JPH1123961A5

JPH1123961A5 -

Info

Publication number: JPH1123961A5
Application number: JP1997177879A
Authority: JP
Filing date: 1997-07-03
Publication date: 2004-12-16

Description

【０００６】
【課題を解決するための手段】
上記目的を達成するために、本発明の広角レンズは、物体側から順に配列された負レンズと正レンズとからなる前群レンズと、全体として正の屈折力を有する後群レンズとからなり、前群レンズと後群レンズとの間に絞りを配置する広角レンズであって、後群レンズを、物体側から順に、正レンズ，負レンズ，正レンズ，正レンズの４枚のレンズにより構成するとともに、レンズ系全体での焦点距離をｆ、後群レンズの合成焦点距離をｆ₂₀、４枚のレンズ中最も像面側に位置する正レンズの焦点距離をｆ₂₄、最も物体側に位置する正レンズの屈折率をＮ₂₁、負レンズの屈折率をＮ₂₂としたときに、
１．１＜ｆ₂₀／ｆ＜１．８
１．２＜ｆ₂₄／ｆ＜２．４
Ｎ₂₁ ＞１．７
Ｎ₂₂ ＞１．８
なる各条件を満たすようにするものである。[0006]
[Means for solving the problem]
In order to achieve the above object, the wide-angle lens of the present invention is a wide-angle lens comprising a front lens group consisting of a negative lens and a positive lens arranged in order from the object side, and a rear lens group having a positive refractive power overall , with an aperture located between the front lens group and the rear lens group, wherein the rear lens group is composed of four lenses, in order from the object side, a positive lens, a negative lens, a positive lens, and a positive lens, and when the focal length of the entire lens system is f, the composite focal length of the rear lens group is _f20 , the focal length of the positive lens located closest to the image plane among the four lenses _{is f24} , the refractive index of the positive lens located closest to the object side is _N21 , and the refractive index of the negative lens is _N22 , then:
1.1 < f ₂₀ /f < 1.8
1.2 < f ₂₄ /f < 2.4
N ₂₁ > 1.7
N ₂₂ > 1.8
The purpose is to satisfy the following conditions.

【０００８】
【作用】
絞りの像面側に配置される後群レンズを、物体側より順に、正レンズ，負レンズ，正レンズ，正レンズの４枚のレンズにより構成し、後群レンズ中の負レンズと絞りとの間に正レンズを配置することで、後群負レンズの屈折力を強くでき、前群レンズ中の負レンズの屈折力とのバランスがとれて負の歪曲収差の増大を抑えることができる。また、絞りが後群負レンズから離れるため、負レンズを通る光線高が高くなり、非点収差やコマ収差が増大するが、これらの収差は後群レンズ中の負レンズの屈折率を高く、すなわち、条件式
Ｎ₂₂ ＞１．８
を満たすことにより補正することができる。また、これにより増大するペッツバール和は、条件式
Ｎ₂₁ ＞１．７
を満たすことにより抑えられ、像面湾曲の悪化を防止することができる。[0008]
[Effect]
The rear lens group arranged on the image plane side of the aperture stop is composed of four lenses, in order from the object side, a positive lens, a negative lens, a positive lens, and a positive lens, and by arranging the positive lens between the negative lens in the rear lens group and the aperture stop, the refractive power of the negative lens in the rear lens group can be strengthened, and a balance with the refractive power of the negative lens in the front lens group can be achieved, thereby suppressing an increase in negative distortion aberration. Also, since the aperture stop is located away from the negative lens in the rear lens group, the height of the light passing through the negative lens increases, and astigmatism and coma aberration increase, but these aberrations can be suppressed by increasing the refractive index of the negative lens in the rear lens group, that is, by satisfying the conditional formula _N22 >1.8.
The Petzval sum, which increases as a result of this, can be corrected by satisfying the condition N ₂₁ >1.7.
By satisfying the above condition, the curvature of field can be suppressed and the deterioration of the curvature of field can be prevented.

【０００９】
また、条件式
１．１＜ｆ₂₀／ｆ＜１．８
を満たすことにより、前群レンズ中の負レンズの屈折力と後群レンズの正の屈折力とのバランスを保ち、歪曲収差の発生を抑えることができる。この条件式の上限を越えると、後群レンズが十分な屈折力を持たなくなるため、レンズ系の全長が長くなってしまう。無理に全長を短くしようとすると、前群レンズ側にかかる負担が大きくなり、負の屈折力が強くなりすぎて歪曲収差の増大を抑えることができなくなる。一方、下限を越えると、レンズ系の全長は短縮しやすくなるものの、後群レンズの正の屈折力が強くなりすぎ、ペッツバール和が増大して像面湾曲が悪化する。[0009]
Furthermore, the conditional expression 1.1<f ₂₀ /f<1.8
By satisfying this condition, the balance between the refractive power of the negative lens in the front lens group and the positive refractive power of the rear lens group can be maintained, thereby suppressing the occurrence of distortion. If the upper limit of this condition is exceeded, the rear lens group will no longer have sufficient refractive power, resulting in an increase in the overall length of the lens system. If an attempt is made to shorten the overall length, the burden on the front lens group will increase, resulting in an excessively strong negative refractive power and making it impossible to suppress an increase in distortion. On the other hand, if the lower limit is exceeded, although it is easier to shorten the overall length of the lens system, the positive refractive power of the rear lens group will become too strong, increasing the Petzval sum and worsening the curvature of field.

【００１２】
【実施例】
図１は、本発明の広角レンズの構成を示すものである。広角レンズ５は、物体側より順に配列された負レンズと正レンズとからなる前群レンズ１０と、全体として正の屈折力の後群レンズ２０とによって構成されている。前群レンズ１０と後群レンズ２０との間には絞りＳＴＯが設けられ、後群レンズ２０の像面側には光学ローパスフィルターとしての平行ガラス３０が配置される。[0012]
[Example]
1 shows the configuration of a wide-angle lens of the present invention. The wide-angle lens 5 is composed of a front lens group 10 consisting of a negative lens and a positive lens arranged in that order from the object side, and a rear lens group 20 with an overall positive refractive power. An aperture stop STO is provided between the front lens group 10 and the rear lens group 20, and a parallel glass plate 30 serving as an optical low-pass filter is arranged on the image plane side of the rear lens group 20.

【００４８】
【発明の効果】
以上のように本発明の広角レンズによれば、絞りの像面側に配置される後群レンズが物体側より順に、正レンズ，負レンズ，正レンズ，正レンズの４枚のレンズにより構成され、後群レンズ中の負レンズと絞りとの間には正レンズが配置されるので、レンズ系の前群レンズ中の負レンズがもつ強い負の屈折力が分散され、負の歪曲収差の増大を抑えることができる。この際、非点収差やコマ収差が増大するが、これらの収差は後群レンズ中の負レンズの屈折力を強くすることで補正することができる。[0048]
[Effects of the Invention]
As described above, in the wide-angle lens of the present invention, the rear lens group, located on the image plane side of the aperture stop, is composed of four lenses: a positive lens, a negative lens, a positive lens, and a positive lens, in that order from the object side, and a positive lens is located between the negative lens in the rear lens group and the aperture stop, so that the strong negative refractive power of the negative lens in the front lens group of the lens system is dispersed, making it possible to suppress an increase in negative distortion. In this case, astigmatism and coma aberration increase, but these aberrations can be corrected by strengthening the refractive power of the negative lens in the rear lens group.

【００４９】
また、後群レンズの合成焦点距離を調整することで、前群レンズ中の負レンズがもつ負の屈折力と後群レンズの正の屈折力とのバランスを保ち、歪曲収差の発生を抑えることができる。また、後群レンズ中で最も像面側に位置する正レンズの焦点距離を調整することにより、レンズ系の全長を延ばすことなく、バックフォーカスを十分に長くすることができる。これにより、後群レンズと像面との間に、光学ローパスフィルターや、固体撮像素子の受光面に被せるカバーガラス等を配置するためのスペースを確保することができる。[0049]
In addition, by adjusting the composite focal length of the rear lens group, the negative refractive power of the negative lens in the front lens group can be balanced with the positive refractive power of the rear lens group, thereby suppressing distortion. Furthermore, by adjusting the focal length of the positive lens in the rear lens group that is located closest to the image plane, the back focus can be made sufficiently long without increasing the overall length of the lens system. This allows space to be secured between the rear lens group and the image plane for arranging an optical low-pass filter, a cover glass to cover the light-receiving surface of the solid-state image sensor, etc.

Claims

A wide-angle lens comprising a front lens group consisting of a negative lens and a positive lens arranged in that order from the object side, and a rear lens group having a positive refractive power as a whole, with an aperture stop disposed between the front lens group and the rear lens group,
The rear lens group is composed of four lenses, in order from the object side, a positive lens, a negative lens, a positive lens, and a positive lens; when the focal length of the entire lens system is f, the composite focal length of the rear lens group is _f20 , the focal length of the positive lens located closest to the image plane among the four lenses _{is f24} , the refractive index of the positive lens located closest to the object side is _N21 , and the refractive index of the negative lens is _N22 , then:
1.1 < f ₂₀ /f < 1.8
1.2 < f ₂₄ /f < 2.4
N ₂₁ > 1.7
N ₂₂ > 1.8
A wide-angle lens characterized by satisfying the following conditions.