JPH064332Y2 - Lens system with auxiliary lens - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a lens system equipped with an auxiliary lens that changes the focal length of the entire system by attaching and removing the auxiliary lens between the main lens and the film surface, and in particular, a short-distance object when the auxiliary lens is attached. The present invention relates to a lens system provided with an auxiliary lens having a characteristic of focusing on a lens.

Conventionally, it is generally known that a converter lens is mounted on the object side or image side of a photographic lens, and the focal length of the photographic lens is expanded or reduced while the position of the focal plane of the photographic lens is held constant. . In this case, in the front converter lens system mounted on the object side of the photographic lens, the size of the converter lens, particularly the diameter of the front lens, becomes large, and it is difficult to downsize the lens system. In contrast,
The rear converter lens system in which the converter lens is arranged on the image field side of the photographic lens is more advantageous in reducing the lens diameter than the front converter lens system.

As an example of taking advantage of this kind of advantage, the present applicant is
-46244 proposes to reduce the number of constituent lenses of the converter lens to reduce the storage space when this converter lens is stored, and to reduce the size of the camera body.

Also, considering a focusing system for a short-distance object when an auxiliary lens is attached between the main lens and the film surface, in a lens system in which an aperture mechanism or a shutter mechanism is arranged between the main lens and the auxiliary lens, The so-called total focus method, in which the main lens, the auxiliary lens, the diaphragm mechanism, the shutter mechanism, etc. are moved integrally, complicates the mechanical structure. In general, a partial focusing method such as a front lens group focusing only the main lens toward the object side and a rear lens group focusing only the auxiliary lens toward the film surface side is adopted.

However, the partial focusing method has a photographing magnification β = −
Since a considerable amount of lens movement is required for a short-distance object of about 0.2 or more, as a result, the amount of peripheral light is significantly reduced. Therefore, in a lens system having a small lens outer diameter for the purpose of downsizing the lens system, the object distance at which close-up photography is possible is limited due to a reduction in peripheral light amount.

The purpose of the present invention is to attach and detach an auxiliary lens between the main lens and the film surface to change the focal length of the entire system.
Another object of the present invention is to provide a lens system including an auxiliary lens capable of enlarging the object distance at which close-up photography is possible when the auxiliary lens is attached.

In order to achieve the above object, in the present invention, as focusing when an auxiliary lens is attached, focusing is performed by moving the main lens toward the object side up to an object at a certain short distance, and further, the photographing magnification. Is 0.1
Focusing is performed by moving the auxiliary lens for an object at a short distance including 5 times. Further, in particular, the auxiliary lens itself is arranged adjacent to the diaphragm, so that the auxiliary lens itself is downsized.

By adopting such a focusing method, it is possible to obtain a lens system having good performance over a wide shooting distance, and it is possible to reduce a decrease in light amount around the screen. In particular, if an auxiliary lens is incorporated on the film surface side, unnecessary space is unnecessary and it is preferable for aberration correction.

Further, in the present invention, it is preferable that the auxiliary lens is mounted between the main lens and the image plane at the same time when the main lens is moved to the object side. In this way, the wasted space of the lens system is reduced, which is advantageous for downsizing the lens system.

More preferably, it is preferable that the auxiliary lens is composed of the first positive lens, the second negative lens, and the third positive lens in order from the object side for good aberration correction. When the auxiliary lens is constructed by using the positive and negative lenses in this way, even if the focus is adjusted to a short-distance object, the aberration can be favorably corrected over a wide object distance.

In the present invention, focusing may be performed by moving the main lens and the auxiliary lens integrally at a normal object distance.

Next, Numerical Example 1 of the main lens to which the auxiliary lens of the present invention should be attached is shown below. Ri is the radius of curvature of the lens surface, Di is the lens thickness or lens surface spacing, Ni is the refractive index of the i-th lens glass material with respect to the d-line, and νi is the Abbe number.

A numerical example 2 in which an auxiliary lens is attached to the above-mentioned main lens will be shown.

In the following examples, when mounting the auxiliary lens,
The main lens is moved to the object side so that the position of the image plane coincides with the position of the image plane when only the main lens is used.

Similarly, Numerical Example 3 of the main lens to which the auxiliary lens of the present invention should be attached and Numerical Example 4 in which the auxiliary lens is attached to the main lens of Numerical Example 3 are shown below.

FIG. 1 is a sectional view of the main lens of Numerical Embodiment 1 of the present invention, and FIG.
The figure shows various aberration diagrams for an object at infinity. First in Figure 3
FIG. 4 is a sectional view of a lens when an auxiliary lens is attached to the main lens in the figure, and FIG. 4 is a diagram showing various aberrations of an object at infinity in the lens system of FIG.

FIG. 5 is a photographing magnification β = −0.0 of the lens system shown in FIG.
FIG. 19 is a diagram of various aberrations at 75, in which focusing is performed only by the main lens and the air distance D7 is 7.53.

FIGS. 6 and 7 show a sectional view of the lens and various aberration diagrams when an object at a closer distance than the lens state of FIG. 5, β = −0.2. Focusing in this case is performed only by the auxiliary lens, and the air distances at this time are D7 = 7.53 and D8, respectively.
= 19.60.

FIG. 8 shows a sectional view of the main lens of Numerical Embodiment 3 of the present invention, and FIG. 9 shows various aberration diagrams for an object at infinity. FIG. 10 shows a lens cross-sectional view when an auxiliary lens is attached to the main lens of FIG. 8, and FIG. 11 shows various aberration diagrams for an object at infinity.

FIG. 12 shows β = −0.065 of the lens system shown in FIG.
FIG. 13 is a diagram of various aberrations at the time of, and focusing in this case is performed by only the main lens, and D7 = 8.27.

FIGS. 13 and 14 show a sectional view of the lens and various aberration diagrams when an object at a closer distance than the state of FIG. 12, β = −0.15. Focusing in this case is performed by an auxiliary lens, and the air distances at this time are D7 = 8.27 and D8 =
It is 15.0.

[Brief description of drawings]

FIGS. 1 and 2 are lens sectional views and various aberration diagrams of Numerical Embodiment 1 of the present invention, and FIGS. 3, 4, and 5 are lens sectional views and various aberrations of Numerical Embodiment 2 of the present invention. FIGS. 6, 6 and 7 show the photographing magnification β = in the numerical embodiment 2 of the present invention.
-0.2 lens cross-sectional view and various aberration charts, FIGS. 8 and 9 show lens cross-sectional view and various aberration charts of Numerical Embodiment 3 of the present invention, FIG. 10, FIG. 11 and FIG. Is Numerical Embodiment 4 of the present invention
And FIG. 13 and FIG. 14 are a lens cross-sectional view and various aberration diagrams of Numerical Embodiment 4 of the present invention when the photographing magnification .beta. =-0.15.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Yasuhisa Sato Inventor, Yasuhisa Sato, 770, Shimonoge, Takatsu-ku, Kawasaki-shi, Kanagawa Canon Inc. Tamagawa Plant (56) References JP-A-50-113228 (JP, A) JP-A-57 -46224 (JP, A) JP-A-58-129411 (JP, A) JP-B-48-32387 (JP, B1)

Claims (2)

[Scope of utility model registration request] 1. A main lens capable of photographing itself, a diaphragm located on the image plane side of the main lens, and a diaphragm mounted between the diaphragm and the image plane of the main lens for changing a focal length. ,
And in a lens system with a detachable auxiliary lens,
When the auxiliary lens is attached, focus adjustment is performed by moving only the main lens toward the object side for a subject farther than a predetermined short-distance object, and a short-distance including an imaging magnification of 0.15 times. A lens system provided with an auxiliary lens, wherein focus adjustment is performed by moving only the auxiliary lens for a subject. 2. The auxiliary lens according to claim 1, wherein the auxiliary lens comprises a first positive lens, a second negative lens and a third positive lens in order from the object side. Lens system.