JPS58214119A - Zoom lens capable of ultra-closeup photography - Google Patents

Abstract

PURPOSE:To ensure the ultra-closeup photogaphy with good image forming performance, by forming a relay lens with a front group and a rear group, forming the rear group with positive and negative lens groups along with the lenses preceding the positive lens group formed into an afocal system as a whole and shifting forward the positive lens group. CONSTITUTION:A focusing lens group G1 having positive refractive power, a variable magnification lens group G2 having negative refractive power, a compensator group G3 of negative refractive power and a relay lens group G4 consisting of front and rear groups G41 and G42 are set successively from the side of a subject. The group G42 contains a negative lens group GN and a positive lens group GP from the side of the subject, and the lenses preceding the group GP are formed into an afocal system as a whole. Then the group GP is set close to the front lens system along the optical axis as shown in the figure. Thus the ultra-closeup shooting is carried out over the entire zooming range. In this case, no variation is virtually produced for the spherical aberration owing to the shift of the group GP along with reduced variations of other aberrations.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a zoom lens capable of extremely close-up photography, and particularly to a zoom lens for a color video camera having a large aperture and a high variable magnification.

Regarding the ultra-close-up shooting method, which takes pictures of objects even closer to the lens than the normal close-up distance, conventional approaches include (1) a method in which the lens group in front of the relay lens group is moved together; (2) variable magnification; A method of moving one or both of the lens group and the image plane position correction lens group, and (5) a method of moving the front group of the relay lens group are well known. 526
No. 35 and Japanese Unexamined Patent Publication No. 50-65919. (2)
Related publications include JP-A-51-2459, JP-B-50-23814, and JP-A-49-55852. In both of these two systems, since the variable magnification lens group is moved relative to the relay lens group, aberration fluctuations are large, and good imaging performance during extremely close-up photography cannot be expected. Moreover, since the aperture position is usually placed in the relay lens group or just in front of the relay lens group, the above (1)
, The position of the entrance pupil changes during ultra-close-up photography using the method (2). Therefore, when performing super close-up photography on the wide-angle side, the entrance pupil moves toward the image side, so the position where the principal light at the maximum image height passes through the foremost lens surface is further away from the optical axis, ensuring sufficient peripheral light intensity. However, this method has the disadvantage of increasing the aperture of the front lens. Furthermore, in method (1), it is necessary to provide a separate mechanism to move the focusing lens group with a movable mechanism for focusing and the lens group with a movable mechanism for zooming as one, making it mechanically complex. I have no choice but to do so. In method (2), mechanical complexity can be avoided by creating a groove for moving the lens group during ultra-close-up photography on the extension of the cam groove for zooming, but ultra-close-up photography is It is limited to the extreme or telephoto end. In order to enable extremely close-up photography over the entire zooming range, it becomes mechanically complex, similar to method (1), and furthermore, it is necessary to set up a movement space for extremely close-up photography that is not necessary during zooming. , the entire lens system becomes larger.

In addition, in general, in zoom lenses for color video cameras, the exit pupil must be placed sufficiently far from the image plane, and if the power arrangement of the relay lens group is determined to satisfy this requirement, the refractive power of the front group of the relay lens will be The refractive power of the rear group will also be much larger. Moreover, the variable power and correction lens system located in front of the relay lens is often a diverging system, and therefore the lens aperture of the front group of the relay lens is larger than that of the rear group. When ultra-close-up photography is performed using method (3) with a zoom lens with such a power arrangement, aberration fluctuations occur because the lens group with large refractive power is moved so that the light flux in front and behind it is in a state of strong divergence and convergence. Large and good imaging performance cannot be maintained. Furthermore, since a large lens group is moved, it is disadvantageous in terms of mechanical precision. (Japanese Patent Publication No. 48-52587 is known as a zoom lens that performs close-up photography using a phantom method, but the example disclosed here is a 6m cine camera with a zoom ratio of 2.5 times and an F number of 1.8. It is a zoom lens for use in the field of photography, and has only an extremely small magnification ratio.

An object of the present invention is to provide a zoom lens that has good imaging performance not only during normal shooting but also during super close-up shooting, is mechanically simple, and is capable of super-close shooting over the entire zooming range. be.

The present invention includes, in order from the object side, a focusing lens group (G1) with positive refractive power, a variable magnification lens group (G2) with negative refractive power, and an image plane position correction lens group (Gs) with negative refractive power. , and a relay lens group (Gll) having a front group (G111) and a rear group (Gu), the relay lens rear group (G□) is connected to a negative lens group (GN
), the positive lens group (Gp ), and the positive lens group (O
p) The entire lens in front of this is configured to be almost an afocal system, and by bringing the positive lens group (GP) relatively close to the lens system in front of this with respect to the optical axis, It performs extremely close-up photography over the entire zooming range. Since the state between the negative lens group (GN) and positive lens group (Gp) of the relay lens rear group (G%t) is close to a parallel beam system, the fluctuation of spherical aberration due to the movement of the positive lens group (Gp) is rare.

Furthermore, since the amount of movement is small, fluctuations in astigmatism and distortion are also small, and fluctuations in the exit pupil position are not a problem. What's more, you can take very close-up shots in any position from the wide-angle end to the telephoto end, and you can adjust the shooting distance depending on the zooming state. A distant person is focused by the focusing lens group (G1), a person in the foreground is focused by the positive lens group (Gp) in the rear relay lens group, and a positive lens group (op) in the rear relay lens group is focused. Instantaneous movement enables a so-called focus shifting photography technique in which the focus of the two is switched.

In the basic configuration of the present invention as described above, the focal length of the entire lens system at the telephoto end is fl·, and after the relay lens #
The focal length of (G, , ) is '42, negative lens group (GN) and positive lens group CGP in the relay lens rear group (G, ))
The distance between the lens surfaces and the lens surface is , and the focal length of the positive lens group CGp is tp.

The distance from the rear principal point of the positive lens group (Gp) to the υ image plane is B
Therefore, it is important to satisfy the following conditions.

p p 0.7 < - < 1.5 The C5 condition (1) satisfies the specific requirement for lenses for color video cameras that the exit pupil is placed sufficiently far from the image plane. Condition (1
) Exceeding either the upper or lower limit causes the exit pupil to approach one quadrant surface too much, causing color shading.

Furthermore, if the lower limit is exceeded, the relay lens rear group (()
Gp).

Condition (2) is a condition for securing a movable space for moving the positive lens group (GP) in the relay lens rear group CG, t), and if the lower limit is exceeded, the ultra-close shooting distance will be sufficiently shortened. Moreover, it becomes impossible to increase the photographing magnification. If the upper limit is exceeded, the back focus will become longer than necessary, and the overall length of the lens will therefore become longer.

Further, the position where the off-axis light beam passes through the positive lens group is away from the optical axis, and the aperture of the positive lens group becomes large.

Condition (3) is a condition for maintaining the entire lens system in front of the positive lens group (GP) in the rear group (0, 2) of the relay lens in a state close to a 7-focal system. When the lower limit is exceeded, the lens system in front of the positive lens group becomes a strongly divergent system,
When the upper limit is exceeded, the lens becomes a strongly convergent system, and in either case, fluctuations in spherical aberration, coma aberration, and field curvature become large, and good focusing performance is maintained both during normal shooting and during ultra-close shooting. becomes difficult.

In the above configuration, after the relay lens U#CG*
The negative lens group (GN) in t) consists of a negative lens with a surface with a stronger curvature facing toward the image plane, and the positive lens group (Gp) consists of two biconvex lenses or one biconvex lens and one biconvex lens. It is desirable that the lens be constructed from a laminated lens. With this configuration, the above conditions (1) to (5) can be easily satisfied while maintaining good imaging performance.

Examples of the present invention will be described below.

Table 1 shows the structural specifications of the first embodiment. Common to all 6 tables, the No. at the left end of the table indicates the order from the object side. spear 1
The figure is a cross-sectional view of the lens of the first embodiment in the state of photographing an object at infinity at the wide-angle end. Figure J.2 is a plan view of the lens Fυ during extremely close-up photography at the wide-angle end according to the method of the present invention. After the relay lens! Western positive lens group CGp) 1.5 on the object side
When moved by u, wide-angle end (f = 9.65mm), middle 1
iJJ (f = 34.5 xm), telephoto end (f =
12! L50) The distance S from the surface of the lens to the object and the photographing magnification β during extremely close-up photography at each position i are as follows.

Figure 3 shows aberrations at the wide-angle end, Figure 4 shows aberrations at the telephoto end when shooting at infinity, and Figures 3 and 5 show aberrations at the wide-angle end when shooting at very close range.

fT 1)4 - = 0.197 P P - = L1.848 For comparison, a case will be shown in which very close-up photography is performed by moving the relay lens front group (G4.) to the image side. When the displacement of the front relay lens group (04,) is 1.5 degrees, the 1w point distance S and the magnification β at each zooming position are as follows.

FIG. 6 shows various aberration diagrams in a very close-up photographing state using this method at the wide-angle end. 8ph in the aberration diagram is spherical aberration, As
t stands for astigmatism, Dis stands for distortion, and the sine condition is also shown with a broken line in the two-spherical aberration diagram. However, the aberration diagrams shown in Figure 2 show the state that has been corrected by taking into consideration various parallel plane plates such as a stripe filter, a face plate, and a high frequency cut filter placed between the lens and the imaging surface (see the following example). (The same applies to) As shown in the above numerical values and drawings, almost the same photographic distance doubling ratio can be secured with the same amount of movement as with the two-way type.

The variations in spherical aberration and distorted aberration caused by variations in aberrations are significantly smaller in the case of the present invention.

Table 2 shows the structural specifications of the second embodiment. FIG. 7 is a cross-sectional view of the lens of the second embodiment in the state of photographing an object at infinity at the wide-angle end. FIG. 8 is a cross-sectional view of the lens during extremely close-up photography at the wide-angle end according to the method of the present invention. When the positive lens group of the rear relay lens group is moved 2.5 degrees toward the object side, the wide-angle end (r=
11.74i! jI) to intermediate (f=32.48),
The distance ゛S from the first surface of the lens to the object and the photographing magnification β during extremely close-up photography at each position at the telephoto end (r=s92u) are as follows.

Figure 9 is at the wide-angle end. Further, FIG. 10 shows an aberration diagram when photographing at infinity at the telephoto end, and FIG. 11 shows an aberration diagram when photographing at a very close distance at the wide-angle end.

f42 − = 0. E190 T 4 =0.185 P P -= 0.976 Also in this example, for comparison, the relay lens front group (
G4. ) is moved 6.20 degrees to the W side to perform super close-up photography. At this time, the object point distance S and magnification β at each zooming position are as follows.

As shown by the above numerical values, the method according to the present invention can secure the same photographing distance with a smaller amount of movement, and can also achieve a larger photographing magnification.

Figure 12 is an aberration diagram during extremely close-up photography due to the movement of the relay lens front group (G41). As is clear from a comparison of Figures 11 and 12, the system according to the present invention can significantly reduce aberration fluctuations, particularly field curvature and distortion aberrations.

In addition, in general, during ultra-close-up photography, the position where the principal ray of maximum image height cuts through the front lens surface is farther away from the optical axis as the photography magnification decreases, and the aperture of the front lens must be made thicker. Because the object distance during ultra-close shooting is short and the magnification is high, the 6-lens lens is designed to keep the aperture of the front lens sufficiently small.

As described above, according to the present invention, the rear relay lens group is divided into a negative lens group and a positive lens group, the front lens system of the positive lens group is configured to be almost an afocal system, and the positive lens group This large-diameter, high-variable-magnification zoom lens has good imaging performance in both normal shooting and ultra-close-up shooting by moving the lens a minute amount toward the object side, and enables ultra-close-up shooting over the entire zooming range with simple operations. can be realized.

[Brief explanation of drawings]

Figure 1 is a cross-sectional view of the lens in the photographing state of an object at infinity at the wide-angle end using the embodiment of Figure 1. Figure 2 is a cross-sectional view of the lens during extremely close-up photography at the wide-angle end using the method of the present invention. Diagrams of various aberrations when shooting at infinity at the wide-angle end, Figure 4 is a diagram of various aberrations when photographing at infinity at the telephoto end, Figure J' 5 is a diagram of various aberrations when shooting at extremely close-up at the wide-angle end, Figure 6 is a diagram of the book Figure 7 is a cross-sectional view of the lens in the state of photographing an object at infinity at the wide-angle end of the second embodiment; Figure 9 shows various aberrations when shooting at infinity at the wide-angle end. Figure 10 shows various aberrations when shooting at infinity at the telephoto end. Figure 11 The figure shows various aberrations during very close-up shooting at the wide-angle end, and Figure 12 shows various aberrations during very close-up shooting due to the movement of the front group of the relay lens. [Explanation of symbols of main parts] Focusing lens group −−−−−−−−−−−−−−−−==
----------G. Variable magnification lens group −−−−−−−−−−−−−−−−−−
−−−−−−−−−−−−−G2 image plane position correction lens group −−−−−−−−−−−−−−−−−−−−G. Relay lens group −−−−−−−−−−−−−−−1'
−−−−−−−−−−−G.

Claims (1)

[Claims] From the object side: +1 focusing lens group with positive refractive power, variable magnification lens group with negative refractive power, image plane position correction lens group with negative refractive power, relay lens front group with positive refractive power and a zoom lens composed of a relay lens rear group having positive refractive power, the relay lens rear group is composed of a negative lens group and a positive lens group in order from the object side, and the relay lens rear group is composed of a negative lens group and a positive lens group in order from the object side. When focusing on an object, focusing is performed by moving the focusing lens group, and when focusing on an object at a shorter distance than the predetermined short distance, the positive lens in the rear relay lens group A zoom lens capable of extremely close-up photography, characterized in that focusing is achieved by moving a group in the optical axis direction relative to a lens system in front of it.