JPH06337348A - Gauss type lens - Google Patents

Abstract

PURPOSE:To well correct various aberrations and more particularly chromatic aberrations and to obtain optical performance high over the entire part of object distances by adequately setting the lens constitution and glass materials of respective lenses. CONSTITUTION:This Gauss type lens consists of the lens constitution of 6 elements in four groups consisting, successively from an object side, of the combined lens GA of a negative refracting power as a whole formed by joining the first lens G1 of a positive refracting power, the convex face of which is directed to the object side, the second lens G2 of the positive refracting power, the convex face of which is directed to the object side, and the third lens of the negative refracting power, the concave face of which is directed to the image plane side, a stop SP, a combined lens GB of the negative refracting power as a whole formed by joining the fourth lens G4 of the negative refracting power, the concave face of which is directed to the object side, and the fifth lens G5 of the positive refracting power, the convex face of which is directed to the image plane side, and the sixth lens G6 of the positive refracting power, the convex face of which is directed to the image plane side. The conditions 1.64<Nd<1.66, 37<nud<39.0, 0.59<Pg, F<0.61 are satisfied when the refractive index, Abbe number and partial dispersion ratio of the material of the one lens among the first, second, fifth and sixth lenses are defined respectively as Nd, nud, Pg,F.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a Gauss type lens,
In particular, the present invention relates to a Gauss type lens suitable for a single-lens reflex camera such as a photographic camera or a video camera, which has excellent optical performance over the entire object distance by satisfactorily correcting chromatic aberration among various aberrations.

[0002]

2. Description of the Related Art Conventionally, in a single-lens reflex camera such as a photographic camera or a video camera, a rotary reflecting mirror is provided behind a taking lens to reflect a light beam from the taking lens and guide it to a finder system.

Therefore, there is a demand for a lens type for a photographing lens used in a single-lens reflex camera, which can easily obtain a long back focus to the extent that a rotary reflecting mirror is arranged and can easily obtain high optical performance. There is.

Conventionally, there is a so-called Gauss type lens as a photographing lens having a standard angle of view capable of achieving these requirements relatively easily, and it is most often used at present. The Gauss type lens is also used as a macro lens because it has little aberration variation with respect to variation of the object distance.

In general, in the Gauss type, in many cases, a glass material having a high refractive index is used as the material of the positive lens in order to reduce the Petzval sum and to favorably correct the field curvature. Further, the lens structure is configured to satisfactorily correct various aberrations in close-up photography and to reduce variations in various aberrations due to changes in the photographing magnification.

[0006]

When the photographing magnification of the Gauss type lens becomes high, for example, when it is used as a magnifying macro exceeding 1 ×, a large amount of chromatic aberration occurs.

In particular, since axial chromatic aberration increases in proportion to the square of the magnification, it becomes important to correct it.
Further, when a Gaussian lens is used as a standard angle-of-view lens for a large format camera, a lens for a plate-making camera, etc., the focal length becomes long, so that axial chromatic aberration increases proportionally.

Generally, chromatic aberration increases in proportion to the focal length. Therefore, when the focal length becomes long, chromatic aberration such as secondary spectrum is corrected by using, for example, fluorite or a glass material having anomalous dispersion close to fluorite.

However, an abnormally dispersible glass material such as fluorite has a problem that its physical and chemical stability is poor.
Further, since the refractive index is low, the curvature of the lens surface becomes strong, and a lot of high-order aberrations tend to occur.

The present invention uses a Gaussian type lens system,
By appropriately setting the lens configuration of each lens and the glass material, an F number that has high optical performance over the entire object distance in which chromatic aberration, among various aberrations, is well corrected.
The purpose is to provide a Gaussian lens of about 8 degrees.

[0011]

A Gaussian lens according to the present invention comprises a first lens having a positive refractive power having a convex surface directed toward the object side and a second lens having a positive refractive power having a convex surface facing the object side in order from the object side. A 23rd lens having a negative refracting power as a whole in which a lens and a third lens having a negative refracting power having a concave surface facing the image side are stuck together, a diaphragm, and a 4th having a negative refracting power having a concave surface facing the object side. The lens and the fifth lens having a positive refracting power with the convex surface facing the image plane side are bonded together, and as a whole, a 45th lens having a negative refracting power and a sixth lens having a positive refracting power are provided. The refractive index, the Abbe number, and the partial dispersion ratio of the material of at least one of the second, fifth, and sixth lenses are N _d , ν _d , P _g , and _{F, respectively.}
When

[0012]

[Equation 1] It is characterized by satisfying the following condition.

In particular, when the average value of the partial dispersions of the materials of the third lens and the fourth lens is P _g , _F , _a 0.58 <P _g , _F , _a <0.62 (2) Satisfying the following condition, the average value of the refractive index of the material of the third lens and the fourth lens is N _d , _a , and the average value of the Abbe number of the material of the third lens and the fourth lens Be ν _d , _a

[0014]

[Equation 2] It is characterized by satisfying the following conditions.

[0015]

1 to 4 are numerical examples 1 to 1 of the present invention.
4 is a lens cross-sectional view of FIG. In the figure, Gi is the i-th lens and SP
Is the aperture.

Generally, in a Gauss type lens, it is 2
Two negative lenses (G3, G4) are arranged on the diaphragm SP side with concave surfaces having a strong refractive power facing each other, and at least one positive lens is arranged on each of the object side and the image plane side of the two negative lenses. Then, the concave surface of the two negative lenses arranged with the diaphragm sandwiched between them and having a negative refractive power toward the diaphragm SP side mainly secures a predetermined back focus, reduces Petzval sum, and achieves flatness of the curvature of field. Moreover, various aberrations such as coma are corrected.

That is, in the Gauss type lens of the present invention, the first lens G having a positive refractive power whose convex surface faces the object side in order from the object side.
1. Second lens G2 having a positive refractive power with a convex surface facing the object side
And a cemented lens GA having a negative refracting power as a whole, in which a third lens having a negative refracting power with a concave surface facing the image side is cemented,
A diaphragm SP, and a negative refractive power as a whole in which a fourth lens G4 having a negative refractive power with a concave surface facing the object side and a fifth lens G5 having a positive refractive power having a convex surface facing the image side are cemented together. Lens GB, and a sixth lens element having a positive refractive power and having a convex surface directed toward the image side.
The lens group G6 is composed of 6 lenses in 4 groups.

In Numerical Embodiment 1, the first lens G1
In Numerical Example 2, the fifth lens, in Numerical Example 3 the first lens and the fifth lens, in Numerical Example 4 the first lens, the fifth lens, and the sixth lens, the above-mentioned conditional expression (1 ) ~
Secondary chromatic aberration is satisfactorily corrected by using a glass material having a high refractive index and anomalous dispersion satisfying (3).

For the negative lens, heavy flint glass, which is general glass, is used. As a result, various aberrations, particularly chromatic aberrations at a short-distance object (at a photographing magnification of 2 times and at the time of magnifying photographing) are satisfactorily corrected, and high optical performance is obtained over the entire object distance.

In the present invention, the partial dispersion ratio P _g , _F is defined as the refractive index at the F-line, C-line, and g-line of the Fraunhofer line is N _F , N _C , and N _g , respectively.

[0021]

[Equation 3] Is defined by the formula

As described above, the present invention properly corrects the aberration variation during focusing by appropriately setting the refractive index, Abbe number, partial dispersion ratio, etc. of the lens shape and material of each lens, and includes close-up photography. We have achieved a Gaussian lens with high optical performance over the entire object distance.

In this embodiment, the cemented lens G is used.
A and GB may be configured separately. Focusing may be performed not only by moving the entire lens system, but also by using floating in which lens groups in front of and behind the aperture stop SP are moved at different speeds.

Next, numerical examples of the present invention will be shown. In the numerical examples, Ri is the radius of curvature of the i-th lens surface in order from the object side, Di is the i-th lens thickness and air gap from the object side, and Ni and νi are respectively from the object side of the i-th lens. The refractive index of glass and the Abbe number.

Numerical Example 1 F = 35 Fno = 1: 2.8 Number RD N _d ν _d 1 24.104 1.85 1.650520 38.04 2 -236.387 0.20 3 11.045 3.94 1.743997 44.79 4 -76.773 0.80 Hospital 1.755199 27.51 5 Hospital 8.579 4.00 6 Restriction 5.70 7 -8.196 0.80 1.783000 36.15 8 70.653 2.65 1.639300 44.88 9 -12.857 0.20 10 -61.972 2.20 1.735199 41.08 11 -14.881 Numerical Example 2 F = 34.999 Fno = 1: 2.8 Number RD N _d ν _d 1 25.128 1.85 1.772499 49.60 2 1220.114 0.20 3 10.607 3.94 1.720000 43.71 4 59.091 0.80 1.755199 27.51 5 8.068 4.00 6 Aperture 5.70 7 -8.016 0.80 1.721507 29.24 8 -27.415 2.65 1.650520 38.04 9 -11.886 0.20 10 -40.683 2.20 1.735199 41.08 11 -16.057 Numerical Example 3 F = 35.044 Fno = 1 : 2.8 number _{RD N d ν d 1 22.413 1.85} 1.650520 38.04 2 345.100 0.20 3 10.876 3.94 1.717004 47.94 4 -92.191 0.80 1.721507 29.24 5 8.549 4.00 6 aperture 5.70 7 -7.962 0.80 1.721507 29.24 8 270.024 2.65 1.650520 38.04 9 -12.118 0.20 10 - 65.843 2.20 1.749497 35.27 11 -17.662 Numerical Example 4 F = 35.044 Fno = 1: 2.8 Number RD N _d ν _d 1 2 2.951 1.85 1.650520 38.04 2 -5212.230 0.20 3 10.528 3.94 1.717004 47.94 4 -68.068 0.80 1.721507 29.24 5 8.084 4.00 6 Aperture 5.70 7 -7.525 0.80 1.688930 31.08 8 40.661 2.65 1.650520 38.04 9 -12.241 0.20 10 -48.041 2.20 1.-14520.288.04

As described above, according to the present invention, by using the Gauss type lens system as described above and appropriately setting the lens configuration and glass material of each lens, an object in which chromatic aberration is corrected particularly well It is possible to achieve a Gaussian lens with an F number of about 2.8, which has high optical performance over the entire distance.

[Brief description of drawings]

FIG. 1 is a lens cross-sectional view of Numerical Example 1 of the present invention.

FIG. 2 is a lens cross-sectional view of Numerical Example 2 of the present invention.

FIG. 3 is a lens cross-sectional view of Numerical Example 3 of the present invention.

FIG. 4 is a lens cross-sectional view of Numerical Example 4 of the present invention.

FIG. 5 is an aberration diagram of Numerical example 1 of the present invention (magnification β = −
2)

FIG. 6 is an aberration diagram of Numerical example 2 of the present invention (magnification β = −
2)

FIG. 7 is an aberration diagram of Numerical example 3 of the present invention (magnification β = −
2)

FIG. 8 is an aberration diagram of Numerical example 4 of the present invention (magnification β = −
2)

[Explanation of symbols]

 Gi i-th lens SP diaphragm d d line g g line C C line F F line S sagittal image surface M meridional image surface h image height

Claims (3)

[Claims] 1. A first lens having a positive refractive power whose convex surface faces the object side in order from the object side, a second lens having a positive refractive power whose convex surface faces the object side, and a negative lens whose concave surface faces the image side. The second lens of negative refracting power as a whole cemented with the third lens of refracting power of
The third lens, the aperture stop, and the fourth lens having a negative refracting power with a concave surface facing the object side and the fifth lens having a positive refracting power with a convex surface facing the image side are cemented together to have a negative refracting power as a whole. 45 lenses,
And, having a sixth lens of positive refractive power, the first, second,
The refractive index and the Abbe number of the material of at least one of the fifth and sixth lenses, and the partial dispersion ratio are N _d ,
Gaussian type characterized by satisfying a condition of 1.64 <N _d <1.66 37 <ν _d <39 0.59 <P _g , _F <0.61 where ν _d , P _g , _F lens. 2. When the average value of the partial dispersions of the materials of the third lens and the fourth lens is P _g , _F , _a , the condition of 0.58 <P _g , _F , _a <0.62 is satisfied. The Gaussian lens according to claim 1, wherein 3. The average value of the refractive indices of the materials of the third lens and the fourth lens is N _d , _a , and the average value of the Abbe numbers of the materials of the third lens and the fourth lens is ν _d , _a . 3. The Gaussian lens according to claim 2, wherein the condition of 1.64 <N _d , _a <1.85 23 <ν _d , _a <38 is satisfied.