JPS5841488B2 - attachment lens - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an attachment lens for the purpose of enlarging the focal length of a photographic lens having a fixed focal length.

As such an attachment lens, there is an attachment lens which is arranged on the image side of the photographic lens to which this actuator is attached, since it has the advantage of being miniaturized.

When an attachment lens is placed on the image side of the photographic lens, the imaging magnification of the attachment lens is β, and the focal length of the attachment lens is f.

, the distance from the front principal point of the attachment lens to the focal position of the photographic lens is 81 photographic lens and actunamen 1-
When the focal length of the f1 photographic lens is fM, the combined focal length with L.lens has the relationship expressed by the following equations.

As can be seen from this relationship, β>1 and S>0, so fo becomes O, and when β is given, f.

is determined by S, and fo is a negative and small value.

Therefore, the Petzval sum becomes a large negative value and the field curvature worsens.

Therefore, we improved the Petzval sum by changing the value of S,
As an example of a lens system that prevents deterioration of field curvature, there is an attachment lens that has a negative front group and a positive rear group, such as the lens system described in Japanese Patent Publication No. 12421. It is being

However, when the front group is made negative and the rear group is made positive in this way, the first
As can be seen from the graph of the astigmatism of the lens system of Example 1 of the Japanese Patent Publication No. 51-12421 shown in FIG. 3A, the state of the astigmatism cannot be said to be sufficiently good.

(Note that the curve in Fig. 13A is for the actunament lens only.) The present invention was made in view of the above points, and is an actunament lens placed at the rear of the photographic lens. The objective of the present invention is to provide an attachment lens in which both groups are configured to have negative power, and various aberrations such as field curvature and astigmatism are well corrected.

In a negative lens system consisting of two lenses, the following relational expression holds when considering a lens system consisting of two concave lenses and a lens system consisting of a concave lens and a convex lens.

However, F is the focal length of the entire system, F is the focal length of the front group, and Fn is the focal length of the front group and the rear group, respectively.

Further, assuming that the refractive index of the front group is n□ and the refractive index of the rear group is n■, the Petzval sum of the lens system is expressed by the following equation.

From these formulas (d) and (e), F y dt n(p n
, iI are each constant, the Petzval sum can be made smaller when F□ and FII each take a negative value than when F□ and F■ have opposite signs.

The attachment lens of the present invention has a negative refractive power for both the front group and the rear group, and the front group includes a negative meniscus first group lens with a convex surface facing the object side, and a meniscus lens group with a convex surface facing the object side. The second group lens is a cemented negative lens, the third group is a positive lens, and the rear group is a fourth group lens, which is a positive meniscus lens with a convex surface facing the image side, and the fifth group lens is a negative lens. It becomes more.

The attachment lens of the present invention having these lens configurations is characterized by satisfying the following conditions.

However, f.

is the focal length of the entire attachment lens system, f□ is the composite focal length of the first to third group lenses, that is, the front group, fI
Il is the composite focal length of the fourth group lens and the fifth group lens, that is, the rear group, and d7 is the air distance between the third group lens and the fourth group lens, that is, between the front group and the rear group.

These conditions (1) and (2) are conditions for reducing the curvature of field and also reducing the spherical aberration and coma aberration while the master lens and the attachment lens do not mechanically interfere with each other.

If either f□ or fII becomes positive under condition (1) among these conditions, the Petzval sum deteriorates and the field curvature becomes a dog, as described above.

Also, in condition (2), if d7 is smaller than the upper limit, comatic aberration worsens, and if it is smaller than the lower limit, the Petzval sum worsens, the curvature of field increases, and spherical aberration worsens.

The above conditions indicate the basic configuration of the present invention described above, and are based on ideas that have not been adopted in conventional attachment lenses. A lens system to which the following conditions are attached is an even better lens system.

However, r2. r is the radius of curvature of the image-side surface of the first group lens and the image-side surface of the fourth group lens, and n2, n3, pn5 are the refractive indices of both lenses of the second group lens and of the fourth group lens, respectively.

Among these articles f'443) to condition (6), condition (3)
), in condition (4), r2/ l fol , r
When g/I f61 falls below the upper limit, the Petzval sum deteriorates, and the curvature of field becomes too large, causing spherical aberration to worsen.When g/I f61 falls below the upper limit, the chromatic aberration of magnification worsens.

Article f! 4: In (6), when n5 becomes a dog than the upper limit,
Spherical aberration worsens.

In condition (5), when n2-n3 becomes smaller than the lower limit, the chromatic aberration of magnification worsens and the curvature of field becomes dog.

If the following conditions (7) to (10) are satisfied in addition to the above conditions (1) to (6), an even more excellent attachment lens can be obtained.

However, r5 p and r6 are the image side surface of the third group lens, respectively,
The radius of curvature of the object side surface of the fourth group lens, n3 is the refractive index of the image side lens of the second group lens, and s2. C3 is the Abbe number of both lenses of the second lens group.

Among the above conditions, when r6/I fo + becomes more than the upper limit in condition (8), the chromatic aberration of magnification worsens, and when it becomes smaller than the lower limit, the Petzval sum deteriorates and the field curvature becomes a dog.

In condition (7), when r,/I fol is smaller than the upper limit, the distortion becomes larger, and when it becomes smaller than the lower limit, the spherical aberration worsens.

If 03 is smaller than the lower limit in condition (9), the chromatic aberration of magnification worsens and the curvature of field becomes dog.

When C3-C2 becomes smaller than the lower limit under condition (10), chromatic aberration of magnification worsens.

Examples of the attachment lens of the present invention described above are shown below.

However, f is the composite focal length when the attachment lens of each example is added to the photographic lens having the data described later, F is the brightness when the attachment lens is also attached to the photographic lens, and ω is the resultant value for the same case. angle of view,
fB is the back focus in the same case, fo is the focal length of the attachment lens, do is the distance from the final photographic lens to the attachment lens, rl, r2 ・
... C7 Radius of curvature of each surface of the tactile lens, dl, d
2... is the thickness and lens spacing of each lens of the attachment lens, nl y R2... is the refractive index of each lens of the attachment lens, and SI1. C2... is the Atsube number of each attachment lens.

An example of a photographic lens to which this attachment lens is added is shown in FIG. 12 and has the following data.

However, f~), P[), t'B~), and ω~) are the focal length, brightness, and back focus of this photographic lens, respectively.

The angle of view is R,, R2, .

R8 is the radius of curvature of each surface, DI p R2p...R8
is the radius of curvature of each surface, D□, R2, . . . R9 is the thickness and lens spacing of each lens, N, , N2. ...N5 is the refractive index of each lens, ■1. v2...v5 are the Atsube numbers of each lens.

The overall aberration curves when added to the photographic lens of each of the above embodiments are shown in FIGS. 2 to 11, respectively.

Moreover, FIG. 13 B1 shows the state of astigmatism of only the attachment lens of Example 1 of the present invention, as described in the above-mentioned Japanese Patent Publication No. 51-124.
This is a side-by-side illustration of the astigmatism of Example 1 of the lens system in Publication No. 21 (FIG. 13A).

Furthermore, the Petzval sums of only the attachment lens of Example 1 of Japanese Patent Publication No. 51-12421 and the attachment lens of the present invention are -0,0059 and -0,
It is 0017.

From these facts, it can be seen that the attachment lens of the present invention is better than the conventional one.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of the attachment lens of the present invention, and FIGS. 2 to 11 are aberration curve diagrams when the lens systems of Examples 1 to 10 of the present invention are added to photographic lenses, respectively.
FIG. 12 is a sectional view of an example of a photographic lens to which an attachment lens of the present invention is added, and FIG. 13 is a diagram showing the state of astigmatism in the conventional example and the first embodiment of the present invention.

Claims (1)

[Claims] 1. A first negative meniscus lens with a convex surface facing the object side.
a group lens, a second group lens that is a cemented negative meniscus lens with a convex surface facing the object side, a third group lens that is a positive lens, and a fourth group lens that is a positive meniscus lens that has a convex surface facing the image side. An attachment lens is characterized in that it is a lens composed of 6 elements in 5 groups, including a 5th group lens which is a negative lens, and satisfies the following conditions. \-/ l/, JL \u'/ / l
LOl ++ty-&but f. is the focal length of the entire system, fI is the combined focal length of the 1st group lens, 2nd group lens, and 3rd group lens, f■ is the combined focal length of the Showa 4th group lens and 5th group lens, d7 is the 3rd group lens This is the air distance between the lens and the fourth group lens. 2. The first negative meniscus lens with the convex surface facing the object side.
a group lens, a second group lens that is a cemented negative meniscus lens with a convex surface facing the object side, a third group lens that is a positive lens, and a fourth group lens that is a positive meniscus lens that has a convex surface facing the image side. An attachment lens characterized in that it has a configuration of six lenses in five groups, including a negative fifth lens group, and satisfies the following conditions. However, f. is the focal length of the entire system, f□ is the combined focal length from the 1st group lens to the 3rd group lens, fI is the combined focal length of the 4th group lens and 5th group lens, r2 p r9 are the respective 1st group lenses The radius of curvature of the image-side surface of and the image-side surface of the fourth group lens,
d7 is the air distance between the third group lens and the fourth group lens, n
2jn3jn are both lenses of the second group lens and the fourth lens group, respectively.
This is the refractive index of the group lens. 3. The first negative meniscus lens with the convex surface facing the object side.
a group lens, a second group lens that is a meniscus cemented negative lens with a convex surface facing the object side, and a third group lens that is a positive lens;
An attachment lens comprising six lenses in five groups, including a fourth group of positive meniscus lenses with a convex surface facing the image side and a fifth group of negative lenses, and satisfying the following conditions. However, f. is the focal length of the entire system, f■ is the combined focal length from the first group lens to the third group lens, f□ is the combined focal length of the fourth group lens and the fifth group lens, r2゜r5 p r6 p r9
are the radii of curvature of the image-side surface of the first group lens, the image-side surface of the second group lens, the object-side surface of the third group lens, and the image-side surface of the fourth group lens, respectively, and d7 is the radius of curvature of the image-side surface of the fourth group lens. The air distance between the lens and the fourth group lens, ``2.n3, n5 are the refractive indexes of both lenses of the second group lens and the fourth group lens, respectively, and C2.C3 are the refractive indexes of both lenses of the second group lens, respectively. is Atsbe's number.