JPS5965821A - Telephoto lens system - Google Patents

Abstract

PURPOSE:To obtain a lens system which provides good depiction performance from infinity to the shortest distance and is small in size by incorporating a negative lens in the 1st group and satisfying specific conditional equation. CONSTITUTION:A telephoto lens system contains a negative lens in the 1st group and is so constituted as to satisfy the conditional equation 1.5f<fI II<2.1f while the lens is focused to infinity wherein the focal length of the entire system and the combined focal length of the 1st, 2nd groups I , II are designated respectively as f, fI II. The small-sized lens system which provides good depiction performance from infinity to the shortest distance is thus obtd. according to such constitution.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement of a focus song method in a telephoto lens system. Generally, photographic lenses focus on the subject by moving the entire lens system, but in order to improve operability, lenses that allow focusing by only moving a part of the lens system have been developed to improve operability. The system is known 1. The present invention consists of 31 strokes, in order from the object side: a positive Nth stroke (f), a negative second group (II), and a positive third group (III). The purpose of this telephoto lens is to provide a compact lens system that has good depiction performance from infinity to the closest distance in a telephoto lens that focuses by moving only the second group (b). .

In other words, the feature is that the first group includes a negative lens, and when the lens is focused at infinity,
The focal length of the entire system, and the first and second g1(f), (II
>, respectively, when the composite focal lengths of
．． The goal is to satisfy f.

Next, the conditions listed in - will be explained. The present invention is directed to the soup Y
The above negative lens included in (1) and the negative 21st (11)
The 1st fff (1
, ) and the 20th (1 m) composite focal length within a predetermined range, and the requirements for this are the condition (1) in item 2. When the lower limit of condition (1) is approached, the total length of the lens increases, and if the telephoto ratio is kept constant, the bank focus becomes short, making it difficult to attach it to an eye reflex camera. Therefore, it is necessary not to divide the lower limit value. On the other hand, Koushichi, who is approaching the 2nd limit, is on the 31st stroke (III
) means that the refractive power becomes stronger, which misses the objective of reducing the telephoto ratio. Therefore, it is necessary not to exceed the two limit values.

In carrying out the present invention, it is advantageous to satisfy the condition tl and at the same time follow the sequence of steps described below. In other words, the 17th ff (I) includes, in order from the object side, the positive lunzu (L, ), the second positive meniscus convex toward the object side,
Lens (L2), consisting of positive and negative cemented lenses, cemented 1h
J is composed of a meniscus-shaped negative third lens (L3) with a convex surface facing the object side, and the second R1! (11) is
1 negative 'o) Junction 1y 7 S' (L4+, The 13th group is an array consisting of at least one positive lens (L-, ).The 1st group (I) is arranged in order from the object side. Positive first and second lenses (Ll) (L2), negative third lenses (
L3\ and a meniscus-shaped negative fourth lens (+-S) with the convex surface facing the object side.

Furthermore, in any case, good results can be obtained if the following conditions are followed.

However, 'l+'2 is the spacing between the first punch and the second group, and the spacing between the 21st punch and the third group when the focus is set at infinity.

Condition (2) determines the position of the first lun group.

When the lower limit is exceeded, the second group comes close to the first group, so there is no suitable aperture position, and the interaction with the off-axis light beam becomes worse. On the other hand, if the upper limit is exceeded, it becomes difficult to correct the positive distortion generated in the first lens group, and it is also difficult to ensure the amount of movement of the second lens group, which is undesirable as it leads to an increase in the size of the system. In any case, if the aberration is outside this range, aberration fluctuations due to focusing become unacceptable.

Next, examples of the present invention will be shown.

Example 1 f = 1t) OFno, = 2.8 2ω = 1.8° Radius of curvature Core thickness Refractive index AS nove number flll =
1. s77 Example 2 f =100 F no, =4. ．． 0 2
ω=12.5° radius of curvature Core thickness Refractive power Ambe number 02 01b / JI+-1,83f Example 3 7=100 Fno, = 2.8 2ω=18° Radius of curvature Core thickness Refractive power Abe number 1.7 ．． =≠
Item # □- 1. In addition, the following conditions (
It is advantageous to follow 3), but it is advantageous to follow the first-order condition f4) (5) when the ψ·3 lens is used as a cemented lens.

(3+ 0.15<D/Σd<(1,4(4)
15 < (va-νb) < 38(51(ra-d
a)<rb<f However, 1): 1st group (image 11 from the object side end (rl) of Il
11 The axial distance at the (r7) dimension of the end Σd: The axial distance of the entire system Shea, Shib: Sotl-The object of the third lens (L3) of the first group (■) 1till lens and the Atsube number of the image side lens, 1'a + rb', its power 2, the first group (1
The radius of curvature of the object side surface and cemented surface of the third lens (L3) in 1, da: the object (14111/on the axis of the lens) of the third lens (L3) in (1); Thickness f: Focal length of the entire system at infinity.Next, we will add an explanation about the first condition above.Condition (3) exists.If the F-limit lens is damaged, the back focus will be 1%,
A tendency occurs, and the distance from the image plane to the tip of the lens becomes longer, moving away from compactness. Below the limit value;・
If? If the total length of the lens is made compact by shortening 1 m D, the refractive force of each lens will become stronger, and spherical [-H1 aberration and coma aberration will worsen. On the other hand, if the upper limit is exceeded, the cemented third lens (L3) or the single lens σ) third lens (L,
) and the fourth lens (L12), the incident height of the axial (principal) Y-ray that passes through it becomes lower, the achromatic effect decreases, and the elimination of the chemical aberration becomes better.

Conditions (41i-j: , This is to satisfactorily correct on-axis and off-axis chromatic aberrations while maintaining parallax alignment with the movable J lens group (1r). When the lower limit is exceeded, the effect of chromatic aberration decreases. , chromatic aberration, spherical aberration, and comatic aberration, and it is difficult to obtain a high-contrast depiction.'' If the second limit (I) is exceeded, the color uniformity is considered to be good, but the third lens of the cemented L
3) O condition (
5) defines the shape of the cemented surface (r6) of the third cemented lens (L3), and by setting condition (4) k14, it is made to have an appropriate positive refraction chip for the subwavelength. [If the limit is exceeded, the influence on the sub-wavelengths will be excessive, and the balance of east 11-L and off-axis chromatic aberration will be disrupted.
1 Ru. If the upper limit is increased by 1 g, the correction effect will be lost and the depiction quality will deteriorate due to chromatic aberration.

[Brief explanation of drawings]

Figure 1.4.7 shows the lens cross section of Examples 1 to 3.
, Figure 2.5.8-1 Aberration curve diagram when the subject is at infinity with the lens systems of Examples 1 to 3, No. 3.6, 9171
N is an aberration curve diagram when close-up photography is performed at a magnification of β-1/10 by moving the second group using the lens systems of Examples 1 to 3. ■・Group 1 1 [Group 2 JIT/Group 3 Applicant Minolta Camera Co., Ltd.

Claims (1)

[Claims] 1. In order from the object side, a positive first group, a negative second group, and a positive third group.
A telephoto lens system consisting of a group of 3 m and focusing by moving only the second group, which includes a negative lens in the first group and satisfies the following conditional expression: 15f full, <21. / However, l: focal length of the entire system when focused on an object at infinity, and j□: combined focal length of the first and second groups when focused on an object at infinity. 2. The first group consists of an iE lens, a positive meniscus second lens convex to the object side, and a positive and negative cemented lens, with the cemented surface facing the object side in order from the object side. Claim 1, characterized in that the second group consists of a negative meniscus-shaped negative third lens, the second group consists of a positive and negative cemented lens, and the third group consists of at least one positive lens. Telephoto lens system listed. 6. The first group consists of, in order from the object side, a positive first lens, a negative third lens, and a fourth lens, which is a negative meniscus with its convex surface facing the object side. 2. The telephoto lens system according to claim 1, wherein the second group includes a positive and negative cemented lens, and the third group includes at least one positive lens.