JP4708553B2 - Zoom lens and shooting system - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a zoom lens suitable for a television camera, a video camera, and the like, and in particular, searches for a focal point by wobbling a part of a relay lens group for image formation disposed on the image side of an aperture. The present invention relates to a zoom lens suitable for an autofocus system and having a movable group for flange back adjustment or macro photography.
[0002]
[Prior art]
In recent years, zoom lenses for television cameras are required to have improved operability, ease of use, and mobility as photographers and shooting conditions are diversified. Correspondingly, there is a growing demand for zoom lenses with an autofocus function.
[0003]
In general, in the case of a TV camera etc., it is necessary to secure operability and mobility, so use external measurement type autofocus using infrared light etc. that need to provide a ranging system separately from the imaging system Is not reasonable.
[0004]
Therefore, in a video camera or the like, a method of performing autofocus using a video signal is common. As an autofocus method in a video camera or the like, a method of obtaining a direction discrimination signal for autofocus by driving a part of a lens system or an image sensor with a small amplitude drive (wobbling) in the optical axis direction (so-called hill climbing method). Is effective in improving the accuracy and speed of autofocus.
[0005]
Here, FIG. 14 shows an optical configuration of the zoom lens having the hill-climbing autofocus function.
[0006]
In this figure, I is a first lens group that can move in the optical axis direction for focusing, II is a second lens group that can move in the optical axis direction during zooming, and III is a movement of the imaging position during zooming. Is a third lens group for correcting, IV is a fourth lens group for imaging, Wo is a wobbling lens group, and IG is an imaging surface.
[0007]
In the hill-climbing type, the image position is intentionally changed by wobbling part of the optical system in the optical axis direction, thereby detecting the strength / gradient of the video signal, detecting the best focus direction, and focusing. In this method, focusing is performed by moving the focusing group in a matching direction.
[0008]
For this reason, the optical system to be wobbled needs to have an appropriate sensitivity to back focus.
[0009]
On the other hand, the method of wobbling an image pickup device such as a CCD is advantageous in that a signal can be obtained regardless of the position sensitivity of the movable lens group, but the structure is complicated in that an extra drive means is required, and the cost is low. Disadvantageous.
[0010]
On the other hand, when searching for the focal point by wobbling a part of the optical system for image formation on the image side from the stop, since a relatively small and lightweight lens group is moved, the driving force is small, Since the zooming is performed in a fixed group, the structure is simple and advantageous in terms of cost.
[0011]
However, when a part of the optical system is wobbled in this way, the imaging magnification changes, the imaging position of off-axis light moves, and the image quality deteriorates.
[0012]
For this reason, Japanese Patent No. 2744336 discloses a zoom lens that is compact with a small change in imaging magnification and performs wobbling and focusing using the lens group closest to the image side.
[0013]
[Problems to be solved by the invention]
As described above, in general, in zoom lenses, when wobbling a part of an optical system for image formation on the image side from the stop, features such as quick focusing, reduction in size and weight, and cost reduction are obtained. However, there is a drawback that the image forming magnification is changed with wobbling to deteriorate the image quality. Further, in order to obtain a direction determination signal for autofocus, it is necessary to give the wobbling group an appropriate position sensitivity to back focus.
[0014]
That is, it is necessary to satisfy both an appropriate sensitivity to the back focus of the wobbling group and a small change in imaging magnification accompanying the wobbling.
[0015]
Also, in interchangeable lenses such as TV cameras, a macro shooting mechanism that enables close-up shooting by moving a part of a lens system that is different from the normal focusing lens group, and a lens mount mounting reference surface (flange) ) To the image plane is required to adjust the flange back adjustment mechanism by moving a part of the lens system.
[0016]
Here, when the macro photography or the flange back adjustment mechanism is also performed in a part of the optical system for image formation on the image side from the stop, it is possible to ensure operability and reduce the size and weight. In addition, it is a necessary condition to have an appropriate position sensitivity to the back focus.
[0017]
However, in the above-mentioned Japanese Patent No. 2744336, wobbling and focusing are performed using the lens group closest to the image side, and are fixed during zooming or detection of the best imaging position between the focusing group and the imaging plane. This is not suitable when it is intended to provide a lens group, particularly a movable lens group for flange back adjustment or macro photography.
[0018]
Although it is conceivable to use both a wobbling group and a movable group for performing flange back adjustment, the wobbling driving mechanism and a driving mechanism for performing flange back adjustment and the like are also provided for this combined lens group. If so, there arises a problem that the drive mechanism becomes complicated and the operability such as flange back adjustment deteriorates.
[0019]
Therefore, the present invention has a wobbling group and an adjustment group such as a flange back separately in the optical system on the image side from the stop, and provides the wobbling group with appropriate position sensitivity to the back focus, and at the time of wobbling. It is an object of the present invention to provide a zoom lens with a small change in imaging magnification and a short overall lens length.
[0020]
[Means for Solving the Problems]
In order to achieve the above object, in the present invention, in order from the object side, a first lens group, a second lens group that moves during zooming, and a second lens for correcting the movement of the imaging position during zooming. In a zoom lens having three lens groups and a fourth lens group for image formation and having a stop on the object side of the fourth lens group, the fourth lens group is best in order from the object side. A wobbling group driven by a small amplitude in the optical axis direction to detect the imaging position, and an adjustment including a movable part that is fixed at the time of zooming and detection of the best imaging position and for flange back adjustment or macro photography And a group.
[0021]
In other words, as a fourth lens group for image formation on the object side of the stop, a wobbling group and an adjustment group such as a flange back are separately provided, thereby simplifying a driving mechanism such as a wobbling driving mechanism and a flange back adjustment. It is possible to improve the operability such as flange back adjustment and to make the wobbling group moderately sensitive to back focus and to reduce the change in image magnification during wobbling easily. The zoom lens is realized.
[0022]
Preferably, in the above invention, in the fourth lens group, when the half depth of the back focus change amplitude when the wobbling group is driven in the optical axis direction is defined as the focal depth, the following conditional expression is satisfied: do it.
[0023]
[Expression 4]
[0024]
As a result, it is possible to guarantee the position sensitivity of the wobbling group and adjustment group to an appropriate back focus, and to ensure the necessary back focus as a product. By reducing the level to such a level that there is no wobbling, it is possible to maintain good optical performance with a simple configuration while preventing image degradation during wobbling.
[0025]
Preferably, in the fourth lens group, the following conditional expression is satisfied.
[0026]
[Equation 5]
[0027]
As a result, it is possible to maintain good optical performance with a simple configuration while ensuring the position sensitivity of the wobbling group to an appropriate back focus.
[0028]
Further, the adjustment group is composed of two groups of an object side a group and an image side b group, and the b group is a movable group for flange back adjustment or macro photography. It is preferable to satisfy the formula.
[0029]
[Formula 6]
[0030]
As a result, it is possible to maintain good optical performance with a simple configuration while guaranteeing an appropriate position sensitivity to the back focus of the adjustment group.
[0031]
Then, by specifying the optical constants of each lens group as in the conditional expressions (1) to (4), the movable group for flange back adjustment or macro photography is achieved while reducing the size of the entire lens system. Thus, it is possible to obtain a zoom lens that has good optical performance over the entire zoom range and the entire object distance, and has a small change in imaging magnification during wobbling.
[0032]
The adjustment group may be integrally movable for flange back adjustment or macro photography.
[0033]
Further, a fixed group may be arranged on the object side of the wobbling group in the adjustment group so that the wobbling group can be prevented from being enlarged or aberrations can be corrected satisfactorily.
[0034]
DETAILED DESCRIPTION OF THE INVENTION
1 to 6 show an optical configuration of a zoom lens having an autofocus function according to an embodiment of the present invention. Note that the zoom lens according to the present embodiment is interchangeably attached to a television camera or a video camera (imaging device), and constitutes an imaging system as shown in FIG.
[0035]
In these figures, in order from the object side, I is a first lens group for focusing, II is a second lens group that can be moved during zooming, and III is for correcting the movement of the imaging position during zooming. The third lens group, IV is a fourth lens group for image formation, GB is a glass block such as a color separation prism, and SP is a stop.
[0036]
The first lens group I and the fourth lens group IV are fixed during zooming. The fourth lens group IV is, in order from the object side, a fixed L41 group, a wobbling group L42 group, and is fixed for zooming and detection of the best imaging position, and performs flange back adjustment or macro photography. And an L43 group (adjustment group) including a movable group.
[0037]
In the zoom lenses shown in FIGS. 1 to 4 and 6, the L43 group is composed of an L43a group on the object side and an L43b group on the image side. The L43a group is a fixed group and the L43b group is a flange. It is a movable group for back adjustment or macro photography.
[0038]
In the zoom lens shown in FIG. 5, the entire L43 group is an integrally movable group (L43b group) for flange back adjustment or macro photography.
[0039]
In this zoom lens, the L42 group is wobbled in the optical axis direction, and a direction determination signal for autofocusing is obtained on the image plane. Based on the obtained signal, the focus group is driven to a best focus state.
[0040]
In order to obtain a direction determination signal for autofocus on the image plane, it is necessary to shift the back focus appropriately by wobbling, and the wobbling amount is generally set so that the back focus shifts by about the depth of focus. It is.
[0041]
For example, in a 2/3 type camera (image size: φ11) that is generally used for broadcasting, the allowable circle of confusion is about 0.021 mm, and the depth of focus is about 0.04 mm when the F number is F / 2.0. It becomes. These values differ depending on the image size (1/2 type, 1/3 type).
[0042]
Next, the significance of the conditional expression will be described. First, conditional expression (1) indicates conditions regarding the power of the L42 and L43 groups. By satisfying this conditional expression (1), it is possible to maintain good optical performance with a simple configuration while guaranteeing an appropriate position sensitivity of the L42 group and the L43 group to the flange back.
[0043]
That is, when the power of the L42 group becomes smaller than necessary with respect to the power of the L43 group and exceeds the upper limit of the absolute value of the conditional expression (1), the position sensitivity of the L42 group to the back focus is reduced, and autofocusing is performed. For this reason, a large driving distance is required to obtain a direction discrimination signal.
[0044]
In addition, when the power of the L43 group becomes larger than necessary with respect to the power of the L42 group and exceeds the upper limit of the absolute value of the conditional expression (1), the back focus necessary for the product is secured and the configuration is simple. It becomes difficult to maintain good optical performance.
[0045]
In addition, in this embodiment and the following embodiment, although the case where it has L41 group is shown, L41 group is not necessarily required. However, by providing the L41 group, there is an advantage that the enlargement of the L42 group can be prevented and various aberrations can be corrected satisfactorily.
[0046]
Next, the relationship between the paraxial refractive power arrangement and the image height change (that is, the imaging magnification) due to wobbling will be described with reference to FIG. FIG. 7 is a schematic diagram for explaining an optical action in a lens group for image formation disposed on the image side of the stop. Here, the amount of change Δy in the image height of the central beam on the image plane when one lens group is wobbled will be considered.
[0047]
The stop central principal ray that has passed through the stop SP reaches the image plane IG through the L41, L42, and L43 groups.
[0048]
Here, the incident height to the L41 group is h ₁ (h ₁ = 0 when the L41 group does not exist), the emission angle is α ₄₂ , the power of the L42 group is φ ₄₂ , the power of the L43 group is φ ₄₃ , and the L41 group. The main point interval between the L42 group and the L42 group is e ₁ , the main point interval between the L42 group and the L43 group is e ₂ , and the main point of the L43 group and the imaging plane IG S _k , the image height is y, the wobbling displacement amount of the L42 group is Δx, and the image height change amount during wobbling is Δy, the image height change rate Δy / fw (fw is the focal point at the wide-angle end of the entire system) Distance) is roughly
[0049]
[Expression 7]
[0050]
Have the relationship. Δ represents the difference between the distance a from the principal point position of the L42 group to the virtual image of the stop and the distance b from the principal point position of the L42 group to the virtual image of the imaging position.
[0051]
As described above, moderate focus sensitivity by wobbling requires moderate position sensitivity to the back focus. From conditional expressions (1) and (3), the sensitivity of the back focus Delta] s _k is generally
[0052]
[Equation 8]
[0053]
And
[0054]
Generally the relationship between the displacement amount Δx of sensitivity Delta] s _k and L42 groups back focus,
[0055]
[Equation 9]
[0056]
Therefore, the image height change rate Δy / fw when the L42 group having moderate back focus sensitivity is displaced is approximately:
[0057]
[Expression 10]
[0058]
It can be expressed by the relationship.
[0059]
Here, it is said that the resolution of human vision with a visual acuity of 1.0 is about 1 minute. For example, when a human views a television screen of 30 inches (horizontal screen size is about 50 cm) from a position 2.5 m away, the horizontal viewing angle is about 680 minutes. Accordingly, the resolution of about 1 minute corresponds to 0.15% on the screen.
[0060]
When the aperture is reduced, the depth of focus becomes deeper than when the aperture is opened, and the amount of wobbling necessary to detect the best focus position also increases, so the rate of change in image height also increases. Accordingly, since the F-number area with the highest frequency of use is about open to F / 5.6, if the image height change rate at F / 5.6 is allowed to 0.15%, the F number area is open (F / 1.85). ) Is about 0.06% of about 1/3. Therefore, the upper limit of conditional expression (2) is such that the image height change rate when the aperture is open (F / 1.85) is within 0.06% (0.15% when F / 5.6). Were determined.
[0061]
However, when considering a system that frequently uses an F-number of F / 5.6 or higher, or when a brighter open F-number is set, the image height change rate at the time of opening should be kept below 0.06%. Is required.
[0062]
The upper limit value of the allowable image height change rate indicated by the conditional expression (2) varies depending on the concept of determining the wobbling amount with respect to the focal depth, the assumed screen size, and the like, but the range of the conditional expression (2) As shown in Table 7 to be described later, it falls within 0.06%.
[0063]
Conditional expression (3) relates to the power at the wide-angle end of the L42 group and the entire system, and shows conditions for guaranteeing appropriate position sensitivity to back focus and maintaining good optical performance. Is.
[0064]
When the power of the L42 group becomes smaller than the power at the wide-angle end of the entire system and falls below the lower limit of the conditional expression (3), the position sensitivity to the back focus decreases, and a direction determination signal for autofocus is generated. In order to obtain this, the amount of movement of the wobbling group must be increased, and the distance between the movable parts is required to be wide, which is contrary to downsizing.
[0065]
Further, when the power of the L42 group becomes large and exceeds the upper limit of the conditional expression (3), the position sensitivity to the back focus increases, and the displacement amount of the L42 group mechanically with respect to the determined back focus displacement amount. It becomes difficult to control. In addition, it becomes difficult to maintain good optical performance with a simple configuration.
[0066]
Conditional expression (4) divides the L43 group into two groups, that is, the L43a group on the object side and the L43b group on the image side, and limits the power of each lens group. This is for setting as a movable lens group for flange back adjustment and macro photography with position sensitivity to the lens.
[0067]
When the power of the L43a group becomes larger than necessary with respect to the power of the L43b group or when the power of the L43b group becomes smaller than necessary with respect to the power of the L43a group, the upper limit of the conditional expression (4) is exceeded. There are disadvantages in that the lens configuration for maintaining good optical performance is complicated, the position sensitivity of the L43 group with respect to the back focus is reduced, and a large interval between movable parts is required.
[0068]
As described above, when the optical constants of the respective lens groups satisfy the conditional expressions (1) to (4), the zoom lens system as a whole can be made compact and movable for flange back adjustment or macro photography. Secure the L43 group separately from the L42 group, which is the wobbling group, to achieve good optical performance over the entire zoom range and the entire object distance, and realize a zoom lens with small change in imaging magnification during wobbling is doing.
[0069]
Tables 1 to 6 below show numerical examples of the zoom lens shown in FIGS. FIGS. 8 to 13 show various aberration diagrams at the wide-angle end (A) and the telephoto end (B) in the numerical examples.
[0070]
In Table 1, Numerical Example 1 and various aberration diagrams in FIG. 8 are shown in the zoom lens in FIG. 1, Numerical Example 2 in Table 2 and various aberration diagrams in FIG. 9 are in the zoom lens in FIG. The aberration diagrams of Example 3 and FIG. 10 are for the zoom lens of FIG. 3, the numerical example 4 of Table 4 and the aberrations of FIG. 11 are for the zoom lens of FIG. 4, and the numerical examples 5 and 12 of Table 5. The aberration diagrams in FIG. 5 correspond to the zoom lens in FIG. 5, and the aberration diagrams in Numerical Example 6 and FIG. 13 in Table 6 correspond to the zoom lens in FIG. 6.
[0071]
[Table 1]
(Numerical example 1)
[0072]
[Table 2]
(Numerical example 2)
[0073]
[Table 3]
(Numerical Example 3)
[0074]
[Table 4]
(Numerical example 4)
[0075]
[Table 5]
(Numerical example 5)
[0076]
[Table 6]
(Numerical example 6)
[0077]
As can be seen from the above numerical examples, according to the present embodiment, the zoom lens has an autofocus function with an F number of about F / 2.0, a large aperture ratio of 10 times or more, and a high magnification ratio. Can be realized.
[0078]
Next, Table 7 summarizes the relationship between each numerical example and the conditional expressions (1) to (4).
[0079]
Here, in the numerical examples 1 to 2 phi ₄₂ positive, phi ₄₂ in Numerical Example 3-6 is negative. In Numerical Example 5, the L43 group can be moved together for flange back adjustment or macro photography. Further, in Numerical Example 6, both the L43a group and the L43b group have positive power.
[0080]
[Table 7]
[0081]
Thus, according to the present embodiment, as the fourth lens group for imaging on the object side of the stop SP, the L42 group that is a wobbling group and the L43 group that is an adjustment group such as a flange back are separately provided. Since it is provided, the driving mechanism such as the wobbling driving mechanism and the flange back adjustment can be simplified, the operability such as the flange back adjustment can be improved, and the L42 group can have an appropriate position sensitivity to the back focus. Therefore, it is possible to realize a zoom lens that can easily achieve both the reduction of the change in the imaging magnification during wobbling.
[0082]
Next, an embodiment of a photographing system (TV camera system) using the zoom lenses of Numerical Examples 1 to 6 as a photographing optical system will be described with reference to FIG.
[0083]
In FIG. 15, reference numeral 106 denotes a photographing system main body including a lens, 101 denotes a photographing optical system constituted by the zoom lenses of Numerical Examples 1 to 6, 102 denotes a glass block corresponding to a filter or a color separation prism, and 103 denotes a photographing optical system. An image sensor such as a CCD that receives a subject image formed by the camera 101, and CPUs 104 and 105 that control the photographing apparatus and the lens.
[0084]
Thus, by applying the zoom lenses of Numerical Examples 1 to 6 to a photographing system such as a TV camera, the wobbling driving mechanism and the driving mechanism such as the flange back adjustment are simplified, and the operability such as the flange back adjustment is improved. At the same time, it is possible to realize an imaging system in which it is easy to make the wobbling group have an appropriate position sensitivity to the back focus and maintain good optical performance.
[0085]
【The invention's effect】
As described above, according to the present invention, the wobbling group and the adjustment group for flange back adjustment or macro photography are separately provided as the fourth lens group for imaging on the object side of the stop. Therefore, the driving mechanism such as the wobbling driving mechanism and the flange back adjustment can be simplified, and the operability such as the flange back adjustment can be improved. Furthermore, it is possible to realize a zoom lens in which it is easy to make both the wobbling group have an appropriate position sensitivity to the back focus and to reduce the change in imaging magnification during wobbling.
[0086]
In particular, in the fourth lens group, the conditional expressions (1) and (2) are satisfied when the half depth of the back focus change amplitude when the wobbling group is driven in the optical axis direction is the focal depth. This ensures the position sensitivity of the wobbling group and adjustment group to an appropriate back focus, ensuring the necessary back focus as a product, and practically changing the image magnification due to wobbling. By reducing it to a level where there is no problem, it is possible to maintain good optical performance with a simple configuration while preventing image degradation during wobbling.
[0087]
Further, in the fourth lens group, if conditional expression (3) is satisfied, good optical performance can be maintained with a simple configuration while guaranteeing an appropriate position sensitivity to the back focus of the wobbling group. It becomes possible.
[0088]
Further, the adjustment group is composed of two groups of an object side a group and an image side b group. The b group is a movable group for flange back adjustment and macro photography. If 4) is satisfied, it is possible to maintain good optical performance with a simple configuration while guaranteeing an appropriate position sensitivity to the back focus of the adjustment group.
Good optical performance can be maintained.
[0089]
Then, by specifying the optical constants of each lens group as in the conditional expressions (1) to (4), the movable group for flange back adjustment or macro photography is achieved while reducing the size of the entire lens system. It is possible to obtain a zoom lens that has good optical performance over the entire zooming range and the entire object distance, and has a small change in imaging magnification during wobbling.
[0090]
Note that if the fixed group is disposed on the object side of the wobbling group in the adjustment group, it is possible to suppress an increase in the size of the wobbling group or correct aberrations favorably.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating an optical configuration of a zoom lens according to an embodiment (Numerical Example 1) of the present invention.
FIG. 2 is a diagram illustrating an optical configuration of a zoom lens according to an embodiment (Numerical Example 2) of the present invention.
FIG. 3 is a diagram illustrating an optical configuration of a zoom lens according to an embodiment (Numerical Example 3) of the present invention.
FIG. 4 is a diagram illustrating an optical configuration of a zoom lens according to an embodiment (Numerical Example 4) of the present invention.
FIG. 5 is a diagram illustrating an optical configuration of a zoom lens according to an embodiment (Numerical Example 5) of the present invention.
FIG. 6 is a diagram illustrating an optical configuration of a zoom lens according to an embodiment (Numerical Example 6) of the present invention.
FIG. 7 is an explanatory diagram of an optical action of a fourth lens group for image formation in the zoom lens.
FIG. 8 is a diagram illustrating various aberrations of the zoom lens according to Numerical Example 1;
FIG. 9 is a diagram illustrating various aberrations of the zoom lens according to Numerical Example 2.
FIG. 10 is a diagram illustrating all aberrations of the zoom lens according to Numerical Example 3;
FIG. 11 is a diagram illustrating all aberrations of the zoom lens according to Numerical Example 4;
12 is a diagram illustrating all aberrations of the zoom lens according to Numerical Example 5. FIG.
FIG. 13 is a diagram illustrating all aberrations of the zoom lens according to Numerical Example 6;
FIG. 14 is a diagram illustrating an optical configuration of a zoom lens having a so-called hill-climbing autofocus function.
FIG. 15 is a schematic diagram of a photographing system using the zoom lenses of Numerical Examples 1 to 6 as a photographing optical system.
[Explanation of symbols]
I First lens group
II Second lens group
III Third lens group
IV Fourth lens group SP Aperture L41 Fixed group L42 Wobbling group L43 Adjustment group L43a Fixed group L43b Movable group IG Imaging surface

Claims (6)

In order from the object side, the first lens group, the second lens group that moves during zooming, the third lens group for correcting the movement of the imaging position during zooming, and the fourth lens for imaging A zoom lens having a stop on the object side of the fourth lens group,
The fourth lens group includes, in order from the object side, a wobbling group that is driven with a small amplitude in the optical axis direction in order to detect the best imaging position, and a flange that is fixed at the time of zooming and detection of the best imaging position. And an adjustment group including a movable part for back adjustment or macro photography, and the half depth of the back focus change amplitude when the wobbling group is driven in the optical axis direction is defined as the depth of focus. In some cases, the zoom lens satisfies the following conditional expression:
The zoom lens according to claim 1, wherein the fourth lens group satisfies the following conditional expression.
The adjustment group is composed of two groups, an a-group on the object side and a b-group on the image side. The b-group is a movable group for flange back adjustment and macro photography, and satisfies the following conditional expression: The zoom lens according to claim 1 or 2 , characterized in that:
The zoom lens according to claim 1 or 2, characterized in that the movable said adjustment group together for flange back adjustment, or macro photography. Wherein the object side than the wobbling unit zoom lens according to any one of claims 1 to 4, characterized in that a fixed group. Imaging system to claim 1 and the zoom lens according to any one of 5, characterized in that the zoom lens is configured to have an imaging device which is exchangeably mounted.