JP2002267929A - Rear converter lens and optical equipment using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a rear converter lens which is attached to between a photographic lens and a camera main body and whose enlarging magnification is about 2, and optical equipment using the same. SOLUTION: This rear converter lens attachably/detachably attached to the image surface side of a principal lens system so as to enlarge the focal distance of an entire system and having a negative focal distance is constituted of a 1st lens group having positive refractive power, a 2nd lens group having negative refractive power, and a 3rd lens group having positive refractive power in order from an object side, and the 2nd lens group is constituted of a 21st lens whose both surfaces are concave, a 22nd lens whose both surfaces are convex and a 23rd lens turning its concave surface having strong refractive power to the object side as compared with an image surface side and having negative refractive power in order from the object side. When it is assumed that a distance on the optical axis between the 2nd lens group and the 3rd lens group is BD2, and the focal distance of the rear converter lens entire system is Ft1, they satisfy 0.09<|BD2/Ft1|<0.20.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rear converter lens which is detachably mounted behind a lens system to displace the focal length of the entire lens system to a longer one, and an optical apparatus using the same, and relates to a digital camera and a video camera. It is suitable for a camera, an electronic still camera, a camera for silver halide photography, and the like.

[0002]

2. Description of the Related Art Conventionally, in a single-lens reflex camera, a lens (rear converter lens) having a negative focal length (refracting power) is detachably mounted between an interchangeable lens (main lens system) and a camera body. It is widely practiced to increase the focal length of a lens. This method has the advantages that the focal length of the taking lens can be easily enlarged and the entire lens system can be made more compact than the type that is mounted on the object side of the taking lens. However, in this method, the open F-number increases in proportion to the magnification of the focal length of the entire system.
That is, there is a disadvantage that the brightness of the entire lens system is reduced.

[0003] Further, since many photographing lenses are usually used alone, various aberrations of only the lens system are satisfactorily corrected. However, when a rear converter lens is attached, the larger the magnification, the larger the aberration. The residual aberration of the main lens system is enlarged in proportion. For this reason, in many cases, mounting the rear converter lens on the main lens system deteriorates the image quality.

[0004] For example, when the magnification of magnification when the rear converter lens is mounted on the main lens system is 2 times, the lateral aberration is enlarged by 2 times and the image quality deteriorates.
Further, the longitudinal aberration is magnified to the square of the magnification, that is, four times. However, in the case of a rear converter lens, the F-number of the main lens system is also magnified or darkened by a factor of two. It will be magnified twice and worsen.

Therefore, in order to maintain good aberrations of the entire system when the rear converter lens is mounted on the main lens system, it is necessary to satisfactorily correct various aberrations of the rear converter lens itself.

[0006]

Since the rear converter lens has a negative refractive power and has a large negative Petzval sum by itself, when it is mounted on the main lens system, it often has a field curvature. Has the property of worsening.

In addition, when a rear converter lens is usually mounted on an interchangeable lens (main lens system), the aperture in the interchangeable lens is used because the interchangeable lens has a photographic stop.
For this reason, in the rear converter lens, the principal ray of the off-axis light flux does not cross the optical axis but passes above and below the optical axis. For this reason, there is a property that the lens form is difficult to cancel various aberrations generated by passing the light off the optical axis.

Japanese Patent Publication No. 61-13206 discloses that
We have proposed a rear converter lens which is an optical system of three groups consisting of lens groups having negative and positive refractive powers and has good performance while suppressing spherical aberration, coma aberration and the like to a small value.

[0009] However, the optical system disclosed in the publication is compact in its entirety, but a negative Petzval sum remains due to the strong refractive power of each of the constituent lens groups.

In general, when the refractive power of each lens group of the rear converter lens is increased, a predetermined magnification can be easily obtained, but the sensitivity of each lens to aberrations increases, and the manufacturing becomes difficult.

The present invention is directed to a rear converter lens which satisfactorily corrects various aberrations, in particular, satisfactorily corrects the field curvature, and always obtains high optical performance even when attached to a main lens system, and an optical system using the same. The purpose is to provide equipment.

Another object of the present invention is to provide a rear converter lens which can reduce the sensitivity of each lens group to aberration, is easy to manufacture, and can easily maintain high optical performance, and an optical apparatus using the same. And

[0013]

According to a first aspect of the present invention, there is provided a rear converter lens having a negative focal length, which is detachably mounted on the image plane side of a main lens system to increase the focal length of the entire system. The rear converter lens includes, in order from the object side, a first lens group having a positive refractive power, a second lens group having a negative refractive power, and a third lens group having a positive refractive power. Are, in order from the object side, a twenty-first lens having both concave lens surfaces, a twenty-second lens having both lens surfaces convex, and a twenty-third lens having a negative refractive power with a concave surface having a stronger refractive power directed toward the object side than the image surface side. When the distance on the optical axis between the second lens group and the third lens group is BD2, and the focal length of the entire rear converter lens system is Ftl, 0.09 <| BD2 / Ftl | <0. Satisfy 20 It is characterized.

According to a second aspect of the present invention, in the first aspect, the twenty-first lens, the twenty-second lens, and the twenty-third lens are cemented to each other.

According to a third aspect of the present invention, when the focal length of the second lens group is F2 in the first or second aspect of the present invention, 0.2 <F2 / Ftl <0.5 is satisfied. .

According to a fourth aspect of the present invention, in the first, second, or third aspect, the first lens group and the third lens group have at least one positive lens and at least one negative lens, respectively. Features.

According to a fifth aspect of the present invention, in the first aspect of the present invention, the first lens group is a meniscus lens having a negative refractive power and having a convex surface facing the object side in order from the object side. The third lens group is composed of a positive lens and a negative lens having the convex surfaces facing the image side in order from the object side.

According to a sixth aspect of the present invention, in the invention according to any one of the first to fourth aspects, the first lens group is a meniscus lens having a negative refractive power and having a convex surface facing the object side in order from the object side. The third lens group includes, in order from the object side, a meniscus lens having a positive refractive power with a convex surface facing the image side, and both lens surfaces including a negative refractive power lens having a concave surface. It is characterized by:

According to a seventh aspect of the present invention, when the focal length of the i-th lens unit is Fi in the first or second aspect of the invention, 0.6 <| F1 / Ftl | <1.0 0.2 <F2 / It is characterized by satisfying Ftl <0.51.0 <| F3 / Ftl | <2.0.

The optical system according to the invention of claim 8 is the optical system according to claims 1 to 7.
And a rear converter lens according to any one of (1) to (4).

According to a ninth aspect of the present invention, there is provided an optical apparatus including the rear converter lens according to any one of the first to seventh aspects.

[0022]

FIG. 1 is a sectional view of a main photographing lens (main lens system) when a rear converter lens according to a first numerical embodiment of the present invention is mounted on the image plane side. Although only one example is given here as the main lens system, the main photographing lens is not limited to numerical examples described later, and may be any lens system.

FIGS. 3 and 5 are lens sectional views of the rear converter lenses of Numerical Examples 2 and 3 of the present invention, respectively.

FIGS. 2, 4 and 6 show numerical examples 1, 2, and 3.
FIG. 8 is an aberration diagram when an object at infinity is imaged when the rear converter lens is mounted on a main imaging lens system.

The rear converter lens RCL includes, in order from the object side, a first lens unit L1 having a positive refractive power, a second lens unit L2 having a negative refractive power, and a third lens unit L3 having a positive refractive power at an air gap. It is composed of

Further, the second lens unit L2 includes, in order from the object side, a twenty-first lens unit having negative concave refractive power on both lens surfaces, a twenty-second lens unit convex on both lens surfaces having positive refractive power, It is composed of a 23rd lens having a negative refractive power with a stronger concave surface facing the object side than the surface side.

By making the refractive power arrangement of the entire system and the configuration in the second lens unit as described above, the rear converter lens according to the present embodiment can prevent the Petzval sum from increasing in the negative direction while suppressing the rearward increase. It is easy to easily generate the necessary negative refractive power in the entire converter lens. As a result, while the focal length of the entire system when attached to the main photographing lens is greatly enlarged (at an enlargement magnification of about 2), particularly, the deterioration of the field curvature is effectively suppressed.

Further, the second lens group and the third lens group are arranged with a relatively large air gap.

Thus, the negative refracting power of the second lens unit and the positive refracting power of the third lens unit are not extremely increased, and the negative refracting power of the entire rear converter lens system, that is, the enlargement magnification is secured and the aberration is corrected. It is easy to maintain a good balance.

Here, the air gap BD2 between the second lens group and the third lens group and the focal length Ftl of the entire rear converter lens system are 0.09 <| BD2 / Ftl | <0.20 ... (1) is satisfied.

If the lower limit of conditional expression (1) is exceeded, it is necessary to secure negative refractive power in the entire system and to increase the refractive power of each lens unit for aberration correction. for that reason,
This causes the Petzval sum to increase in the negative direction, making it difficult to correct the field curvature, which is not desirable. At the same time, the sensitivity of each lens to aberrations also increases, making it difficult to obtain stable performance in manufacturing, which is also undesirable. On the other hand, when the value exceeds the upper limit of the conditional expression (1), the total length becomes longer and the effective diameter of the third lens unit increases.

It is more preferable that the numerical range of the conditional expression (1) is 0.09 <| BD2 / Ftl | <0.14 (1a).

As described above, according to the present embodiment, a high-performance rear converter lens in which the curvature of field, which tends to increase particularly in the rear converter lens, is well corrected, and other aberrations are also well corrected is realized. it can.

The rear converter lens aimed at at the initial stage of the present invention is achieved by the above-mentioned constitution, but it is desirable to satisfy at least one of the following conditions in order to obtain higher optical performance.

The twenty-first lens, the twenty-second lens and the twenty-third lens are cemented to each other.

The rear converter lens according to the present embodiment is a more desirable embodiment by joining three lenses in the second lens group on both lens surfaces of the 22nd lens. When the three lenses in the second lens group are joined, when the light beam incident from the first lens group passes through the second lens group, strong refraction occurs on the entrance surface and the exit surface of each lens, and zigzag. Therefore, the occurrence of spherical aberration and coma aberration is reduced.

When the focal length of the second lens group is F2, the following condition is satisfied: 0.2 <F2 / Ftl <0.5 (2)

If the lower limit of conditional expression (2) is exceeded, it becomes difficult to secure a negative refracting power for obtaining a predetermined magnification in the entire rear converter lens system, and the entire optical system is undesirably enlarged. . If the upper limit of conditional expression (2) is exceeded, the Petzval sum increases in the negative direction, making it difficult to correct the curvature of field, which is not desirable.

It is more preferable that the numerical range of the conditional expression (2) is set to 0.23 <F2 / Ftl <0.4 (2a).

◎ The first lens group and the third lens group are
Each has one or more positive lenses and one or more negative lenses.

By arranging at least one positive lens and one negative lens in each of the first lens unit and the third lens unit having a positive refractive power, aberration correction in each lens unit is facilitated and high performance is achieved. A simple optical system can be easily realized.

◎ The first lens group is arranged in order from the object side.
A meniscus lens of negative refractive power with the convex surface facing the object side,
The third lens group includes, in order from the object side, a positive lens and a negative lens whose convex surfaces face the image side.

By configuring the first and third lens units in this manner, it is easy to ensure good optical performance even when the magnification is increased.

In particular, when the positive lens in the third lens group is a positive lens having a convex surface facing the image side, astigmatism can be corrected well, and a high-performance rear converter lens can be easily realized. become.

◎ The first lens group is arranged in order from the object side.
A meniscus lens of negative refractive power with the convex surface facing the object side,
The third lens group includes, in order from the object side, a meniscus lens having a positive refractive power with a convex surface facing the image side, and both lens surfaces including a negative refractive power lens having a concave surface. It is.

When the focal length of the i-th lens group is Fi, 0.6 <| F1 / Ftl | <1.0 (3) 0.2 <F2 / Ftl <0.5... · (2) 1.0 <| F3 / Ftl | <2.0 (4)

When the value exceeds the upper limit of conditional expression (3), the height of the light beam incident on the second lens unit from the optical axis becomes large, the lens units subsequent to the second lens unit become large, and the whole system can be made compact. If the lower limit of conditional expression (3) is exceeded, aberrations such as spherical aberration and astigmatism will be deteriorated, and the sensitivity to each aberration will be very high, and the manufacturing stability will be poor. .

If the value exceeds the upper limit of conditional expression (4), correction of aberrations such as curvature of field becomes insufficient, which is not desirable.

If the lower limit of conditional expression (4) is exceeded, the correction will be excessive, and the back focus will be long, making it difficult to make the whole system compact.

A glass material having a relatively high refractive index (about 1.7 or more) is used for the material of the negative lens in each lens group.
It is preferable to use a glass material having a relatively low refractive index (about 1.6 or less) for the positive lens.

According to this, the Petzval sum can be corrected well, and a more preferable embodiment can be obtained.

Hereinafter, numerical data of the embodiment of the rear converter lens according to the present invention and the main photographing lens to which the rear converter lens is attached will be shown. In these numerical examples, i indicates the order from the object side, ri is the radius of curvature of the i-th surface in order from the object side, and di is the lens between the i-th and i + 1-th order in order from the object side. The thickness or air gap, ni and νi are the refractive index and the Abbe number at the d-line of the i-th optical member in order from the object side.

In the numerical examples of the main photographing lens, the first and last two lens surfaces are glass blocks such as a face plate and a filter. Table 1 shows the relationship between the above-described conditional expressions and various numerical values in the numerical examples.

[0054]

[Outside 1]

[0055]

[Outside 2]

[0056]

[Outside 3]

[0057]

[Outside 4]

[0058]

[Table 1]

Next, an embodiment of a single-lens reflex camera system in which the rear converter lens of the present invention is mounted between the main taking lens and the camera body will be described with reference to FIG. In FIG. 7, reference numeral 10 denotes a single-lens reflex camera main body, 11 denotes a photographing optical system in which the rear converter lens of the present invention is mounted on a main photographing lens, and 12 denotes a film or an image sensor for recording a subject image obtained through the photographing optical system 11. Recording means, 1
Reference numeral 3 denotes a finder optical system for observing a subject image from the photographing optical system, and 14 denotes a recording means 1 for recording the subject image from the photographing optical system.
This is a rotating quick return mirror for switching and transmitting between the finder optical system 2 and the finder optical system 13. When observing the subject image with the viewfinder, the subject image formed on the focus plate 15 via the quick return mirror 14 is turned into an erect image by the pentaprism 16, and then enlarged and observed by the eyepiece optical system 17. At the time of photographing, the quick return mirror 14 rotates in the direction of the arrow, and the subject image is formed on the recording means 12 and recorded.

By applying the photographing optical system of the present invention to an optical device such as a single-lens reflex camera interchangeable lens as described above,
It is possible to realize a very compact optical device having a focal length obtained by expanding a focal length having high optical performance to a longer one.

[0061]

According to the present invention, a rear converter lens capable of satisfactorily correcting various aberrations, in particular, correcting field curvature satisfactorily, and always obtaining high optical performance even when attached to a main lens system, and a rear converter lens therefor. An optical device using the same can be achieved.

In addition, according to the present invention, a rear converter lens which can reduce the sensitivity of each lens group to aberration, is easy to manufacture, and can easily maintain high optical performance, and an optical apparatus using the same are achieved. can do.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view when the rear converter lens of Numerical Example 1 is mounted on a main photographing lens.

FIG. 2 is an aberration diagram when the rear converter lens of Numerical Example 1 is attached to a main photographing lens.

FIG. 3 is a cross-sectional view when the rear converter lens of Numerical Example 2 is attached to a main photographing lens.

FIG. 4 is an aberration diagram when the rear converter lens of Numerical Example 2 is attached to a main photographing lens.

FIG. 5 is a cross-sectional view when the rear converter lens of Numerical Example 3 is attached to a main photographing lens.

FIG. 6 is an aberration diagram when the rear converter lens of Numerical Example 3 is attached to a main photographing lens.

FIG. 7 is a schematic view of a main part of an embodiment of the optical apparatus of the present invention.

[Explanation of symbols]

 SP: aperture IP: image plane ML: main photographing lens RCL: rear converter lens S: sagittal image plane M: meridional image plane d: d-line 10: camera body 11: photographing optical system 12: recording means 13: viewfinder optical system 14 : Quick return mirror 15: Focus plate 16: Penta prism 17: Eyepiece

Claims (9)

[Claims] 1. A rear converter lens having a negative focal length which is detachably mounted on the image plane side of a main lens system to increase the focal length of the entire system, wherein the rear converter lenses are positively arranged in order from the object side. The first lens group has a refractive power, a second lens group has a negative refractive power, and a third lens group has a positive refractive power. The second lens group has, in order from the object side, a concave surface having both lens surfaces. 21 lenses, the second of which both lens surfaces are convex
The second lens unit includes a second lens unit and a third lens unit. The distance between the second lens unit and the third lens unit on the optical axis is BD2. A rear converter lens characterized by satisfying 0.09 <| BD2 / Ftl | <0.20 when the focal length of the entire system of the rear converter lens is Ftl. 2. The rear converter lens according to claim 1, wherein the twenty-first lens, the twenty-second lens, and the twenty-third lens are cemented to each other. 3. The rear converter lens according to claim 1, wherein 0.2 <F2 / Ftl <0.5 is satisfied, where F2 is a focal length of the second lens group. 4. The first lens group and the third lens group,
The rear converter lens according to claim 1, wherein the rear converter lens has one or more positive lenses and one or more negative lenses. 5. The first lens group includes, in order from the object side,
A meniscus lens of negative refractive power with the convex surface facing the object side,
5. The lens according to claim 1, wherein both the lens surfaces have a convex surface, and the third lens group includes, in order from the object side, a positive lens and a negative lens having a convex surface facing the image side. 6. Rear converter lens. 6. The first lens group includes, in order from the object side,
A meniscus lens of negative refractive power with the convex surface facing the object side,
The third lens group includes, in order from the object side, a meniscus lens having a positive refractive power with a convex surface facing the image side, and both lens surfaces including a negative refractive power lens having a concave surface. The rear converter lens according to any one of claims 1 to 4, wherein: 7. When the focal length of the i-th lens unit is Fi, 0.6 <| F1 / Ftl | <1.0 0.2 <F2 / Ftl <0.5 1.0 <| F3 / The rear converter lens according to claim 1, wherein Ftl | <2.0 is satisfied. 8. An optical system comprising the rear converter lens according to claim 1. Description: 9. An optical apparatus comprising the rear converter lens according to claim 1. Description: