JPS61138912A - Focusing system of telephoto macro-lens - Google Patents

Abstract

PURPOSE:To improve the lens performance when a lens is stopped down by moving a stop to an object side independently from the 1st lens group in the stage of focusing. CONSTITUTION:The lens constitution in the stage of the unmagnification from an infinite object is shown in (a), (b). The hatched part in the figure is an off axial luminous flux. The lens consists of the 1st lens group of a positive focal length and the 2nd lens group of the negative focal length and is disposed with the stop between both lens groups. The lens performance is not deteriorated even if the stop is stopped down when the lens is focused to the infinite object in the case of the stop fixed to the 2nd lens group but only the marginal luminous flux remains and the peripheral performance is deteriorated when the stop is stopped down by focusing the lens to the point such as unmagnification where the magnification is large. The stop is therefore made independently movable and the stop is also moved to the object side independently from the 1st lens group in the stage of extending mainly the 1st lens group to the object side and focusing the lens in the high magnification direction, by which the adverse influence of the stop to be generated in the high magnification stage is eliminated.

Description

[Detailed Description of the Invention] and i) The present invention provides a macro lens having a telephoto focal length, which can be used at all imaging magnifications from infinity to 1x, and in all conditions from wide open to closed aperture. , relates to a focusing method for a telephoto macro lens to maintain high performance.

4 Problems with Conventional Telephoto Macro Lenses During focusing, the aperture of a conventional telephoto macro lens is fixed together with the fixed lens group (rear group), and when stopped down at a point where the magnification is high, the aperture is fixed at the marginal (periphery). Only the luminous flux remains, and when the aperture is stopped, the peripheral performance deteriorates.

In a macro lens having a standard or semi-telephoto focal length, the angle of view is large, so the aperture must be included in a movable lens group (master group), and the aperture cannot be moved independently.

Also, when zooming instead of focusing,
It has long been known that the aperture moves in so-called two-group zoom lenses, or their modified versions, which consist of three or four groups and each group moves, but this movement of the aperture is due to the aperture effect (lens performance). Regardless, there are no zoom lenses whose effectiveness changes during focusing.

Purpose The purpose of the present invention is to improve the aperture effect, that is, the lens when stopped down, by taking into account the arrangement of the aperture and the movement of the aperture during focusing in a telephoto macro lens consisting of lens groups with positive and negative focal lengths. The purpose is to measure performance improvement.

From the object side, the present invention consists of a first lens group having a positive focal length and a second lens group having a negative focal length. In a telephoto macro lens that has an aperture in between and focuses mainly by moving the first lens group toward the object side, the aperture moves toward the object side independently of the first lens group during focusing. A focusing system for a telephoto macro lens characterized by the following: Furthermore, when the aperture moves as described above, it is advantageous if the aperture diameter is constant because the structure becomes simple.

An example of data of a telephoto macro lens applied to the present invention will be shown below.

■=4 f=200 ω=6.2' WD
=ω~302.2Nord
Nl too, 700 4.50 1.4
8749 70.12 214.834 0.5
0 3 56.0?9 9.96 1.49700
81.64-2002.939 0.50 5 42.778 7.32 1. /1970
0 81.66 100.598 2.82 7 18L, 169 2.8OL, 61340
43.88 31.143 12.41 9 -59.122 2.50 1.61293
37.010 -389.821 3.68
1.69680 55.511 -98.827
0.20 12 147.652 4.59 1.7340
0 51.51? , -226,5177,53~
35.05~62.58I4 -167.918 2
．． 50 1.80518 25.415 -77
．． 836 0.70 +6 -95.674 5.50 1.7130
0 53.817 54.994 39.83
18 95.940 4.30 1.5163
3 64.119 -321.938 f876.
9 However, [, ω is the focal length and half angle of view in the case of an infinite object,
IID is the distance from the object point to the first plane, fn is Banokhu y
r-cass, " is the radius of curvature of each lens surface, d is the lens thickness or lens interval, N is the d-1ine refractive index of each lens, 5, and ν is the Abbe number of each lens.

For production Figure 1 is a diagram for explaining the aperture effect (a).

(b) is a simplified lens configuration diagram for an infinite object and the same magnification. This figure shows on-axis and off-axis light rays (light fluxes), and the shaded area is the off-axis light flux.

In a telephoto macro lens consisting of a first lens group with a positive focal length and a second lens group with a negative focal length, an aperture is placed between both lens groups, but if the aperture is fixed to the second lens group, When focusing on an infinite object, there is no deterioration in lens performance even if you close down the aperture, but if you focus on an area with a large magnification such as 1x and narrow down the aperture,
Only the marginal luminous flux remains and the peripheral performance deteriorates.

Therefore, in the present invention, the diaphragm is made to be able to move independently, and when the first lens group is mainly moved or extended toward the object side for focusing in the direction of high magnification, the diaphragm is also moved independently from the first lens group. By moving the aperture toward the object side, the diaphragm's bad shadow g3 that occurs at high magnification is eliminated, and high-performance lens performance is maintained.

Effects As explained above, by adopting the focusing method of the present invention, a high-performance telephoto macro lens can be achieved at all imaging magnifications and all aperture conditions.

[Brief explanation of drawings]

FIG. 1 is a diagram for explaining the aperture effect, in which (a) is an infinite object and (b) is a simplified lens configuration diagram when the lens is at the same magnification. Patent applicant: Asahi Optical Industry Co., Ltd. Representative: Iku Matsumoto

Claims (1)

[Claims] 1. From the object side, the first lens group consists of a first lens group having a positive focal length and a second lens group having a negative focal length.
There is an aperture between the lens group and the second lens group, and the diaphragm is mainly used for the first lens group.
In a telephoto macro lens that performs focusing by moving the lens group toward the object side, the focusing of the telephoto macro lens is characterized in that the aperture moves toward the object side independently of the first lens group during focusing. Cassing method. 2. Focusing of a telephoto macro lens according to claim 1, characterized in that the diameter of the aperture remains constant when the aperture moves toward the object side independently of the first lens group during focusing. ding method.