JPH01130118A - Photographic lens for macro-close-up - Google Patents

Abstract

PURPOSE:To obtain a photographic lens for macro-close-up of a high magnification which is small in extending quantity, is long in working distance and is bright by constituting the lens of a front lens group having a positive refracting power and a rear lens group having a negative refracting power and constituting the lens so as to satisfy specific conditions. CONSTITUTION:This lens is constituted, successively from an object side, of the front lens group having the positive refracting power and the rear lens group having the negative refracting power and is so constituted as to satisfy the conditions expressed by inequalities I, II. In inequalities, f1 is the combined focal length of the front lens group having the positive refracting power; f2 is the combined focal length of the rear lens group having the negative refracting power. The lens is constituted, successively from the object side, of the front lens group having the positive refracting power and the rear lens group having the negative refracting power in such a manner, by which the front side main point position is approximated to the object side and the working distance is increased. In addition, the brightness and optical performance equal to the brightness and optical performance of a symmetrical type lens are obtainable.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a photographic lens used for close-up photography, particularly at high magnifications of 3x to 10x.

In general, when zooming in on this area, the higher the magnification, the more
The F number F becomes darker according to the following formula.

F=F,, (1+β) However, F: ■ F number when in focus β: ti shadow magnification (β>O) For example, when shooting at a high magnification of 10x with a lens with an F number of 2.8, It becomes dark with an F number of over 30. Furthermore, in order to perform high zooming such as 3x to over 10x with a single lens, the amount of lens extension (ΔX) is ΔX - fΔβ. If it were a photographic lens for magnified close-up photography, it would be 8X = 7 f, and the focal length could not be very long due to portability issues, so the working distance would be extremely short, which is undesirable. .

In other words, -i, a Gaussian (symmetrical) lens is used as a photographic lens for magnification and close-up photography, which is advantageous in correcting aberrations, but due to its symmetry, the principal point position is located approximately at the center of the optical system. , it becomes difficult to obtain a large working distance.

It has been known that in order to increase the working distance, a retrofocus type wide-angle lens is attached to the camera in the opposite direction to take enlarged close-up shots, but this method was originally designed for close-up shots. Therefore, it was difficult to obtain good image quality.

The present invention was made in order to solve the above-mentioned drawbacks, and it is an object of the present invention to provide a photographic lens for magnifying close-up photography with a small extension amount, a long working distance, and a bright high magnification. purpose.

Ben Yufu member! In order to achieve the above object, the present invention includes a lens having a front lens group having a positive refractive power and a rear lens group having a negative refractive power from the object side, and is configured to satisfy the following conditions. .

■0.80<f, /f<1.10■0.
90< l f 21 / f <1.25 However, ",: Composite focal length of the front lens group with positive refractive power f2: Composite focal length of the rear lens group with negative refractive power In this way, on the object side Therefore, by configuring the front lens group with a positive refractive power and the rear lens group with a negative refractive power, the working distance can be increased by bringing the front principal point closer to the object side.
Furthermore, it is possible to provide the same brightness and optical performance as a symmetrical lens.

When the lower limit of conditional expression (2) is exceeded, the positive refractive power of the front lens group increases, making it difficult to obtain a desired working distance.

On the other hand, if the upper limit is exceeded, the positive refractive power becomes small, making it difficult to correct aberrations. In particular, it is difficult to correct spherical aberration over the entire magnification range, resulting in either undercorrection on the low magnification side or extreme overcorrection on the high magnification side.

When the lower limit of condition (2) is exceeded, the negative refractive power of the rear lens group becomes strong and a sufficient working distance can be secured, but the asymmetry becomes strong and distortion and field curvature become large. On the other hand, if the upper limit is exceeded, the negative refractive power becomes weak, which deviates from the purpose of the present invention, which is to increase the working distance.

Furthermore, it is effective if the front lens group is composed of four components, positive, positive, negative, and positive, in order from the object side, and satisfies the following conditional expressions.

■ o, as< r I/ f <1.50■ 0.5
0<r3/f<0.95■0.65<I
r s l / f <1.65 (however, rs<0) ■
1.50< l r rv l / t rv<2.
50 (however, rIV<0) ■ 23 <1/, -v- However, r,: radius of curvature of the first surface from the object side rrv: the fourth
Radius of curvature on the image side of the positive component tIv: Axial center thickness of the fourth positive component v,: Average Atsube number of the positive lens in the front lens group v-: Average Abbe number of the negative lens in the front lens group Conditional expression ■, (2) defines the radius of curvature of the first and second positive components on the object side, and is a necessary condition for performing good aberration correction in the entire imaging magnification range. To divide each lower limit,
The amount of spherical aberration and field curvature that occurs increases. If the upper limit is exceeded, refractive power for sufficient aberration correction over the entire region cannot be obtained. Conditional expression 〇 defines the radius of curvature on the object side of the third negative component, and if it is below the lower limit, the amount of astigmatism and coma aberration will be large (if it exceeds the upper limit),
This makes it difficult to correct spherical aberration. When dividing the lower limit of conditional expression 〇, lrIVI becomes relatively small compared to tlV,
It becomes difficult to simultaneously reduce coma aberration and undercorrected spherical aberration on the low magnification side. If the upper limit is exceeded, lr
As IVl becomes relatively large compared to t+v, astigmatism becomes large, and spherical aberration also tends to be overcorrected. Conditional expression (2) is a necessary condition to satisfactorily correct longitudinal chromatic aberration and lateral chromatic aberration over all imaging magnifications.

Examples of the present invention will be shown below. In the examples, r1 to r1 are the radius of curvature of the lens surface counted from the object side, and d.

~d14 is the axis top surface interval counted from the object side, N1 ~ Nll
is the refractive index of the lens counted from the object side, and ~ν8 is the Abbe number of the lens counted from the object side.

r, 1.367 ds 0.080 -N+ 1.69680 ν
, 56.47r, 0.633 ds O,121Nt 1.74250 ν, 5
2.51r, 1.816 47 0.322 N41.78100 ν,
44.55rq O,506 ds 0.050 Ns 1.51680 ν
S 64.2Or,, -0,726 d++ 0.048 N41.51680 ν,
64.2 Orat -1,335 fl/f =0.858 l fit/f
=1.052r l/f =1.376r
s/f=0.633Irsl/f=1.
331 l rIVl/t+v=2.183v,
-V-=26.04'", 228 a+., .8o, 1□, 6968Q v
, 56.4□r:+0.583 dz O,124Nz 1.69350 ν, 5
3.39rs 1.411 ds O,084Ns 1.75000 ν, 25
．． 14r) 1.448 d, 0.322 Nm 1.7?250 ν449
．． 77re -0,494 ds o, oso Ns 1.51680 νs
64.20rll O, 753 a, 0.048 N, 1.51680 νb
64.2 Or+! -1,038 f, /f=0.874 1 fil/f=1.21
2r 1/f = 1.228 r:l/
f=0.5831 rsl/f=1.411
l rlvl /l+v=2.196V, -war=2
8.07 1j Ll Axis "J Drunken Plate Goko 1" σikud, 0.120 f+ / f=o, 970 1 ftl/f
=1.053r+/f=0.902
r3/f = 0.8741 rsl/f
=0.765 l rIV! /t+v=1.8
14V, -V-=28.07 Figure 1 shows the outline of the lens configuration corresponding to the above-mentioned Example 1, Figure 2 shows the aberration at 3 times the aberration, and Figure 3 shows the aberration at 10 times.
It shows the aberration during magnification. Figure 4 is a diagram of the lens configuration of Example 2, Figure 5 is the aberration at 3x, and Figure 6 is the aberration at 10x.
Each represents the aberration at the time of magnification. Further, FIG. 7 is a diagram showing the lens configuration of Example 3, FIG. 8 shows aberrations when the lens is magnified by 5 times, and FIG. 9 shows aberrations when the lens is magnified by 13 times. Furthermore, Figure 1,
FIG. 4 and FIG. 7 show the r1
- Also fill in r33, di""d14, etc.
. In the aberration diagrams in Figures 2, 3, 5, 6, 8, and 9, the solid line (d) represents the aberration for the d-line, and the dotted line (SC) represents the sine condition. . Further dotted line (DM)
and the solid line (DS) represent astigmatism on the meridional plane and the sagittal plane, respectively.

[Brief explanation of the drawing]

The figures are all related to the present invention; FIG. 1 is a lens configuration diagram of Example 1, and FIGS. 2 and 3 are aberration diagrams at different magnifications. FIG. 4 is a lens configuration diagram of Example 2, and FIGS. 5 and 6 are aberration diagrams at different magnifications. Figure 7 shows Example 3
FIG. 8 and FIG. 9 are aberration diagrams showing aberrations at different magnifications.

Claims (1)

[Claims] (1) From the object side, a front lens group having positive refractive power;
A high magnification close-up photographic lens that is composed of a rear lens group with negative refractive power and satisfies the following conditions: 0.80<f_1/f1.10 0.90<|f_2|/f<1.25 However, f: composite focal length of the entire system f_1: composite focal length of the front lens group f_2: composite focal length of the rear lens group (2) The front lens group has positive, positive, negative, and
0.85<r_1/f<1.50 0.85<r_1/f<1.500. 50<r_3/f<0.95 0.65<|r_5|/f<1.65 (however, r_5<0
) 1.50<|r_I_V|/t_I_V<2.50 (however, r_I_V<0) 23<@ν@＿+, -@ν@__- However, r_i: radius of curvature of the i-th surface from the object side r_I_V
: Radius of curvature on the image side of the fourth positive component t_I_V: Axial center thickness of the fourth positive component @ν@＿+: Average Abbe number of the positive lens in the front lens group @ν@＿−: Average of the Abbe number of the negative lens in the front lens group Average Abbe number