaging optical system of an Example. It is a block diagram of an imaging device.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Focus movement group 2 Focal length conversion optical system 3 Branch optical system 4a Imaging side partial optical system 4b Detection side partial optical system 5 Imaging means 6 Focus detection element 11 Relay lens group 12 Focus detection means 13 Calculation means 14 Driving means 15 Detection means

Claims (2)

A focus movement group, an optical path branching optical system disposed in an optical path on the image side of the focus movement group, and a focal length conversion optical system disposed detachably between the focus movement group and the optical path branching optical system; A focus detection unit that detects a focused state by the focus movement group using a branched light beam from the optical path branching optical system, a calculation unit that performs an autofocus calculation based on an output of the focus detection unit, and An autofocus imaging optical system having drive control means for driving and controlling the focus movement group based on the output of the calculation means,
A focal length conversion magnification obtained by inserting the focal length conversion optical system into an optical path between the focus moving group and the optical path branching optical system is β2,
The amount of movement of the focus movement group with respect to a predetermined amount of focus change in a state where the focal length conversion optical system is not inserted in the optical path between the focus movement group and the optical path branching optical system is X,
X ′ , a movement amount of the focus movement group with respect to the predetermined amount of focus change in a state where the focal length conversion optical system is inserted in an optical path between the focus movement group and the optical path branching optical system .
The detection-side focusing accuracy in a state where the focal length conversion optical system is not inserted into the optical path between the focus moving group and the optical path branching optical system is Pb,
When the detection-side focusing accuracy in a state where the focal length conversion optical system is inserted in the optical path between the focus moving group and the optical path branching optical system is Pb ′ ,
0.8 <β2 ² · X ′ / X <1.2
0.9 <(Pb ′ · β2) / Pb <1.1
An autofocus imaging optical system characterized by satisfying An imaging apparatus comprising: the autofocus imaging optical system according to claim 1 ; and an imaging unit disposed on an image side of the autofocus imaging optical system.

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