JP2005140969A - Zoom lens and imaging apparatus having the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a compact zoom lens having not only a focusing moving group arranged nearer to an image side than a variable power moving group but also a focusing moving group nearer to an object side than the variable power moving group, performing focusing by both of them and having high optical performance, and to provide an imaging apparatus having the zoom lens. <P>SOLUTION: The zoom lens has a 1st lens group having positive refractive power, a 2nd lens group having negative refractive power, a 3rd lens group having positive or negative refractive power, and a 4th lens group having positive refractive power in order from an object side to an image side, and the 2nd lens group and the 3rd lens group are moved in the case of zooming. The 4th lens group has a 4a lens group, a 4b lens group and a 4c lens group in order from the object side to the image side, and performs focusing by moving the 4b lens group on an optical axis, and it is constituted to satisfy ¾β4c¾>1 when it is assumed that the image forming magnification of the 4c lens group is β4c. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a zoom lens and an image pickup apparatus having the same, and is suitably used for electronic cameras such as video cameras and digital still cameras, film cameras, broadcast cameras, and the like.

  Various proposals have been made for so-called rear focus systems that focus on zoom lenses used in film cameras and video cameras by moving the rear lens group (image side) from the variable power lens group. (For example, Patent Documents 1 to 4).

  In the rear focus method, a relatively small and light lens group is moved during focusing, so that a driving force is small and quick focusing can be performed.

  For this reason, a rear focus type zoom lens in which a focusing movement group (focus lens group) as a focusing lens group is arranged closer to the image side than a zooming movement group as a variable magnification lens group is an autofocus type zoom lens. Many have been adopted.

  On the other hand, the front-lens focus type zoom lens that places the focusing movement group closer to the object side than the zooming movement group does not change even if zooming is performed, as long as the amount of extension of the focusing movement group is constant, the manual distance This is advantageous for the focus method (manual method). For this reason, it is widely used in broadcast zoom lenses and professional zoom lenses that place emphasis on manual operation.

In view of these points, zoom lenses that use an image-side lens group from the zooming group during autofocus and a lens group that uses the object side lens from the zooming group during manual focus are known. (For example, Patent Documents 5 and 6).
Japanese Patent Application No. 2001-21803 Japanese Patent Application No. 2001-343583 JP-A-11-305124 JP 2001-194586 A Japanese Patent No. 261637 Japanese Utility Model Publication No. 62-043286

  At the zoom position of the focal length f of the zoom lens, the image point when the object distance is changed when the image point at the object distance infinity is i0 and the image point with respect to the object distance obj is i (obj) The amount of change Δsk = i (obj) −i0 is expressed by the following equation from Newton's formula.

Δsk = f ² / (obj−f) (1)
Therefore, when the focusing operation is performed in the sub-system B1 closer to the object side than the zooming movement group, the change amount ΔskB1 of the imaging point at the object distance obj is
ΔskB1 = fB1 ² / (obj−fB1) (2)
And is constant regardless of the zoom position (magnification). Accordingly, the feed amount ΔxFF for focusing of the partial system (focusing lens group) FF in the partial system B1 does not change regardless of the zoom state.

  However, when focusing is performed with the lens group on the image side of the zooming movement group, the shift ΔskB1 of the imaging point in the sub-system B1 is enlarged or reduced in the sub-system B2 that is the zooming movement group, and is roughly expressed by the following equation. Is done.

ΔskB2 = {fB1 ² / (obj−fB1)} βB2 ² (3)
Accordingly, when focusing is performed with the partial system FR in the partial system B3 which is the lens group on the image side of the variable magnification moving group, the feed amount ΔxFR of the partial system FR is proportional to the square of the imaging magnification βB2 of the variable magnification moving group. Increase. Therefore, as the zoom ratio increases, the amount of feeding of the partial system FR during focusing increases, the movement space of the partial system FR increases, and the driving force for moving the partial system FR by a required amount increases. The whole becomes bigger.

  Prior Patent Document 5 is a four-group zoom lens composed of lens groups having positive, negative, positive, and positive refractive power in order from the object side to the image side, and the fourth lens group is moved with a compensator (variable magnification). Since the image plane is corrected) and the focusing action are combined, there is a problem that manual zooming operation cannot be performed.

  Patent Document 6 is a four-group zoom lens composed of lens groups having positive, negative, negative, and positive refractive powers in order from the object side to the image side. The first lens group is used for manual focusing, and the second lens group is a variator ( The zoom lens group), the third lens group is a compensator (image point movement correction group), and the rear lens group of the fourth lens group is a focusing lens group for autofocus.

  In Patent Document 6, the zoom ratio is as low as 6 times or less, and the focal length at the zoom position at the telephoto end is also relatively short, around 70 mm. For this reason, if the zoom ratio is further increased and the focal length at the telephoto end is increased, the amount of extension at the time of focusing of the rear lens group of the fourth lens group is rapidly increased, and the entire lens system is enlarged. There was a point.

  The present invention provides a zoom lens and an image pickup apparatus having the same, which have a high zoom ratio, reduce the maximum amount of movement of the focusing lens group, reduce the size of the entire lens system, and have high optical performance over the entire object distance. For the purpose of provision.

The zoom lens according to the first aspect of the invention includes, in order from the object side to the image side, a first lens group having a positive refractive power, a second lens group having a negative refractive power, a third lens group having a positive or negative refractive power, In a zoom lens having a fourth lens unit having a positive refractive power and moving the second lens unit and the third lens unit during zooming, the fourth lens unit is arranged in order from the object side to the image side. When there is a 4a lens group, a 4b lens group, and a 4c lens group, the 4b lens group moves on the optical axis to perform focusing, and the imaging magnification of the 4c lens group is β4c ,
| Β4c |> 1
It is characterized by satisfying.

  According to the zoom lens of the present invention, although the zoom ratio is high, the maximum moving amount of the focusing lens group is reduced, the entire lens system is downsized, and high optical performance can be obtained over the entire object distance.

  In addition, the present invention employs a rear focus system having a focusing movement group on the image side of the zooming movement group, and the absolute value of the imaging magnification or conversion magnification exceeds 1 on the image side of the focusing movement group. By disposing a fixed lens group, the maximum extension amount during focusing of the in-focus movement group can be reduced, and the entire lens system can be easily downsized while maintaining a high zoom ratio.

  Embodiments of the zoom lens of the present invention and an image pickup apparatus having the same will be described below.

  FIG. 1 is a lens cross-sectional view at the wide-angle end of a zoom lens according to Embodiment 1 of the present invention.

  In the following aberration diagrams, FIGS. 2 to 6, FIGS. 8 to 12, and each example, a value when a numerical example described later is expressed in mm is used as a reference. f is a focal length. The object distance is the distance measured from the image plane.

FIG. 2 is an aberration diagram of Example 1 at f = 10.30 mm and an object distance of 3 m.
FIG. 3 is an aberration diagram of Example 1 at f = 39.45 mm and an object distance of 2.5 m.
FIG. 4 is an aberration diagram of Example 1 at f = 151.10 mm and an object distance of 2.5 m.
FIG. 5 is an aberration diagram of Example 1 at f = 151.10 mm, at an object distance of infinity.
FIG. 6 is an aberration diagram of Example 1 at f = 151.10 mm and an object distance of 1 m.

FIG. 7 is a lens cross-sectional view at the wide-angle end of the zoom lens according to Example 2 of the present invention;
FIG. 8 is an aberration diagram of Example 2 at f = 11.30 mm and an object distance of 5 m.
FIG. 9 is an aberration diagram of Example 2 at f = 43.84 mm and an object distance of 5 m.
FIG. 10 is an aberration diagram of Example 2 at f = 169.52 mm and an object distance of 5 m.
FIG. 11 is an aberration diagram of Example 2 at f = 169.52 mm, at an object distance of infinity.
FIG. 12 is an aberration diagram for Example 2 at f = 169.52 mm and an object distance of 1 m.

13 and 14 are explanatory diagrams of the paraxial refractive power arrangement of the zoom lens of the present invention.
FIG. 13 is a conceptual diagram when the third lens group has a negative refractive power,
FIG. 14 is a conceptual diagram when the third lens unit has a positive refractive power.

  FIG. 15 is a schematic view of a main part of a video camera (imaging device) including the zoom lens according to the present invention.

  FIG. 16 is a schematic diagram of a main part of a digital camera (imaging device) including the zoom lens of the present invention.

  The zoom lens of each embodiment is a photographing lens system used in an imaging apparatus. In the lens cross-sectional view, the left side is the subject side (front) and the right side is the image side (rear).

  The zoom lens according to the embodiment of the present invention includes, in order from the object side to the image side, a first lens unit L1 having a positive refractive power, a second lens unit L2 having a negative refractive power, and a third lens having a positive or negative refractive power. The lens unit L3 includes a fourth lens unit L4 having a positive refractive power, and the second lens unit L2 and the third lens unit L3 move during zooming.

The fourth lens unit L4 includes, in order from the object side to the image side, a fourth lens unit L4a having a positive refractive power, a fourth lens unit L4b having a positive refractive power, and a fourth lens unit L4c having a negative refractive power. When the 4b lens unit L4b moves on the optical axis to perform focusing, and the imaging magnification of the 4c lens unit L4c is β4c,
| Β4c |> 1 (4)
Is satisfied.

In this embodiment, by defining the minimum value of the imaging magnification β4c of the fourth c lens unit L4c as in the conditional expression (4), the maximum amount of extension of the fourth b lens unit L4b is reduced, and the fourth lens unit L4 is reduced in size. It has become. From the equation (2), the maximum value Δskmax of the change amount of the image forming point accompanying the change in the object distance is expressed by fT as the focal length at the telephoto end of the zoom lens and MOD as the close distance.
Δskmax = fT ² / (MOD−fT) (8)
It can be expressed as Assuming that the imaging magnifications of the fourth b lens group L4b and the fourth c lens group L4c are β4b and β4c, respectively, the sensitivity dsk4b of the displacement of the imaging point accompanying the movement of the fourth b lens group L4b during focusing is
dsk4b = (1-β4b ² ) β4c ² (9)
It is represented by Since the maximum extension amount Δxmax of the fourth lens group L4b is proportional to Δskmax, 1 / dsk4b,
Δxmax ∝ fT ² / {(MOD−fT) · (1-β4b ² ) β4c ² }
(10)
There is a relationship. Since Δxmax is proportional to 1 / β4c ² from equation (10), by setting | β4c |> 1, the maximum extension amount Δxmax is reduced, the moving space is reduced, and the fourth lens unit L4 is reduced in size. I am trying.

  During zooming from the wide-angle side to the telephoto side, the second lens unit L2 moves on the optical axis from the object side to the image side. When the third lens unit L3 has a negative refractive power as shown in the conceptual diagrams, FIGS. 13 and 14, the third lens unit L3 moves to the image side after moving to the object side on the optical axis.

  When the third lens unit L3 has a positive refractive power, the third lens unit L3 moves on the optical axis from the image side to the object side, and passes through a zoom position where the imaging magnification is -1 times. .

  13 and 14, W and T indicate zoom positions at the wide-angle end and the telephoto end, respectively, ∞ indicates an object at infinity, and MOD indicates a close object.

  Further, a rear focus type is employed in which focusing is performed by moving the fourth lens group L4b on the optical axis. A line 4b1 and a curve 4b2 relating to the fourth lens unit L4b are movement trajectories for correcting image plane fluctuations caused by zooming when focusing on an object at infinity and an object at close distance, respectively.

  In each embodiment, for example, when focusing from an infinitely distant object to a close object at the telephoto end, the fourth lens group L4b is extended forward as indicated by an arrow 4b3.

  By defining the second lens group L2 as a zooming movement group and the third lens group L3 as an image point movement correction group accompanying zooming, it is specified that the focusing movement group is independent of the image point movement correction group. Thus, the second lens group L2 and the third lens group L3 can be moved independently of the in-focus movement group by means such as a mechanical cam, so that manual zooming operation is possible.

When the imaging magnification of the 4b lens unit L4b is β4b,
| (1-β4b ² ) · β4c ² |> 1 (5)
Is satisfied.

Or -0.3 <β4b <0.3 (a)
Is satisfied.

More preferably,
−0.2 <β4b <0.2
It is good to do.

The imaging magnification at an arbitrary zoom position in the entire system is β, the imaging magnification of the first lens unit L1 is β1, and the imaging magnification β in a state where focusing by the 4b lens unit L4b is not performed is β = 0 and β1 The position on the optical axis of the first lens unit L1 where = 0 is the reference position x0, the imaging magnification by the lens unit after the second lens unit L2 is β ₂₃₄ , the F number of the entire system is F, and the minimum circle of confusion diameter is When δ, the position x on the optical axis of the first lens unit L1 is
| (X−x0) · (β ₂₃₄ ) ² / (δF) | <1 (6)
When the above condition is satisfied, focusing by the fourth lens group L4b is performed.

  The maximum value of the imaging magnification of the 4b lens group is defined as in the conditional expression (5), the maximum extension amount Δxmax of the 4b lens group L4b is made smaller, and the fourth lens group L4 is made more compact. .

  In this embodiment, auto focus is performed by the 4b lens unit L4b, and all or part of the first lens unit L1 is used as a manual focus lens unit.

  In this way, the focusing operation can be performed by moving the entire first lens group L1 or a part of the first lens group L1 on the optical axis as a manual focus group, thereby achieving both manual focus and autofocus.

  By making the whole or a part of the fourth lens unit L4 movable on the optical axis, a flange back adjustment mechanism that is indispensable for a zoom lens of an interchangeable lens manual focus type is realized.

  Only when the first lens unit L1 that is the manual focus unit is in focus on an object at infinity, the focusing operation is performed with the 4b lens unit that is the autofocus unit.

The depth of focus D when the minimum circle of confusion of the imaging system is δ and the F number is F is
D = δF (11)
It is represented by The imaging position shift amount Δsk due to the extension of the first lens unit L1 is x, where the principal point position of the first lens unit L1 is x, the principal point position of the first lens unit L1 during infinite focus is x0, When the imaging magnification after the second lens group is β ₂₃₄ ,
Δsk = (x−x0) · (β ₂₃₄ ) ² ... (12)
It is represented by Therefore, if the condition of the expression (4) is satisfied, the first lens unit L1 can be regarded as being focused on an object at infinity within the focal depth.

In Example 1 of FIG. 1, an image size conversion optical system sh that can be inserted and removed is provided on the object side of the fourth lens group L4b in the fourth lens group L4, and the conversion magnification is βsh.
βsh <1
Is satisfied.

At this time, the maximum extension amount of the 4b lens unit L4b during insertion into the optical path of the image size conversion optical system sh is shmax, and the 4b lens unit L4b before insertion into the optical path of the image size conversion optical system sh When the maximum feed amount is smax,
0.9 <shmax / (βsh ² · smax) <1.1 (7)
Is satisfied.

  This effectively converts the focal length range.

  Then, the maximum feed amount Δshmax when the image size conversion optical system sh is inserted satisfies the expression (7) so that the object at close range is almost unchanged before and after the image size conversion optical system sh is inserted. . It can be demonstrated that there is no sense of incongruity if the difference in the feed amount is within 10%.

  In FIG. 1, L1 is a positive refractive power focus group (front lens group) as the first lens group. L2 is a variable power negative variator (magnification moving group) as a second lens group, and is moved from the wide angle end (wide) by monotonously moving on the optical axis to the image plane side. It is zooming to the telephoto end (tele). L3 is a negative refractive power compensator (image point movement correction group) serving as a third lens group, and has a locus convex toward the object side on the optical axis in order to correct image plane variation accompanying zooming. Have non-linear movement. The variator 2 and the compensator 3 constitute a variable power system.

  SP is a stop, and L4 is a fixed relay group for zooming with a positive refractive power as the fourth lens group, and has three lens groups L4a, L4b, and L4c. P is a color separation prism, an optical filter, or the like, and is shown as a glass block in FIG.

  IP is an image plane, and when used as a photographing optical system for a video camera or a digital still camera, the imaging surface of a solid-state imaging device (photoelectric conversion device) such as a CCD sensor or a CMOS sensor is a camera for a silver telephoto film. Corresponds to the film surface.

  In the aberration diagrams, d and g are d-line and g-line, respectively, ΔM and ΔS are meridional image plane, sagittal image plane, and lateral chromatic aberration are represented by g-line.

  Next, features of the fourth lens unit L4 in Embodiment 1 will be described. The fourth lens unit L4 has a positive refractive power as a whole. In order from the object side to the image side, the fourth lens unit L4a having a positive refractive power, the fourth lens unit L4b having a positive refractive power, and a negative power unit. The fourth lens unit L4c has a refractive power. Here, the 4b lens group is a (focusing movement group) as a focus lens group, and moves on the optical axis to the object side when focusing from a long distance object to a short distance object.

  During autofocusing (automatic focusing operation), a known autofocusing mechanism is used to drive the 4b lens group L4b with driving means (not shown).

In this embodiment, when the closest object (closest object distance that can be photographed) is 1 m, the maximum amount of extension Δxmax when focusing from the infinite object to the close object in the 4b lens group is The amount of movement is positive and is -12.4 mm. The value on the right side of equation (10) is
(Right side of equation (10)) = 151.1 ² /{(−1000-151.1)·(1−0.1788 ² ) · 1.1014 ² } = − 16.9
It becomes. Since the maximum feed amount Δxmax is proportional to 1 / β4c ² , in this embodiment, by setting β4c = 1.1, the maximum feed amount Δxmax is reduced by about 18%, the moving space is reduced, and the fourth lens is reduced. The size of the group L4 is reduced.

  In this embodiment, the second lens unit L2 is a variable power moving unit with negative refractive power, the third lens unit L3 is an image point moving correction unit with negative refractive power, and the in-focus moving unit L4b is image point moving corrected. It is independent of the group L3. The second lens group L2 and the third lens group L3 can be moved independently of the focusing movement group L4b by means such as a mechanical cam, so that manual zooming operation is possible.

  Note that the imaging magnification β4b of the fourth lens group L4b in the present embodiment is 0.179, which satisfies the expression (a).

  In this embodiment, the entire first lens group L1 or a part of the first lens group L1 is moved on the optical axis as a manual focus group so that a focusing operation can be performed, thereby achieving both manual focus and autofocus. Further, by making the whole or part of the fourth lens unit L4 movable on the optical axis, a flange back adjustment mechanism that is indispensable for a zoom lens of an interchangeable lens manual focus system is realized.

  Furthermore, in this embodiment, the fourth lens unit L4b, which is an autofocus group, performs a focusing operation only when the first lens unit L1, which is a manual focus group, is in focus on an object at infinity.

With respect to the F number Fno at the wide-angle end and the telephoto end of the zoom lens of the present embodiment, the focal depth D, the imaging magnification β ₂₃₄ by the lens units after the second lens unit L2, and the reference position xo of the first lens unit L1 when the aperture is opened. Table 1 shows the difference | x−x0 | from the position x of the first lens unit L1. Note that the minimum circle of confusion δ is 0.021 mm assuming an NTSC, 2/3 type imaging system.

From Table 1, when the aperture is open, | x−x0 | <2.377 mm at the wide-angle end, and Equation (6) becomes 0.9988, and at the telephoto end, | x−x0 | <0.0125 mm, and Equation (6) becomes 0 .9989, and when the condition of the expression (6) is satisfied, focusing by the fourth lens group L4b is performed.

  In the present embodiment, an image size conversion optical system sh that can be inserted and removed has a conversion magnification βsh = 0.83 times on the object side of the 4b lens group. The focal length of the entire system when the image size conversion optical system sh is inserted into the optical path is 0.83 times, and the maximum extension amount Δshmax at the time of focusing of the 4b lens group when the closest object is 1 m is -8.3 mm, 0.67 times before the image size conversion optical system sh is inserted, and the relationship of the expression (10) is satisfied. Therefore, when the expression (5) is satisfied, an object at a close distance before and after the image size conversion optical system sh is inserted into the optical path is almost unchanged. It can be demonstrated that there is no sense of incongruity if the difference in the feed amount is within 10%.

In FIG. 7, L1 is a positive refractive power focus group (front lens group) as the first lens unit L1. L2 is a variator having a negative refractive power for zooming as the second lens unit, and is moved monotonously on the optical axis from the wide-angle end (wide) to the telephoto end (tele). The zooming is done. L3 is a compensator having a positive refractive power, and moves monotonously and non-linearly on the optical axis to the object side in order to correct image plane fluctuations accompanying zooming. The variator L2 and the compensator L3 constitute a variable power system.

  SP is a stop, and L4 is a fixed relay group for zooming with a positive refractive power as the fourth lens group, and has three lens groups L4a, L4b, and L4c. P is a color separation prism, an optical filter, or the like, and is shown as a glass block in FIG.

  Next, features of the fourth lens unit L4 in Embodiment 2 will be described. The fourth lens unit L4 has a positive refracting power as a whole, and in order from the object side to the image side, the fourth a lens unit L4a having a negative refracting power, the fourth b lens unit L4b having a positive refracting power, The fourth lens unit L4c has a refractive power. Here, the 4b lens group L4b is a focus group (focus movement group), and moves on the optical axis to the object side when focusing from an object at infinity to an object at a short distance.

In this embodiment, when the object at close distance is 1 m, the maximum extension amount Δxmax at the time of focusing from the object at infinity to the object at close distance in the 4b lens unit L4b is set to −13. 1 mm. The value on the right side of equation (10) is
(Right side of equation (10)) = 169.52 ² /{(−1000−169.52)·(1−0.0707 ² ) · 1.103 ² }
= -20.3
It becomes. Since the maximum feed amount Δxmax is proportional to 1 / β4c ² , in this embodiment, by setting β4c = 1.1, the maximum feed amount Δxmax is reduced by about 18%, the moving space is reduced, and the fourth lens is reduced. The size of the group L4 is reduced.

  In this embodiment, the second lens unit L2 is a variable power moving unit with negative refractive power, the third lens unit L3 is an image point moving correction unit with positive refractive power, and the in-focus moving unit L4b is image point moving corrected. It is independent of the group L3. The second lens group L2 and the third lens group L3 can be moved independently of the focusing movement group L4b by means such as a mechanical cam, so that manual zooming operation is possible.

  The imaging magnification β4b of the 4b lens unit L4b in the present embodiment is 0.0707, which satisfies the expression (a).

  In this embodiment, the entire first lens group L1 or a part of the first lens group L1 is moved on the optical axis as a manual focus group so that a focusing operation can be performed, thereby achieving both manual focus and autofocus. Further, by making the whole or part of the fourth lens unit L4 movable on the optical axis, a flange back adjustment mechanism that is indispensable for a zoom lens of an interchangeable lens manual focus system is realized.

  Furthermore, in this embodiment, the 4b lens group which is an autofocus group performs a focusing operation only when the first lens group L1 which is a manual focus group is in focus on an object at infinity.

The values of the F number Fno at the wide-angle end and the telephoto end of the zoom lens of the present embodiment, the focal depth D, the imaging magnification β ₂₃₄ by the lens units after the second lens unit L2, and the difference | x−x0 | It is shown in 2. Note that the minimum circle of confusion δ is 0.021 mm assuming an NTSC, 2/3 type imaging system.

From Table 2, when the aperture is open, | x−x0 | <4.641 mm at the wide-angle end, and Equation (6) is 1.000. Also, at the telephoto end, | x−x0 | <0.035 mm, and the expression (6) becomes 0.9913, which satisfies the condition of the expression (6) and performs focusing by the 4b group.

  In the following, numerical examples 1 and 2 respectively corresponding to the examples 1 and 2 will be shown. In each numerical example, i indicates the order of the surfaces from the object side, ri is the radius of curvature of each surface, di is the member thickness or air spacing between the i-th surface and the (i + 1) -th surface, and ni and νi are The refractive index and Abbe number for d line are shown. In Numerical Examples 1 and 2, the three surfaces closest to the elephant side and in Numerical Example 2 the two surfaces closest to the image side are planes corresponding to glass blocks.

  f represents a focal length, Fno represents an F number, and ω represents a half angle of view. Table 1 shows the relationship between the above-described conditional expressions and numerical values in the numerical examples.

  Next, embodiments of a video camera and a digital camera using the zoom lens of the present invention as a photographing optical system will be described with reference to FIGS.

  In FIG. 15, 10 is a video camera body, 11 is a photographing optical system constituted by the zoom lens of the present invention, 12 is a solid-state image pickup device (photoelectric conversion) such as a CCD sensor or a CMOS sensor that receives a subject image by the photographing optical system 11. (Element), 13 is a memory for storing information corresponding to the subject image photoelectrically converted by the image sensor 12, and 14 is a finder for observing the subject image displayed on a display element (not shown). The display element is constituted by a liquid crystal panel or the like, and a subject image formed on the image sensor 12 is displayed.

  In FIG. 16, 20 is a camera body, 21 is a photographing optical system constituted by the zoom lens of the present invention, 22 is a CCD sensor or CMOS sensor built in the camera body, and receives a subject image formed by the photographing optical system 21. A solid-state image sensor (optical conversion element) such as 23, a memory 23 for recording information corresponding to the subject image photoelectrically converted by the solid-state image sensor 22, and a liquid crystal display panel 24 are formed on the solid-state image sensor 22. It is a finder for observing the subject image.

  Thus, by applying the zoom lens of the present invention to an imaging apparatus such as a video camera, an imaging apparatus having a small size and high optical performance can be realized.

Lens cross-sectional view at the wide-angle end of the zoom lens of Example 1 Aberration diagram of Example 1 at f = 10.30 mm and an object distance of 3 m Aberration diagram of Example 1 at f = 39.45 mm and an object distance of 2.5 m Aberration diagram of Example 1 at f = 151.10 mm and an object distance of 2.5 m Aberration diagram of Example 1 at f = 151.10 mm and an object distance of infinity. Aberration diagram of Example 1 at f = 151.10 mm and an object distance of 1 m Sectional view of the zoom lens of Embodiment 2 of the present invention at the wide-angle end Aberration diagram of Example 2 at f = 11.30 mm and an object distance of 5 m Aberration diagram of Example 2 at f = 43.84 mm and an object distance of 5 m. Aberration diagram of Example 2 at f = 169.52 mm and an object distance of 5 m Aberration diagram of Example 2 at f = 169.52 mm, at an object distance of infinity. Aberration diagram of Example 2 at f = 169.52 mm and an object distance of 1 m Conceptual diagram when the third lens unit has negative refractive power in the zoom lens of the present invention Conceptual diagram when the third lens unit has a positive refractive power in the zoom lens of the present invention. Schematic diagram of a main part of a video camera having a zoom lens of the present invention Schematic diagram of essential parts of a digital camera having a zoom lens of the present invention

Explanation of symbols

L1 1st lens group L2 2nd lens group L3 3rd lens group L4 4th lens group L4a 4a lens group L4b 4b lens group L4c 4c lens group sh Image size conversion optical system SP Aperture stop P Glass block IP Image surface d d line g g line ΔM meridional image plane ΔS sagittal image plane f focal length ω half angle of view Fno F number

Claims (13)

In order from the object side to the image side, a first lens group having a positive refractive power, a second lens group having a negative refractive power, a third lens group having a positive or negative refractive power, and a fourth lens group having a positive refractive power. In the zoom lens in which the second lens group and the third lens group move during zooming, the fourth lens group includes, in order from the object side to the image side, a 4a lens group, a 4b lens group, 4c lens group, when the 4b lens group moves on the optical axis to perform focusing, and the imaging magnification of the 4c lens group is β4c,
| Β4c |> 1
A zoom lens characterized by satisfying The third lens group has a negative refractive power, and when zooming from the wide-angle side to the telephoto side, the second lens group moves on the optical axis from the object side to the image side, and the third lens group moves on the optical axis. 2. The zoom lens according to claim 1, wherein the zoom lens moves toward the image side after moving toward the object side. The third lens group has a positive refractive power, and during zooming from the wide angle side to the telephoto side, the second lens group moves on the optical axis from the object side to the image side, and the third lens group is on the optical axis. 2. The zoom lens according to claim 1, wherein the zoom lens moves from the image side to the object side and passes through a zoom position in which the imaging magnification is −1. When the imaging magnification of the 4b lens group is β4b,
| (1-β4b ² ) · β4c ² |> 1
The zoom lens according to claim 1, wherein the zoom lens satisfies the following. 5. The zoom lens according to claim 1, wherein focusing is performed by moving the whole or a part of the first lens group on an optical axis. 6. The zoom lens according to claim 5, wherein flange back adjustment is performed by moving all or a part of the fourth lens group on the optical axis. The image forming magnification at an arbitrary zoom position in the entire system is β, the image forming magnification of the first lens group is β1, and the image forming magnification β in a state where focusing by the 4b lens group is not performed is β = 0 and β1 The position on the optical axis of the first lens group where = 0 is the reference position x0, the imaging magnification by the lens group after the second lens group is β ₂₃₄ , the F number of the entire system is F, and the minimum circle of confusion diameter is When δ, the position x on the optical axis of the first lens group is | (x−x0) · (β ₂₃₄ ) ² / (δF) | <1.
The zoom lens according to claim 5 or 6, wherein when the above condition is satisfied, focusing by the fourth lens group is performed. In the fourth lens group, an image size conversion optical system sh that can be inserted and removed is provided on the object side of the fourth lens group, and the conversion magnification is βsh,
βsh <1
The zoom lens according to claim 1, wherein: The maximum extension amount of the 4b lens group when the image size conversion optical system sh is inserted into the optical path is shmax, and the maximum extension amount of the 4b lens group before the image size conversion optical system sh is inserted into the optical path. Is smax,
0.9 <shmax / (βsh ² · smax) <1.1
The zoom lens according to claim 8, wherein: When the 4b lens group has a positive refractive power and the 4c lens group has a negative refractive power, and the imaging magnification of the 4b lens group is β4b,
−0.3 <β4b <0.3
The zoom lens according to claim 1, wherein: The zoom lens according to claim 10, wherein the fourth c lens group includes one lens having negative refractive power. The zoom lens according to claim 1, wherein the zoom lens is an optical system for forming an image on a solid-state imaging device. An image pickup apparatus comprising: the zoom lens according to claim 1; and a solid-state image pickup device that receives an image formed by the zoom lens.