JPS63301916A - Rear conversion telephoto lens system - Google Patents

Abstract

PURPOSE:To obtain the titled lens system which has a good image surface property, and also, can be installed many lens system, and can correct enough an aberration even if it is installed to a large aperture telephoto lens, by constituting it of six pieces of lenses, and allowing it to satisfy a specific conditional expression. CONSTITUTION:The titled lens system consists of the front group and the rear group both having negative synthetic refracting power, and constituted of six pieces of lenses as a whole, and satisfies the conditions of an expression I. In the expression, fI:fII:RII-1:RII-2:RI-2-2:RI-2-3:D:- n1:and nui denote synthetic refracting power of the front group, synthetic refracting power of the rear group, a radius of curvature of an object side face of a negative lens in the rear group, a radius of curvature of an image side face of the negative lens in the group, a radius of curvature of an image face side of a negative lens in the second component of the front group, a radius of curvature of an object of a position lens in the second component of the front group, an air interval between the front and the rear groups, a refractive index of a negative lens of the first component of the front group, and an Abbe number of the i-th lens, respectively. In such a way, rear conversion telephoto lens system by which the image surface property is satisfactory and the object range of lens systems to which is can be installed is wide, and also, the aberration is corrected enough can be obtained.

Description

[Detailed Description of the Invention] R: radius of curvature of the object side of the negative lens in the rear group -1, R: radius of curvature of the image side of the negative lens in the rear group RI -2-
Radius of curvature on the image plane side of the negative lens (L3) in the 2" front group @22 component R1-2-3" Radius of curvature of the object of the positive lens (L, ) in the second component of the front group: Front/rear Air spacing between groups: refractive power of the negative lens (Ll) of the first component of the front group, and Abbe number of the i-th lens.

(2) The telephoto rear conversion lens system according to claim 1, wherein the negative lens of the first component and the biconvex lens are bonded together.

3. Detailed Description of the Invention The present invention relates to a rear conversion lens system that is attached to the image side of a photographic lens system to approximately double the focal length of the original lens. This relates to a conversion lens system.

A rear conversion lens system has a strong negative power because it is attached to the image side of a photographic lens system and expands the focal length of the lens system. For this reason, when a rear conversion lens system is attached, the Petzval sum of the entire lens system including the main lens system becomes a negative value with a large absolute value, which deteriorates image plane properties in particular. Therefore, in order to reduce the negative Petzval sum, it is possible to move the rear conversion lens system as close to the object side as possible, and to reduce the negative power of the rear conversion lens system as much as possible.
Its distance is limited due to mechanical interference with the main lens system. In other words, the distance from the focal position of the main lens to the first surface of the rear fusion lens system is -do(do>
O), the larger dO is, the closer the rear conversion lens system is to the main lens system. However, if dO is larger than the lens back of the main lens system to be installed, the main lens system and rear conversion lens system will collide, causing damage to the machine. It will not be possible to attach it. Therefore, there is a problem that the lower limit of the focal length of the target lens system that can be attached is determined by the value of dO.

On the other hand, recently, the performance of large-diameter telephoto lenses has been improved through the use of anomalous dispersion glass, and it has become necessary to improve the performance of the main lens attached to the lens without impairing it as much as possible.

Therefore, the present invention aims to provide a high-performance telephoto rear conversion lens system that has good image plane properties, can be attached to many lens systems, and has sufficient aberration correction even when attached to a large-diameter telephoto lens. purpose.

In order to achieve the above object, in the present invention, the front principal point of the rear conversion lens system is brought as close to the object side as possible without making dO too large. By keeping the power relatively low, the overall negative Petzval sum including the main lens is kept small. Also,
In order to be able to be attached to a large-diameter telephoto lens system with an open F value of up to F2, extroverted coma aberration around the screen, introverted coma at the center of the screen, and chromatic coma are corrected. That is, as is clear from FIGS. 1 to 3, the telephoto rear conversion lens system according to the present invention consists of a front group (1) and a rear group (II), both of which have a negative composite refractive power.

The front group (H) consists of a negative lens (L,) with a strongly concave surface directed from the object side to the image side, and a biconvex lens (F,) disposed on the image side.
2) and a biconcave lens (L
, ) and a positive lens (L, ) disposed on the image side.
It consists of component (1-2). The rear group (II) consists of a negative lens (F5) with a strongly concave surface facing the object side, and a biconvex lens (F6) disposed on the image side thereof.

In other words, it is composed of six lenses as a whole, and is characterized by satisfying the following conditional expression.

(1) 0.74<f, /f ■<2.5, (2
) 0.2<Rn-t/Rll-2<0, (3)
1.00<01.00<RI-2, /R1-2-3<1
．． 29(4) 0.10<D/Rn-x<o, 20
, (5) nl>1.8 (6) ν3−ν,>5. 0 However, f I: Composite focal length of the front group, f: Composite focal length of the rear group, ■ Rn-t: Radius of curvature of the object side of the negative lens in the rear group R: Image side surface of the negative lens in the rear group radius of curvature R1-2-2
"Radius of curvature on the image side of the negative lens in the second component of the front group, R1-2-3" Radius of curvature on the object side of the positive lens in the second component of the front group D: Air distance nl between the front and rear groups : Refractive index stain of the first component negative lens in the front group: Atsube number of the i-th lens.

The conditional expression will be explained below.

Conditional expression (1) stipulates an appropriate refractive power distribution in order to bring the front principal point of the rear conversion lens system closer to the object side and to balance the overall aberrations, especially coma and image plane properties. be. When the upper limit of conditional expression (1) is exceeded, the front principal point moves toward the image side, and the Petzval sum, which becomes negative, cannot be sufficiently corrected, resulting in worsening of image surface properties and increased astigmatism.

It becomes difficult to maintain. On the other hand, if the lower limit of conditional expression (1) is exceeded, it becomes difficult to correct coma aberration, and it becomes difficult to balance inward coma aberration at the center of the screen with outward coma at the periphery of the screen. Not suitable for

Conditional expression (2) is a condition for correcting coma aberration. If the upper limit of conditional expression (2) is exceeded, the correction of extroverted comatic aberration at the periphery of the screen becomes insufficient, and at the same time, off-axis chromatic aberration is likely to occur. Furthermore, if the lower limit is exceeded, it becomes difficult to correct inward coma aberration in the center of the screen.

Conditional expressions (3) and (4) are both conditions for correcting coma aberration and image surface properties. When the lower limit of conditional expression (3) is exceeded, it becomes difficult to correct chromatic coma aberration, and when the upper limit is exceeded, image plane properties deteriorate and astigmatism increases.

If the lower limit of conditional expression (4) is exceeded and the air distance between the front and rear groups becomes small, it becomes difficult to correct the inward coma aberration in the center of the image plane, and if the upper limit is exceeded, the image surface properties deteriorate and the The point distance difference increases.

Conditional expression (5) is a condition for good correction of image plane properties.By using high refractive index glass for the first lens (Ll), the negative Petzval sum of the entire system can be reduced and image plane properties can be improved. corrected to maintain high performance.

Conditional expression (6) is a condition for correcting Hosochi chromatic aberration and chromatic coma aberration. If the lower limit is exceeded, it becomes difficult to correct Hosochi chromatic aberration and chromatic coma while maintaining a balance even if the dispersion of other lenses is changed.

Note that in order to better correct chromatic coma aberration, it is desirable to satisfy 1.1<R/R 1-2-2J -2-3<1.29 (3)'.

In addition, in order to reduce errors in the air distance and radius of curvature between the first lens (L,) and the second lens (L2), it is desirable to construct the two lenses by bonding them together.

To provide a telephoto rear conversion lens system that satisfies the above conditions and has a wide range of wearable lens systems, well corrects aberrations, and has high performance enough to be applied to large-diameter telephoto lenses. Can be done.

Examples of the present invention will be shown below. Ll, L2 in the examples
L3... is the lens counted from the object side, r++r
2+r3... is the radius of curvature of the surface counted from the object side,
d,,d2. d, . . . indicate the distance on the axial surface counted from the object side. N,,N2. N,...is the th Runs (
L, ) to the refractive index of the sixth lens (L6), C1. C2.
Similarly, ν, . . . indicate the Abbe numbers of the lens (Ll) to the sixth lens (L6).

The distance from the focal point of the main lens system to the first surface of the rear conversion lens system is expressed as do.

(Leaving space below) Example 1 Enlargement magnification 2.0 do=43.5 f=-80,1FNO,=4.0 Radius of curvature Axis top surface interval Refractive index (Nd) Atsube number (νΣd=28.923 f f=- 144,1 f■=-192,2 fμr H=0.75, R/R=-0,1111-
11T-2 RI -2-2" ■-2-3=1.22shi3-shi,=
6.77 Example 2 Enlargement magnification 2,0 do=43.5 f=-73,5F NO,=4.0d)
Radius of curvature Axis surface spacing Refractive index (Ncl) Atsube number (νd) Σd=29.826 ” I −2-21-2-3=1・28/R shi, −shi, = 6.77 11-Example 3 Enlargement magnification 2,0 do=43.5 f=-70,5FNO0=4.0 Radius of curvature Axis top surface interval Refractive index (N, () Atsbe number (zdΣd = 30.050 f, =-140,3" I - 2-2/RI -2-3=1・18ν, -shi,=8.80

[Brief explanation of the drawing]

Figures 1, 2, and 3 show Example 1゜2.3, respectively.
FIG. 4, FIG. 5, and FIG. 6 are aberration curve diagrams of Examples 1 and 2.3, respectively. Applicant Minolta Camera Co., Ltd. Figure 1 Figure 2 Figure 1 Procedural amendment April 3, 1988 1, Case description 1988 Patent Application No. 35186 2 Name of invention Telephoto rear conversion lens system 3, Correction Applicant Address 2-30 Azuchi-cho, Higashi-ku, Osaka Osaka Kokusai Building Name (607) Minolta Camera Co., Ltd. Voluntary Amendment 5, Subject of Amendment (1) "Detailed Description of the Invention" in the Specification Column 6, Contents of amendment (1) The "Claims" of the specification will be amended as shown in the attached sheet. (2) Page 7, line 8 to line 1o, "It becomes... again. j is deleted. Applicant: Minolta Camera Co., Ltd. Appendix Amended Claims (1) Both are negative composite refraction It consists of a front group and a rear group that have high power, and the front group consists of a negative lens with a strongly concave surface facing the image side in order from the object side, and a biconvex lens arranged on the image side.
component, and a second component consisting of a biconcave lens and a positive lens disposed on the image side thereof, and the rear group includes a negative lens with a strongly concave surface facing the object side, and a biconvex lens disposed on the image side thereof. A rear conversion lens system for telephoto use, consisting of six lenses as a whole, and characterized by satisfying the following conditional expression: 0.74<f I/f ■<2.5 -0.2 <R/RII-1<0 11-1 ]1-2 /R 1,00<01.00<RI-2,,,-3<1.2
90.10<D/RII-1<0.20l-1 nl>1.8 ν, -ν, >5.00 However, f I: combined refractive power of the front group, f: combined refractive power of the rear group, ■ R: Half radius of curvature of the object side of the negative lens in the rear group [-1 radius, R: Radius of curvature of the image side of the negative lens in the rear group [-2 Ri-2-2' of the second component of the front group Radius of curvature of the negative lens (L3) on the image plane side J-2-3' Radius of curvature of the object of the positive lens (L4) in the second component of the front group: Air distance between the front and rear groups n1: Front group second component Refractive index νi of one-component negative lens (L, ): number of the i-th lens. (2) The telephoto rear conversion lens system according to claim 1, wherein the negative lens of the first component and the biconvex lens are bonded together. -2~ Procedural Amendment Written by the Commissioner of the Japan Patent Office Yoshi 1) Kyoto Moon 1. Indication of the case 1988 Patent Application No. 35186 2. Name of the invention Telephoto Rear Fever Noyon Lens System 3. Person making the amendment Related Applicant address 2-30 Azuchi-cho, Higashi-ku, Osaka City Osaka Kokusai Building name (607) Minolta Camera Co., Ltd. Showa 6
June 16, 1983 (Shipping date: July 19, 1988) 5, Amendment to procedures subject to amendment 4q 8, 1988

Claims (2)

[Claims] (1) Consisting of a front group and a rear group, both of which have a negative composite refractive power, the front group includes a negative lens with a strongly concave surface directed from the object side to the image side, and a biconvex lens arranged on the image side. The first consisting of
component, and a second component consisting of a biconcave lens and a positive lens disposed on the image side thereof, and the rear group includes a negative lens with a strongly concave surface facing the object side, and a biconvex lens disposed on the image side thereof. A telephoto rear conversion lens system is comprised of six lenses as a whole and is characterized by satisfying the following conditional expression: 0.74<f_I /f_II<2.5 -0.2<R_II_-_1/R_II_-_2<01.0
0<R_ I _−_2_-_2/R_ I _−_2_-_
3<1.290.10<D/R_II_-_1<0.20 n_1>1.8 ν_3-ν_1>5.00 However, f_ I: Combined refractive power of the front group, f_II: Combined refractive power of the rear group, R_II_-_1: Radius of curvature of the object side of the negative lens in the rear group, R_II_-_2: Radius of curvature of the image side of the negative lens in the rear group R_ I _-_2_-_2: Negative lens in the second component of the front group Radius of curvature on the image plane side of (L_3) R_ I _-_2_-_3: Radius of curvature D of the object of the positive lens (L_4) in the second component of the front group: Air distance between the front and rear groups n_1: The first component of the front group Refractive power νi of one-component negative lens (L_1): Abbe number of the i-th lens. (2) The telephoto rear conversion lens system according to claim 1, wherein the negative lens of the first component and the biconvex lens are bonded together.