JPS61123811A - Zoom lens - Google Patents

Abstract

PURPOSE:To maintain stable and superior image formation performance over a wide power variation range with simple constitution by providing a lens system of four-group constitution with the 2nd nonlinear moving lens which has a different movement track from a compensating lens group, and satisfying specific conditional expressions. CONSTITUTION:When the lens system of four-group constitution is varied in power from its wide-angle end W to its telephone end T, the 1st group G1 moves linearly toward the object side and the 2nd group G2 is fixed; and the 3rd group G3 moves nonlinearly for image plane compensation and the 4th group G4 moves as the 2nd nonlinear moving group. For example, an image-side lens group constituting an focal part has power betaR in the power variation range and the specific expressions I and II hold for the coefficient K of the quantity of movement of the lens group. The astigmatic and coma aberrations are therefore varied by varying the gap of the afocal part without varying the spherical aberration and the image formation performance which is stable and superior over the wide power variation range is obtained with the simple constitution.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field of the Invention) The present invention relates to a zoom lens with a high zoom ratio, and particularly to a zoom lens that can satisfactorily correct aberration fluctuations in a wide zoom range.

(Background of the Invention) In recent years, as the magnification of zoom lenses has been increasing, aberration fluctuations due to zooming have become a major problem in design, in addition to short-range fluctuations in aberrations due to focusing. It is difficult to properly correct both of these aberration fluctuations, and in particular, the higher the degree of high magnification, the more remarkable the aberration fluctuations are. Maintaining performance was extremely difficult. In order to correct such aberration fluctuations due to zooming, it is possible to configure the movable lens group for zooming with more lenses or increase the number of lens groups. The drawback of this was that the lens system had a complicated structure and was large.

(Object of the Invention) An object of the present invention is to provide a zoom lens that can stably maintain excellent imaging performance over a wide variable power range with a relatively simple configuration.

(Summary of the Invention) The present invention has a structure in which the lens group, which moves linearly with respect to the lead group when changing magnification in a conventional zoom lens, moves nonlinearly, so that the light flux passing through the lens system is almost aligned. By changing the distance between the focal groups, it is possible to effectively correct aberrations, particularly fluctuations in astigmatism and coma aberration. In other words, it consists of a plurality of lens groups, including a lead lens group that moves linearly with respect to the image plane during zooming, and a correction lens group that moves nonlinearly with respect to the image plane. In a zoom lens having a group spacing such that a light beam passing through the lens group spacing becomes afocal (hereinafter simply referred to as an afocal portion), a second nonlinear moving lens that has a movement trajectory different from that of the correction lens group. The structure is such that a group is provided and the distance between the afocal parts is changed as the magnification is changed.

In the present invention, the afocal part means the interval between lens groups where the light flux passing through the lens system becomes a parallel light flux, and is not limited to the case where the light flux passing through the lens system becomes a completely parallel light flux. This also includes cases in which the beam becomes a completely parallel beam only in the range of , or in the vicinity outside the zooming range, but does not become a completely parallel beam in other conditions.

To explain in more detail with reference to the example of the zoom lens with a four-group configuration shown in FIG. At this time, the lens group G1 moves linearly toward the object side with respect to the image plane I (referred to as a lead lens group), and the third lens group G,
moves non-linearly toward the object side to correct the image plane position, the fourth lens group G4 moves linearly toward the object side as shown by the dotted line, and the second lens group G8 moves toward the image plane. Fixed. Such a zoom lens has already been commercialized, but in the present invention, in such a configuration, as shown in the figure, the third lens group G is connected between the wide-angle end W and the telephoto position #iT.
, and the fourth lens group G become parallel light beams, and found that aberration fluctuations due to zooming can be favorably corrected by changing this interval during zooming. For this purpose, in order to change the distance between the afocal parts, in the case of a lens group that does not conventionally move non-linearly, that is, in the example of FIG.
As shown by the solid line in the figure, the fourth lens group G4 is newly moved in a non-linear manner.

Even if the distance between the lens groups in the afocal area changes, the light beam from the on-axis (including infinity) object point will not be reflected by the lens group on the image plane forming the afocal area (the fourth lens group in Figure 1). G
, ) remains unchanged, so the spherical aberration does not change.On the other hand, for the light beam from off-axis, the afocal part also has an angle to the optical axis, so this interval is When this changes, the height of the incident light on the lens group on the image side changes, so astigmatism and coma aberration change.

Therefore, by changing the spacing between the afocal parts, it is possible to change astigmatism and coma aberration without changing spherical aberration. However, simply changing the interval between the afocal parts is not practical because it destroys the conjugate relationship between the object point and the image point or increases the number of movable groups.

In the following, the present invention will be explained in detail based on FIG. 2, taking as an example a method of making the fourth lens group G4 non-linear with reference to the wide-angle end and the telephoto end in the four-group zoom lens shown in FIG. Explain in detail.

The focal length of each of the second lens group G2, third lens group G, and fourth lens group G4 is F+
, F□Fx, Fa. The lead group, Luns group G
, the amount of movement from the wide-angle end W is Let them be β5 and β4, respectively.

In addition, the amount of displacement of the fourth lens group G due to nonlinearization, that is,
The amount of deviation from the straight line connecting the wide-angle end and the telephoto end is ΔX, the magnification used is β49, the amount of displacement of the third lens group G, which is the image plane correction group, is Δy, and the nonlinearity of the fourth lens group G9 is The magnification used by the third lens group G after the transformation is assumed to be β1. However, since the lens group Gl and the second lens group G do not need to be displaced due to nonlinearization, β2 remains unchanged. . At this time, β, 7, and β47 are β. =β, −−(1) F.

β, R-(2) Fgo/β, +Δy It can be expressed as

On the other hand, before the fourth lens group G0 is made nonlinear, the distance from the image point created by the second lens group Gt to the image point created by the fourth lens group G4 is βgo, βa, Fs
, Fa, and similarly, the distance LTl after nonlinearization becomes. The image point by the second lens group G and the image point by the fourth lens group G6 must both coincide with each image point before conversion. Therefore, L
It is necessary to perform nonlinearization so that the following relationship holds.

By the way, the focal length with respect to the position of
at! ,! −・
. (f(x I) =F+ ・8g ・β2
'β, (6) fn(x l) =F+ ・β8 ・
β1.・β, , (7) Substituting equations (1) and (2) gives us, which means that the focal point corresponding to the same amount of lead movement X+ before and after the nonlinearization of the fourth lens group G# This means that the distance value will change.

From the above, in actual nonlinearization, the amount of movement of the lens group Gl as a lead group corresponding to the same focal length differs from X to Xl1l. and,
In FIG. 2, the focal length state f(
x () and the focal length shape afn (after nonlinearization of (b))
As can be seen from the comparison with x +−) −f(χ,),
Due to nonlinearization, the distance C of the "afocal part" changes to C7 at the same focal length, and the other group distances a,
It must be noted that b also changes to a@, b, and l, respectively.Of course, the focal length f(
X! ) is a value different from the focal length 11fn(x t ) at the same movement amount X of the lens group G1 after nonlinearization.

Therefore, when performing such nonlinearization in an actual zoom lens, other group spacing changes accompanying changes in the "afocal part" spacing necessary to suppress zooming fluctuations at a given focal length must be considered. It is necessary to select the group to be nonlinear while considering the influence on aberrations.

To this end, in the present invention, the lens group that moves linearly in the conventional configuration is made into a second lens group that moves nonlinearly, in addition to the nonlinearly moving lens group for image plane correction. In addition, the image side lens group constituting the afocal portion has a configuration that satisfies the following conditions with respect to the magnification β in the variable power range, the linearly moving lead lens group, and the second nonlinear moving group. This is what I did.

1β++ l < 0.6 (a) However, based on the wide-angle end of the entire system, x: Amount of movement of the lead lens group at the telephoto end of the entire system Yt: Movement of the second nonlinear moving lens group at the telephoto end Amount x 1 = Amount of movement of the lead lens group at an arbitrary total system focal length f: Amount of movement of the second nonlinear moving lens group fl at an arbitrary total system focal length 1lII f t: Total distance at the wide-angle end is the composite focal length of the system, K
t"Yy/XtKt-Yr/X+.

If the above condition (a) is not met, variations in aberrations other than astigmatism, especially spherical aberration, will increase due to changes in the spacing of the afocal parts, and the independent correction of astigmatism, which is the objective of the present invention, will become large. Condition (b) becomes difficult.
If it deviates from this, the spacing between lens groups other than the afocal section will change significantly, and at the same time as the desired aberration is corrected by the afocal section, the aberrations will vary greatly in the spacing of other lens groups, so it will be difficult to correct various aberrations. The balance will be disrupted, making it difficult to maintain stable and high imaging performance over a wide range of variable magnification.

And, in the present invention, "as the afocal part J,
It is desirable that the magnification β carried by the object-side lens group constituting this group interval satisfies the condition 1βFl>2.0 within the zoom range.

If the above range is exceeded, all aberrations including spherical aberration will vary greatly when any group is rendered nonlinear, making it impossible to achieve the object of the present invention.

Furthermore, in the basic configuration as described above, the image-side lens group forming the afocal part has a magnification β in the variable power range.
If 0.4<lβ*l<0.6 (C), it is desirable to satisfy the following conditions.

Note that for 1β, 1≦0.4, sufficiently good correction is possible within the range of condition (b) above.

(Example) Examples according to the present invention will be described below. The first embodiment is a zoom lens for an eye reflex camera.
The focal length is 71-1 to 243 mm, and the F number is 3.
58 to 4.58, and the fourth lens group G# is made nonlinear, similar to the example used in the previous theoretical explanation. That is, the zoom lens is made up of four groups, in order from the object side: a lens group G having positive refractive power, a second lens group G8 having negative refractive power, a third lens group G having positive refractive power, and a fourth lens group. When changing the magnification from the wide-angle end to the telephoto end, the second lens group G1 moves linearly toward the object side, and the second lens group G1 moves linearly toward the object side.
! is fixed with respect to the image plane, the third lens group G2 moves nonlinearly toward the object side to correct the image plane, and the fourth lens group G4 moves toward the object side as a second nonlinearly moving group. It moves non-linearly towards the target. In the first embodiment,
The fourth lens group G9 has been made non-linear, and the non-linear movement curves of the third lens group G have also changed accordingly, and the final movement curves of each group are as shown in FIG. The solid line in FIG. 3 is the movement curve of the fourth lens group G0 after nonlinearization, and the dotted line represents the movement of the fourth lens group G0 before nonlinearization. A lens configuration diagram of the first embodiment and a movement curve after nonlinearization are shown in FIGS. 4A and 4B, respectively.

The specifications of the first embodiment are shown in Table 1 below. In the table, the leftmost number represents the order from the object side, and the refractive index and A7be number are d
The value for the line (λ = 587.6rv) is the surface soil m01 salmon focal length f = 71.0~243. OF number 3.5
Next, Table 2 shows the amount of change in group spacing before and after nonlinearization in the first example.

In addition, each value in this table is for each group interval before nonlinearization.
The case where each group interval increases after nonlinearization is shown as positive. From this table, we can see that the second
Lens group G! The amount of change Δ in the group spacing between and the third lens group G3
It can be seen that dl+ is smaller than other group spacing changes. In the zoom lens according to the first embodiment, the distance between the second lens group G and the third lens group Gs has a very large effect on aberrations, and the distance between the second lens group G and the third lens group G
The amount of change Δd in the group spacing between the third lens group G and the fourth lens group G as the "afocal section" has a smaller influence than the amount of change Δd0 in the group spacing between It meets the conditions for nonlinearization.

5A and 5B show aberration diagrams after nonlinearization of the fourth lens group Ga in the first embodiment for each focal length state, and FIGS. 6A and 6B show a comparison of the effects of the present invention. For this purpose, aberration diagrams before nonlinearization are shown for each focal length state.

Each aberration diagram is for an infinite object distance, and according to the spherical aberration diagrams, which also include the sine condition with a dotted line, the spherical aberration does not change much due to nonlinearization, It is clear that astigmatism and distortion aberration have changed, and that astigmatism and field curvature have been better corrected than before nonlinearization.

Table 3 shows the corresponding values of the above conditional expression (a) in each focal length state for the first embodiment.

l Main (Condition corresponding value: 1st example) The second example according to the present invention is used as a zoom lens for a camera with a focal length of 35.71 to 130.
．． 95mm, with an F number of 3.57 to 4.6, and as shown in the lens configuration diagram in Figure 7Δ, in order from the object side, the lens group G has a positive refractive power, the second lens group has a negative refractive power. Group G2. It consists of a third lens group G□ with positive refractive power and a fourth lens group G4 with positive refractive power. As shown in the movement trajectory in FIG. 7B, when changing the magnification from the wide-angle end to the telephoto end, the fourth lens RG4 and the fourth lens group G4 integrally move toward the object side, and the second lens group G2 moves nonlinearly, and the third lens group G is also moved nonlinearly. Table 4 below shows the specifications of the second embodiment.

-4(・2.) 4(:2) The aberration diagrams of the fourth lens group G4 after nonlinearization in the second embodiment are shown in FIGS. 8A and 8 for each focal length state.
Shown in Figure B.

Table 5 below shows the corresponding values of the above conditional expression (a) in each focal length state for the first embodiment.

The third embodiment is a zoom lens for a negative-eye reflex camera, and has a focal length of 28.8+n+ to 83.5+w-.
As shown in the lens configuration diagram in Figure 9A, the 6-group configuration with an F number of 3.51 to 4.47 includes, in order from the object side, the fourth lens RG4 with negative refractive power, and the fourth lens RG4 with positive refractive power. Second
It consists of a lens group G2, a third lens group G with a negative refractive power, and a fourth lens RG4 with a positive refractive power, and the fourth lens group G0 is made nonlinear based on the present invention.

That is, as shown in the movement trajectory in FIG. 9B, when changing the magnification from the wide-angle end to the telephoto end, the second lens group G moves nonlinearly toward the image side to correct the image plane position, and the second lens group G moves linearly toward the object side, the third lens group G is fixed with respect to the image plane, and the fourth lens group G4 also moves nonlinearly toward the object side.

6 (3rd example) Focal length f = 28.8 to 83.5 F number 3.
51 to 4.476 (ki: 3-) Aberration diagrams of the fourth lens group G4 after nonlinearization in the third embodiment are shown in FIG. 1OA and FIG. 10B for each focal length state.

Table 7 below shows the corresponding values of the above conditional expression (a) in each focal length state for the third embodiment.

The fourth embodiment of the present invention is a zoom lens for a -eye reflex camera with a focal length of 36m5 to 102m.
+w and an F number of 3.36 to 4.6.

As shown in the lens configuration diagram in FIG. 11A, the lens group consists of, in order from the object side, the first lens group G with positive refractive power, the second lens group G with negative refractive power,
It consists of a lens group G2, a third lens group G3 with a negative refractive power, a fourth lens group G with a positive refractive power, and a fifth lens group G with a positive refractive power. In addition to the third lens group G, the fifth lens group G is also configured to be moved nonlinearly based on the present invention. As shown in the movement trajectory in Fig. 11B, when changing the magnification from the wide-angle end to the telephoto end, the lens group G and the fourth lens group G integrally move linearly toward the object side. The second lens group G2 is fixed with respect to the image plane, and the third lens group G and the fifth lens group G move nonlinearly toward the object side.

Table 8 shows the specifications of this fourth embodiment.

10A and 10B show aberration diagrams of the fourth lens group G4 in the fourth embodiment after nonlinearization for each electric point distance state.

The following Table 9 shows the corresponding values of the above conditional expression (a) in each focal length state for the fourth embodiment.

From the various aberration diagrams of the above examples, it is clear that all examples maintain stable and excellent imaging performance over the entire magnification range, and the nonlinearization according to the present invention is effective. It turns out that.

By the way, in the above embodiment, in giving the second nonlinear movement to a lens system having an afocal part, it is assumed that aberration fluctuations between the wide-angle end and the telephoto end of the variable power range are taken as a reference. However, in reality, at the wide-angle end,
It can be applied to any focal length including the telephoto end. When the reference point is set outside the zoom area, it becomes possible to correct aberration fluctuations over the entire zoom area.

That is, the basis of nonlinearization is not limited to the wide-angle end or the telephoto end.

This will be explained with reference to FIG. FIG. 13, like FIG. 2, illustrates the movement locus of a zoom lens having a four-group configuration. Before nonlinearization, in order to change the magnification from wide-angle to telephoto, the lens group G1 and the fourth lens group G4 are required.
moves linearly toward the object side, the second lens group G is fixed with respect to the image plane, and the third lens group G moves nonlinearly to correct the image plane position. Here, a base point for non-linearization is set at iR at a position away from the wide-angle end of the variable power range, and correction is performed in the entire variable power range including the wide-angle end and the telephoto end. By providing this reference point R, the imaging point can be kept constant before and after nonlinearization. That is, before nonlinearization, the magnification was varied in the range from the wide-angle 4w to the telephoto end T shown in the figure, but when the movement amount of the lens group G1 is X from the reference position, the focus of the entire system is Since the distance changes from f(x+) to rn (Xl), which is different from f(x+), before and after nonlinearization of the fourth lens group G, even when changing the magnification within the same focal length range, the difference due to nonlinearization is The area used for zooming changes from wide-angle end W7 to telephoto end T. The range is up to. In this case, the aforementioned equations (1) to (5) hold as they are, and equations (6) to (8) express the movement I of the lead lens group.
X.

The same holds true by measuring from the reference position 1iR.

Note that the straight line passing through the wide-angle end and the telephoto end, which is the basis of conditional expression (a), is different from the straight line before nonlinearization passing through the reference point R in this case. However, considering that the lens specifications, that is, the curvature of the lens surface, the lens thickness, the air spacing (excluding the group spacing), and the refractive index, are exactly the same before and after nonlinearization according to the present invention, the final movement It is thought that there are an infinite number of straight line trajectories leading to the curve before nonlinearization, and even if all of them are represented by one straight line, that is, the straight line connecting the wide-angle end and the telephoto end of the final movement curve, there is no contradiction. It can be said that there is no. Therefore, even if the criterion for nonlinearization is arbitrarily selected, conditional expression (a)
is valid.

As mentioned above, in the sense of taking zooming fluctuations,
By mainly changing the group spacing in the "afocal part" and applying nonlinearization to groups that do not change the group spacing that affects the total aberrations much, aberration fluctuations during zooming can be effectively corrected. It goes without saying that the present invention can be applied to any zoom lens that has a group spacing that can be considered as an "afocal section."

(Effects of the Invention) As described above, according to the present invention, there is no need to complicate the configuration of each lens group in a conventional zoom lens, and there is no need to increase the number of lens groups. It is possible to achieve a zoom lens that maintains stable and excellent imaging performance over a wide range.

[Brief explanation of drawings]

FIG. 1 is a diagram illustrating a movement trajectory for zooming a zoom lens according to the present invention, FIG. 2 is an explanatory diagram illustrating a method of making a lens group nonlinear according to the present invention, and FIG. 3 is a diagram illustrating a method according to the present invention for making a lens group nonlinear. Fig. 4A is a lens configuration diagram of the first embodiment, and Fig. 4B is a diagram showing the movement trajectory for zooming in the first embodiment before and after nonlinearization. Figures 5A and 5B are diagrams of various aberrations at each berth distance state in the first embodiment, and Figures 6A and 6B are the first diagram for comparison. Various aberration diagrams at each focal length state before nonlinearization in the embodiment, FIG. 7A is a lens configuration diagram of the second embodiment, and FIG. 7B is after nonlinearization for zooming in the second embodiment. Movement trajectory diagram, Figure 8A and Figure 8B
The figure is a diagram of various aberrations at each focal length state in the second embodiment,
FIG. 9A is a lens configuration diagram of the third embodiment, and FIG. 9B is a lens configuration diagram of the third embodiment.
Movement locus diagram after non-linearization of the magnification changer in the example,
FIG. 10A and ILIOB are each j in the third embodiment.
Various aberration diagrams in the Q focal length state, FIG. 11A is a lens configuration diagram of the fourth embodiment, FIG. 11B is a movement locus diagram after nonlinearization for zooming in the fourth embodiment, and FIGS. 12A and 12
Figure B is a diagram of various aberrations in each focal length state in the fourth embodiment, and Figure 13 is an explanatory diagram when the reference position for nonlinearization is set outside the variable power range. (Explanation of symbols of main parts) G,... 2nd lens group G8 - 2nd lens group G, 3rd lens group G4... 4th lens group

Claims (1)

[Claims] Consisting of a plurality of lens groups including a lead lens group that moves linearly with respect to the image plane during zooming and a correction lens group that moves non-linearly with respect to the image plane, Alternatively, in a zoom lens having a lens group interval in which the passing light beam becomes afocal in the vicinity thereof, the afocal interval is changed by providing a second nonlinear moving lens group having a movement locus different from that of the correction lens group. A zoom lens characterized in that it has a configuration that satisfies the following conditions: |β_R|<0.
6 K_i−K_r≦｜[exp(f_w/f_i)]/1
0 | However, based on the wide-angle end of the entire system, X_r: Movement amount of the lead lens group at the telephoto end of the entire system Y_r: Movement amount of the second nonlinear moving lens group at the telephoto end Amount of movement of the lead lens group at distance f_i: Amount of movement of the second nonlinear moving lens group at an arbitrary focal length of the entire system f_i: Amount of movement of the second nonlinear moving lens group at a distance f_i: A synthetic focal length of the entire system at the wide-angle end, K
It is assumed that _r=Y_r/X_r K_i=Y_i/X_i.