JP2526144B2 - Copy zoom lens - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a zoom lens for copying, which is used in a copying machine or the like and which has a wide F / # and is capable of wide zooming and has a constant conjugate length even during zooming. is there.

[Conventional technology]

In recent years, it has become common for copying machines to be capable of continuous zooming instead of stepwise zooming. Therefore, as a copying lens, zooming is performed while moving a part of the lens. A lens system that does Then, with the advancement of technology, it is desired to vary the magnification over a wide range of about 0.5 to 2.0 at the time of varying the magnification, and the optical path length from the object plane to the image plane, that is, the conjugate length is constant. It is necessary to change the magnification while keeping it in order to simplify the mechanism.

Further, colorization has been widely adopted, and therefore, a lens having a bright F number is demanded.

[Problems to be Solved by the Invention]

However, a zoom lens that has a constant conjugate length during zooming and has a zooming range of about 0.5 to 2 times has a limit in terms of brightness and compactness.

The present invention has been made to solve such a problem, in which the conjugate length is constant at the time of zooming, and the conjugate length is from 0.5 times as low to 2 times.
It is an object of the present invention to provide a compact copying lens which is capable of zooming up to about twice as high, has an F-number of 5.1 or more, and is compact.

[Means for solving the problem]

In order to achieve the above object, the present invention has, in order from the object side, a first lens group I of negative power composed of a positive meniscus lens having a convex surface facing the object side and a biconcave lens, and an image forming side. A second lens group II of positive power consisting of a negative lens with a strong concave surface and a biconvex lens, and a third lens group of positive power consisting of a biconvex lens and a negative lens with a strong concave surface facing the object side. III, a biconcave lens and a positive meniscus lens having a convex surface facing the image side
In a copying zoom lens including the lens group IV, d _{I, II} : a distance between the first lens group I and the second lens group II d _{II, III} : a distance between the second lens group II and the third lens group III d _{III, IV} : Distance between the third lens group III and the fourth lens group IV f _II : Focal length of the second lens group II f _III : Focal length of the third lens group III f _1.0 : Whole system at equal magnification (1) 0.55 <f _II / f _1.0 <0.95 (2) 0.55 <f _III / f _1.0 <0.95 (3) d _{I, II} + d _{II, III} + d _{III, IV} = constant While satisfying each condition, the second lens group II and the third lens group III are moved with respect to the first lens group I and the fourth lens group IV, and the first lens group I to the fourth lens group IV
By moving the entire lens up to the optical axis direction,
The zoom lens for copying is characterized in that it is possible to continuously change the magnification while keeping the conjugate length from the object plane to the image plane constant.

[Action]

As shown in FIGS. 1 and 2, at the same magnification (M = 1.0X), the second lens group II and the third lens group III are disposed between the first lens group I and the fourth lens group IV. And are arranged almost symmetrically. At the time of zooming (M> 1.0X, M <1.0X), the entire lens from the first lens group I to the fourth lens group IV moves, and at the same time the first lens group I and the second lens group II Distance, distance between second lens group II and third lens group III, third distance
The distance between the lens group III and the fourth lens group IV is changed to change the magnification, and the conjugate length and aberration are corrected at the time of changing the magnification. At the time of enlargement (M> 1.0X) and reduction (M <1.0X), the distance d between the first lens group I and the second lens group II
_{I, II} and the distance d _{III, IV} between the third lens group III and the fourth lens group IV increase, and the second lens group II and the third lens group III
And the distance d _{II, III} between and decreases.

The diaphragm is, for example, the first lens group I to the fourth lens group IV.
But with the second lens group II always.
And the third lens group III.

In order to realize a high performance and compact lens, it is necessary to satisfy the conditions (1) and (2).

(1) 0.55 <f _II / f _1.0 <0.95 (2) 0.55 <f _III / f _1.0 <0.95 This conditional expression is the second lens group I for the focal length of the entire system.
I, the focal length of the third lens group III are defined.

If the upper limits of the conditions (1) and (2) are exceeded, the powers of the second lens group II and the third lens group III necessary for zooming become loose, so the amount of movement of the lens groups accompanying zooming increases and the compact size. When the lower limit is exceeded, the compactness is satisfied, but the fluctuation of the image plane due to zooming cannot be completely corrected.

Further, it is necessary to satisfy the condition (3) in order to keep the total length constant during zooming.

(3) dI _{, II} + dII _{, III} + dIII _{, IV} = constant By satisfying this condition, the lens moving mechanism becomes compact and the production can be performed at low cost.

Further, in order to satisfactorily correct the axial chromatic aberration and the spherical aberration over the entire zoom range, the following condition (4),
It is desirable to satisfy (5) and (6).

(5) 0.26 <r _s / f _1.0 <0.40 (6) 0.26 <−r _e / f _1.0 <0.40 Condition (4) is that the first lens has an Abbe number ν ₁ and the second lens has an Abbe number ν _2. , The seventh lens's Abbé number is ν ₇ ,
It defines the dispersion of the convex lens and the concave lens in the first lens group I and the fourth lens group IV when the Abbé number of the eighth lens is ν _8, and if the upper limit of this condition (4) is exceeded, the magnification change will occur. It becomes impossible to correct the fluctuation of axial chromatic aberration at the time,
If the value goes below the lower limit, axial chromatic aberration itself cannot be completely corrected.

The condition (5) defines the radius of curvature r _s of the first lens surface when counted from the object side, and the condition (6) defines the radius of curvature r _e of the final lens surface when counted from the object side. When the upper limits of these conditions are exceeded, the spherical aberration during zooming becomes excessive, and when the lower limit is exceeded, the spherical aberration during zooming becomes under, and correction becomes difficult.

〔Example〕

Hereinafter, each embodiment of the present invention will be described in detail based on the basic lens configuration shown in FIG.

However, in the following description, m: surface number sequentially counted from the object side r _i : radius of curvature of the i-th lens surface counted from the object side d _i : thickness of the i-th lens component counted from the object side Or air spacing n _i : Refractive index of the i-th lens component from the object side with respect to d-line ν _i : Abbe number of the i-th lens component counted from the object side θ: Half angle of view r of copying lens _s : The radius of curvature of the first lens surface counting from the object side _re : The radius of curvature of the last lens surface counting from the object side.

The first embodiment is based on the basic lens configuration shown in FIG. 2. The first lens group I having negative power in order from the object side is a positive meniscus lens L ₁ having a convex surface directed toward the object side.
And is biconcave lens L ₂ Prefecture, positive second lens group II of the power is biconcave lens L ₃ and a biconvex lens L ₄ Metropolitan with a strong concave surface facing the image side, the third lens of positive power Group II
I is composed of a biconvex lens L ₅ and a biconcave lens L ₆ with a strong concave surface facing the object side, and the first lens group IV of negative power is a biconcave lens L ₇ and a positive meniscus convex surface facing the imaging side. It consists of a lens L ₈ . The specific structure is shown in the table below.

The aberration curve according to this specific configuration is as shown in FIG.

The second embodiment is based on the basic lens configuration shown in FIG. 2, and its specific configuration is as shown in the table below.

The aberration curve according to this specific configuration is as shown in FIG.

The third embodiment is based on the basic lens configuration shown in FIG. 2, and the first lens unit I having negative power in order from the object side is a positive meniscus lens L having a convex surface facing the object side. The second lens group II having a positive power is composed of ₁ and a biconcave lens L _2, and the biconcave lens has a strong concave surface facing the image forming side.
The third lens group III, which is composed of a cemented lens L ₃ + L ₄ with L ₃ and a biconvex lens L ₄ , and has a positive power, cements a biconvex lens L ₅ with a biconcave lens L ₆ with a strong concave surface facing the object side. Lens L ₅
+ L ₆ is composed of, the fourth lens group IV of the negative power positive meniscus lens having a convex surface directed toward the biconcave lens L ₇ and the image-forming side
It consists of L ₈ and. The specific structure is shown in the table below.

The aberration curve according to this specific structure is as shown in FIG.

Various aberrations such as spherical aberration in FIGS. 3, 4 and 5 which are aberration curve diagrams of the first, second and third examples are well corrected.

〔The invention's effect〕

As is clear from the above description, according to the present invention, since the lens configuration and each condition are satisfied, the conjugate length is kept constant during zooming, and the brightness is F5.1 or higher, and It is now possible to provide a compact zoom lens for copying, in which the aberration does not deteriorate even when zooming over a wide range of about 0.5 to 2 and the total lens length is constant.

[Brief description of drawings]

FIG. 1 is an explanatory view showing a lens movement mode of a zoom lens for copying according to the present invention at the time of zooming, FIG. 2 is a lens block diagram of a basic configuration at the time of equal magnification and zooming, and FIG. FIG. 4 is an aberration curve diagram of Example 1, FIG. 4 is an aberration curve diagram of Example 2, and FIG. 5 is an aberration curve diagram of Example 3. I to IV: First lens group to fourth lens group L ₁ to L ₈ : First lens to 8th lens X: Optical axes r ₁ , r ₂ , ... R ₁₆ : Radius of curvature d ₁ of each lens surface , d _2, ··· d _15: thickness or air space of the lens

Claims (1)

(57) [Claims] 1. A first lens group I of negative power composed of a positive meniscus lens having a convex surface facing the object side and a biconcave lens in order from the object side, and a negative lens having a strong concave surface facing the imaging side. A second lens group of positive power consisting of a biconvex lens and
II, a third lens group III of positive power consisting of a biconvex lens and a negative lens with a strong concave surface facing the object side, a biconcave lens and a positive meniscus lens with a convex surface facing the image side A zoom lens for duplication consisting of a fourth lens group IV of the following power: d _{I, II} : distance between the first lens group I and the second lens group II d _{II, III} : second lens group II and third lens Distance from group III d _{III, IV} : Distance between third lens group III and fourth lens group IV f _II : Focal length of second lens group II f _III : Focal length of third lens group III f _1.0 : etc. Assuming the combined focal length of the entire system at the time of doubling, (1) 0.55 <f _II / f _1.0 <0.95 (2) 0.55 <f _III / f _1.0 <0.95 (3) d _{I, II} + d _{II, III} + d _{III ,} while satisfying _IV = constant becomes each condition, the second lens group II and the third lens group III first lens group I, is moved relative to the fourth lens group IV The first lens group I to the fourth lens group IV
By moving the entire lens up to the optical axis direction,
A zoom lens for copying, which is capable of continuously varying the magnification while keeping the conjugate length from the object plane to the image plane constant.