JP4298028B2 - Converter lens - Google Patents
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【０００１】
【発明の属する技術分野】
本発明は、レンズ系の前方に装着してレンズ系全体の焦点距離を長い方、又は短い方に変位させるコンバーターレンズに関し、特に従来のコンバーターに対して色収差を大幅に改善したビデオカメラや電子スチルカメラ、銀塩写真用カメラ等に好適なコンバーターレンズに関するものである。
【０００２】
【従来の技術】
従来より、撮影レンズの前方に装着し全系の焦点距離を長焦点距離側に変化させるフロント方式のテレコンバーターレンズ（テレコンバーター）が、例えば特開昭55-32046号公報で提案されている。
【０００３】
テレコンバーターは多くの場合、正の屈折力を有する前群と負の屈折力を有する後群の２つのレンズ群を両レンズ群の焦点距離の和だけ主点間隔を隔てて配置し、全系としてアフォーカル系を構成している。従って最も簡単なレンズ系としては正と負の屈折力の２枚のレンズで構成することができる。しかしながら高い光学性能を得る為には収差補正上、２枚のレンズの構成では困難である。
【０００４】
一方、色収差の発生を抑制する方法として近年、回折光学素子を撮像光学系に応用する提案がなされている。例えば、特開平4-213421号公報では回折光学素子を応用することで色収差の低減を図った狭視野望遠鏡を開示している。又、特開平7-311346号公報ではアフォーカルの望遠鏡に回折光学素子を応用したズーム望遠鏡を開示している。
【０００５】
この他、特開平6-324262号公報では、少なくとも１枚の正の屈折力を持った回折光学素子と、少なくとも１枚の正の屈折力を持った屈折光学素子と、少なくとも１枚の負の屈折力を持った屈折光学素子より構成されたＦナンバーＦ２．８程度の色収差が比較的良好に補正された望遠レンズを開示している。又、特開平6-331887号公報も同様に、回折光学素子と屈折光学素子を組み合わせ、色収差が比較的良好に補正されたＦナンバーＦ２．８程度の望遠レンズを開示している。
【０００６】
【発明が解決しようとする課題】
テレコンバーターにおいてアフォーカル倍率を上げつつ光学系を小型化する為には、各レンズ群の屈折力を強める必要があるが、この際、各レンズ群で発生する収差を十分に補正することが困難になってくる。
【０００７】
本発明は、第１レンズと第２レンズの２つのレンズを有し、このうち１つのレンズ面に回折光学素子を導入し、回折光学的な作用と屈折系の色消し効果を合成することで、特に望遠端付近における色収差の補正効果を高めたコンバーターレンズの提供を目的とする。
【０００８】
【課題を解決するための手段】
請求項１の発明のコンバーターレンズは、レンズ系の物体側に装着し、レンズ系全体の焦点距離を変化させるコンバーターレンズであって、正の第１レンズと、負の第２レンズと、互いに分散の異なる材質より成る２層構造の回折光学素子より構成され、物体側より順に前記第１レンズと前記第２レンズが配置され、前記回折光学素子は前記第１レンズ又は前記第２レンズのいずれか１つのレンズ面に形成されており、前記第１レンズと前記第２レンズの焦点距離を各々ｆ１，ｆ２としたとき、
１．２５＜｜ｆ１／ｆ２｜＜２．５
なる条件を満足することを特徴としている。
請求項２の発明は請求項１の発明において、前記回折光学素子は正の屈折力を有することを特徴としている。
請求項３の発明は請求項１又は２の発明において、前記回折光学素子は、前記第１レンズの像面側の面に設けられていることを特徴としている。
請求項４の発明は請求項１又は２の発明において、前記回折光学素子は、前記第２レンズの物体側の面に設けられていることを特徴としている。
【０００９】
請求項５の発明のカメラは、請求項１乃至４のいずれか１項に記載のコンバーターレンズを有することを特徴としている。
【００１０】
【発明の実施の形態】
図１は本発明の実施形態１のコンバーターレンズを撮影レンズの光軸上前方に装着したときの要部概略図である。同図において、Ｃはコンバーターレンズ( コンバーター) 、Ｍは撮影レンズであり、ズームレンズより成っている。尚、撮影レンズＭは単一焦点距離のレンズ系であっても良い。
【００１１】
本実施形態のコンバーターレンズＣは、撮影レンズＭの光軸上前方に装着して全系の焦点距離を長い方へ変位させるテレコンバーターレンズとしての光学作用をしている。コンバーターレンズＣは、物体側より順に両レンズ面が凸面の正の屈折力の第１レンズＬ１と両レンズ面が凹面の負の屈折力の第２レンズＬ２を有している。撮影レンズＭは、物体側より順に変倍及び合焦の際に固定の正の屈折力の第１群Ｍ１、変倍機能を有する負の屈折力の第２群Ｍ２、正の屈折力の第３群Ｍ３、そして変倍により変動する像面を補正する補正機能と合焦機能の双方の機能を有する正の屈折力の第４群Ｍ４の４つのレンズ群を有している。ＳＰは絞り、ＦＰはフレアー絞り、Ｇはフィルター等のガラスブロック、ＩＰは像面である。
【００１２】
本実施形態のコンバーターＣは、第１レンズＬ１と第２レンズＬ２の主点間隔を第１レンズＬ１と第２レンズＬ２の焦点距離の和に略等しくしており、これにより全体として略アフォーカル系を構成している。
【００１３】
本実施形態では、第１レンズ、又は第２レンズのうち少なくとも１つのレンズ面に光軸に対して回転対称な回折光学素子を導入することで、特に撮影レンズとしてズームレンズを用いたときに、望遠端で大きく発生する軸上色収差を効果的に補正している。
【００１４】
本実施形態では、このような回折光学素子を屈折面と併用すると回折面と屈折面では同符号の屈折力でもある基準波長に対する色収差の出方が逆方向である為、屈折面で発生する色収差を補正することができる。又、このような回折光学素子は大きな異常分散性を有している為、２次スペクトルの補正に関しても通常ガラスよりも大きな効果を持っている。
【００１５】
一般に、テレコンバーターを主レンズ系の前方に配置したとき、望遠端においてはかなり色収差、特に軸上色収差が大きくなるが、本発明では正の屈折力を有する回折光学素子を導入することで、特に従来のテレコンバーターで大きく発生する色収差を効果的に補正している。
【００１６】
そして、第１レンズの焦点距離ｆ１と第２レンズの焦点距離ｆ２の比が、前述の条件式（１）を満足するようにしている。条件式（１）の下限以下では、テレコンバーターとしての倍率が小さく回折光学素子を導入する程の必要性がなく、逆に上限を超えると球面収差等の他の収差の補正が困難になる。
【００１７】
本実施形態では、カメラの撮影レンズに適用した場合を示したが、これに限定するものではなく、ビデオカメラの撮影レンズ、事務機のイメージスキャナーやデジタル複写機のリーダーレンズ等に使用しても同様の効果が得られる。
【００１８】
回折光学素子の格子形状は、その周期をＰ，波長をλ，回折次数をｍとすると、入射光線をＰｓｉｎθ＝ｍλに基づく角度θ方向に回折している。回折光学素子により回折作用を得る為の格子形状の具体的な構造はキノフォーム型、連続的な位相分布を階段状に近似したバイナリー型、微少な周期構造を３角波形状に近似し、構成した鋸歯型等が適用できる。
【００１９】
本実施形態で用いている回折光学素子の構成としては図６に示す１層のキノフォーム形状の１層構成のものや、図８に示すような格子厚の異なる（又は同一の）２つの層を積層した２層構成のもの等が適用可能である。
【００２０】
図７は図６に示す回折光学素子１０１の１次回折光の回折効率の波長依存特性である。実際の回折光学素子１０１の構成は、基材１０２の表面に紫外線硬化樹脂を塗布し、樹脂部に波長５３０ｎｍで１次回折光の回折効率が１００％となるような格子厚ｄの層１０３を形成している。
【００２１】
図７で明らかなように設計次数の回折効率は最適化した波長５３０ｎｍから離れるに従って低下し、一方設計次数近傍の次数の０次回折光と２次回折光の回折効率が増大している。その設計次数以外の回折光の増加はフレアとなり、光学系の解像度の低下につながる。
【００２２】
図８に示す２つの層１０４，１０５を積層した積層型の回折光学素子の１次回折光の回折効率の波長依存特性を図９に示す。
【００２３】
図８では基材１０２上に紫外線硬化樹脂（ｎｄ＝１．４９９，νｄ＝５４）からなる第１層１０４を形成し、その上に別の紫外線硬化樹脂（ｎｄ＝１．５９８，νｄ＝２８）からなる第２層１０５を形成している。この材質の組み合わせでは、第１層１０４の格子厚ｄ１はｄ１＝１８．８μｍ、第２の層１０５の格子厚ｄ２はｄ２＝１０．５μｍとしている。
【００２４】
図９から分かるように積層構造の回折光学素子にすることで、設計次数の回折効率は、使用波長全域で９５％以上の高い回折効率を有している。
【００２５】
なお、前述の積層構造の回折光学素子として、材質を紫外線硬化樹脂に限定するものではなく、他のプラスチック材等も使用できるし、基材によっては第１の層１０４を直接基材に形成しても良い。また各格子厚が必ずしも異なる必要はなく、材料の組み合わせによっては図１０に示すように２つの層１０４と１０５の格子厚を等しくしても良い。
【００２６】
この場合は、回折光学素子の表面に格子形状が形成されないので、防塵性に優れ、回折光学素子の組立作業性を向上させることができる。
【００２７】
以上のように、本実施形態では第１レンズと第２レンズの少なくとも１つのレンズ面に光軸に対して回転対称の回折光学素子を設け、その位相を適切に設定し、これにより第１レンズと第２レンズで発生する色収差を低減している。
【００２８】
本実施形態における回折光学素子は、ホログラフィック光学素子（ＨＯＥ）の製作手法であるリソグラフィック手法で２値的に製作している。回折光学素子はバイナリーオプティックス（ＢＩＮＡＲＹ ＯＰＴＩＣＳ）で製作しても良い。この場合、更に回折効率を上げるためにキノフォームと呼ばれる鋸状の形状にしても良い。またこれらの方法で製作した方によって成型により製造しても良い。
【００２９】
また本実施形態における回折光学素子の形状は、位相係数をC2i 基準波長（ｄ線）をλ、光軸からの距離をｈ、位相をφ（ｈ）としたとき
φ(h) ＝2 π／λ(C2・h2+C4・h4+C6・h6+ …C2i・h2i)
の式で表されるものである。
【００３０】
そして前述の位相係数Ｃ２を変化させることにより、近軸的な屈折力及び基準波長に対する色収差をコントロールしている。又、位相係数Ｃ４以降の高次の項の係数は、回折光学素子面の光線入射高の変化に対する屈折力変化を非球面と類似した効果を得ると同時に、光線高の変化に応じて基準波長に対する色収差のコントロールをしている。
【００３１】
本発明においては、第１レンズの２次位相係数をＣ２１、第２レンズの２次の位相係数をＣ２２、全系の焦点距離をｆｔとしたとき、
1.0 ×10-3＜Σ｜C21・f12 ＋C22・f22 ｜／ft＜2.0 ×10-2…（２）
の範囲とするのが良い。
【００３２】
条件式の下限を超えると色収差の補正が不十分となり、逆に上限を超えると過剰になってかえって色収差が悪化する。
【００３３】
回折光学素子は、数値実施例１、３のように第１レンズの像面側の面に設けても良い。又、数値実施例２のように第２レンズの物体側の面に設けても良い。又、参考例１のように第１，２レンズの両方に設けると更に収差が良好に補正できる。又、数値実施例３のようにプラスチックレンズを用いると光学系全体の軽量化を達成できる。
【００３４】
次に本発明のコンバーターレンズとそれを装着した撮影レンズＭの数値実施例を示す。数値実施例においてｒｉは物体側より順に第ｉ番目のレンズ面の曲率半径、ｄｉは物体側より順に第ｉ番目のレンズ厚及び空気間隔、ｎｉとνｉは各々物体側より順に第ｉ番目のレンズのガラスの屈折率とアッベ数である。又、前述の各条件式と数値実施例の関係を表−１に示す。
【００３５】
非球面形状は光軸方向にＸ軸、光軸と垂直方向にＹ軸、光の進行方向を正としＲを近軸曲率半径、Ｋ，Ｂ，Ｃ，Ｄ，Ｅ，Ｆを各々非球面係数としたとき、
なる式で表している。又「Ｄ−０Ｘ」は「１０-X」を意味している。
【００３６】
【数１】
実施例1 1.33倍
r 1= 40.871 d 1= 9.50 n 1= 1.51633 ν 1= 64.2
*r 2= -125.482 d 2= 9.53
r 3= -59.831 d 3= 1.80 n 2= 1.51633 ν 2= 64.2
r 4= 38.376
r 2 面(回折面) C2=-1.32663×10-4 C4=-2.62248×10-8
実施例2 1.29倍
r 1= 41.203 d 1= 9.50 n 1= 1.48749 ν 1= 70.2
r 2= -83.303 d 2= 7.97
*r 3= -50.684 d 3= 1.80 n 2= 1.51633 ν 2= 64.2
r 4= 42.850
r 3 面(回折面) C2=-7.90734×10-5 C4=-7.79424×10-8
参考例１ 1.75倍
r 1= 38.506 d 1= 12.00 n 1= 1.51633 ν 1= 64.2
*r 2=-2033.783 d 2= 20.77
*r 3= -103.091 d 3= 1.80 n 2= 1.69680 ν 2= 55.5
r 4= 42.144
r 2 面(回折面) C2=-7.83985×10-4 C4= 2.29230×10-7
r 3 面(回折面) C2= 1.42721×10-3 C4=-1.10013×10-6
実施例3 1.33倍
r 1= 39.458 d 1= 9.50 n 1= 1.49171 ν 1= 57.4
*r 2= -115.271 d 2= 9.52
r 3= -55.654 d 3= 1.80 n 2= 1.49171 ν 2= 57.4
r 4= 37.122
r 2 面(回折面) C2=-1.50965×10-4 C4=-3.11922×10-8
主レンズ系 f=64.09166
r 1= 48.324 d 1= 1.30 n 1= 1.84666 ν 1= 23.8
r 2= 25.164 d 2= 5.70 n 2= 1.60311 ν 2= 60.6
r 3= -210.564 d 3= 0.17
r 4= 21.166 d 4= 3.10 n 3= 1.69680 ν 3= 55.5
r 5= 51.698 d 5= 21.33
r 6= 53.276 d 6= 0.65 n 4= 1.77250 ν 4= 49.6
r 7= 5.383 d 7= 2.65
r 8= -12.927 d 8= 0.60 n 5= 1.69680 ν 5= 55.5
r 9= 12.927 d 9= 0.85
r10= 12.407 d10= 1.55 n 6= 1.84666 ν 6= 23.8
r11= 84.497 d11= 1.30
r12=( 絞り ) d12= 1.20
*r13= 7.654 d13= 3.40 n 7= 1.58313 ν 7= 59.4
*r14= 104.107 d14= 0.20
r15= 10.242 d15= 0.60 n 8= 1.84666 ν 8= 23.8
r16= 6.539 d16= 1.59
r17= 30.954 d17= 1.60 n 9= 1.51633 ν 9= 64.1
r18= -30.954 d18= 1.70
r19= ∞ d19= 7.50
r20= 12.613 d20= 2.50 n10= 1.60311 ν10= 60.6
r21= -12.613 d21= 0.50 n11= 1.84666 ν11= 23.8
r22= -33.464 d22= 3.00
r23= ∞ d23= 3.69 n12= 1.51633 ν12= 64.1
r24= ∞
r13 面(非球面) K=-2.58314 B=-2.58314 C=5.75642×10-4
D=-6.74713×10-6 E= 7.18668×10-8
r14 面(非球面) K= 1.80987×102 B= 7.32779×10-5
C=-4.13717×10-6
【００３７】
【表１】
【００３８】
【発明の効果】
本発明によれば以上のように、第１レンズと第２レンズの２つのレンズを有し、このうち少なくとも１つのレンズ面に回折光学面を導入し、回折光学的な作用と屈折系の色消し効果を合成することで、特に望遠端付近における色収差の補正効果を高めたコンバーターレンズを達成することができる。
【図面の簡単な説明】
【図１】 本発明の数値実施例１のコンバーターレンズを撮影レンズの光軸上前方に装着したときの説明図
【図２】 本発明の数値実施例１のコンバーターレンズを撮影レンズの光軸上前方に装着したときの収差図
【図３】 本発明の数値実施例２のコンバーターレンズを撮影レンズの光軸上前方に装着したときの収差図
【図４】 本発明の参考例１のコンバーターレンズを撮影レンズの光軸上前方に装着したときの収差図
【図５】 本発明の数値実施例３のコンバーターレンズを撮影レンズの光軸上前方に装着したときの収差図
【図６】 本発明の参考例に係る回折光学素子の説明図
【図７】 本発明の参考例に係る回折光学素子の波長依存特性の説明図
【図８】 本発明に係る回折光学素子の説明図
【図９】 本発明に係る回折光学素子の波長依存特性の説明図
【図１０】 本発明に係る回折光学素子の説明図
【符号の説明】
Ｃ コンバーターレンズ
Ｍ 撮影レンズ
Ｌ１ 第１レンズ
Ｌ２ 第２レンズ
ｄ ｄ線
ｇ ｇ線
ΔＳ サジタル像面
ΔＭ メリディオナル像面[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a converter lens that is mounted in front of a lens system and displaces the focal length of the entire lens system to be longer or shorter, and in particular, video cameras and electronic stills that have greatly improved chromatic aberration compared to conventional converters. The present invention relates to a converter lens suitable for a camera, a silver salt photographic camera and the like.
[0002]
[Prior art]
Conventionally, a front-type teleconverter lens (teleconverter) that is mounted in front of a photographing lens and changes the focal length of the entire system to the long focal length side has been proposed in, for example, Japanese Patent Laid-Open No. 55-32046.
[0003]
Teleconverters often arrange two lens groups, a front group having a positive refractive power and a rear group having a negative refractive power, with the sum of the focal lengths of both lens groups being separated by a principal point interval. Configures an afocal system. Therefore, the simplest lens system can be composed of two lenses having positive and negative refractive powers. However, in order to obtain high optical performance, it is difficult to correct the aberration with the configuration of two lenses.
[0004]
On the other hand, as a method for suppressing the occurrence of chromatic aberration, proposals have recently been made to apply a diffractive optical element to an imaging optical system. For example, Japanese Patent Application Laid-Open No. 4-134221 discloses a narrow-field telescope that reduces chromatic aberration by applying a diffractive optical element. Further, in JP-A 7-311346 JP discloses a zoom telescope of applying a diffractive optical element to telescope afocal.
[0005]
In addition, JP-A-6-324262 discloses at least one diffractive optical element having positive refractive power, at least one refractive optical element having positive refractive power, and at least one negative optical element. There is disclosed a telephoto lens in which a chromatic aberration of about F number F2.8, which is composed of a refractive optical element having refractive power, is corrected relatively well. Similarly, Japanese Patent Laid-Open No. 6-331887 also discloses a telephoto lens having an F number of about F2.8 in which a diffractive optical element and a refractive optical element are combined and chromatic aberration is corrected relatively well.
[0006]
[Problems to be solved by the invention]
In order to reduce the size of the optical system while increasing the afocal magnification in the teleconverter, it is necessary to increase the refractive power of each lens group. At this time, it is difficult to sufficiently correct the aberration generated in each lens group. It becomes.
[0007]
The present invention has two lenses of the first lens and the second lens, the diffractive optical element is introduced into Of this Chi one lens surface, to synthesize an achromatic effect of refraction system and a diffraction optical effects Thus, an object of the present invention is to provide a converter lens with an enhanced correction effect of chromatic aberration particularly near the telephoto end.
[0008]
[Means for Solving the Problems]
The converter lens according to the first aspect of the present invention is a converter lens that is attached to the object side of the lens system and changes the focal length of the entire lens system, and the positive first lens and the negative second lens are dispersed with respect to each other. The first lens and the second lens are arranged in order from the object side, and the diffractive optical element is either the first lens or the second lens. Formed on one lens surface, and the focal lengths of the first lens and the second lens are f1 and f2, respectively.
1.25 <| f1 / f2 | <2.5
It is characterized by satisfying the following conditions.
According to a second aspect of the present invention, in the first aspect of the invention, the diffractive optical element has a positive refractive power.
According to a third aspect of the present invention, in the first or second aspect of the present invention, the diffractive optical element is provided on a surface on the image plane side of the first lens.
According to a fourth aspect of the present invention, in the first or second aspect of the present invention, the diffractive optical element is provided on an object side surface of the second lens.
[0009]
According to a fifth aspect of the present invention, there is provided a camera having the converter lens according to any one of the first to fourth aspects.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a schematic view of a main part when the converter lens according to the first embodiment of the present invention is mounted on the front side of the optical axis of the photographing lens. In the figure, C is a converter lens (converter), M is a photographing lens, and is composed of a zoom lens. The taking lens M may be a lens system having a single focal length.
[0011]
The converter lens C of the present embodiment has an optical action as a teleconverter lens that is mounted in front of the photographing lens M on the optical axis and displaces the focal length of the entire system in the longer direction. The converter lens C includes, in order from the object side, a first lens L1 having a positive refractive power whose both lens surfaces are convex and a second lens L2 having a negative refractive power whose both lens surfaces are concave. The photographic lens M includes, in order from the object side, a first group M1 having a fixed positive refractive power during zooming and focusing, a second group M2 having a negative refractive power having a zooming function, and a first group having a positive refractive power. The third lens unit M3 includes four lens units including a third lens unit M3 and a fourth lens unit M4 having a positive refractive power that has both a correction function for correcting an image plane fluctuating due to zooming and a focusing function. SP is a diaphragm, FP is a flare diaphragm, G is a glass block such as a filter, and IP is an image plane.
[0012]
In the converter C of the present embodiment, the distance between the principal points of the first lens L1 and the second lens L2 is substantially equal to the sum of the focal lengths of the first lens L1 and the second lens L2, thereby substantially afocal as a whole. The system is configured.
[0013]
In the present embodiment, by introducing the rotationally symmetric diffractive optical element in at least one lens surface of the first lens or the second lens with respect to the optical axis, when a zoom lens as a particular photographing lens This effectively corrects the axial chromatic aberration that occurs greatly at the telephoto end.
[0014]
In the present embodiment, since the chromatic aberration of attitude for such diffraction reference wavelength which is also the power of the same sign in refractive surface and in combination with refractive surface and the diffraction surface of the optical element are opposite, generated by the refracting surface Chromatic aberration can be corrected. Further, it has a greater effect than ordinary glass also for such diffraction optical element because it has a large anomalous dispersion, the secondary spectrum correction.
[0015]
Generally, when placing the tele-converter in front of the main lens system, considerable chromatic aberration at the telephoto end, particularly axial chromatic aberration is increased, in the present invention by introducing a diffractive optical element having a positive refractive power, in particular It effectively corrects chromatic aberrations that occur greatly in conventional teleconverters.
[0016]
The ratio between the focal length f1 of the first lens and the focal length f2 of the second lens satisfies the above-described conditional expression (1). Below the lower limit of conditional expression (1), the magnification as a teleconverter is small and there is no need to introduce a diffractive optical element. Conversely, when the upper limit is exceeded, it is difficult to correct other aberrations such as spherical aberration.
[0017]
In the present embodiment, the case where the present invention is applied to a camera photographing lens is shown, but the present invention is not limited to this, and the present invention is not limited to this. Similar effects can be obtained.
[0018]
Grating shape of the diffractive optical element has its period P, and the wavelength lambda, the diffraction order is m, is diffracted to the angle θ direction based on the incident light to Psinθ = mλ. The specific structure of the grating shape for obtaining the diffractive action by the diffractive optical element is a kinoform type, a binary type approximating a continuous phase distribution in a staircase shape, and a fine periodic structure approximating a triangular wave shape. A saw-tooth type or the like can be applied.
[0019]
As the configuration of the diffractive optical element used in the present embodiment, a single-layer kinoform-shaped configuration shown in FIG. 6 or two layers having different (or the same) grating thickness as shown in FIG. A two-layer structure in which layers are stacked can be applied.
[0020]
FIG. 7 shows the wavelength dependence characteristics of the diffraction efficiency of the first-order diffracted light of the diffractive optical element 101 shown in FIG. The actual configuration of the diffractive optical element 101 is that an ultraviolet curable resin is applied to the surface of the substrate 102, and a layer 103 having a grating thickness d is formed on the resin portion so that the diffraction efficiency of the first-order diffracted light is 100% at a wavelength of 530 nm. is doing.
[0021]
As is apparent from FIG. 7, the diffraction efficiency of the designed order decreases with increasing distance from the optimized wavelength of 530 nm, while the diffraction efficiency of the 0th order diffracted light and the second order diffracted light near the designed order increases. An increase in the diffracted light other than the design order becomes a flare, which leads to a decrease in the resolution of the optical system.
[0022]
FIG. 9 shows the wavelength dependence characteristics of the diffraction efficiency of the first-order diffracted light of the laminated diffractive optical element in which the two layers 104 and 105 shown in FIG. 8 are laminated.
[0023]
In FIG. 8, a first layer 104 made of an ultraviolet curable resin (nd = 1.499, νd = 54) is formed on a substrate 102, and another ultraviolet curable resin (nd = 1.598, νd = 28) is formed thereon. ) Is formed. In this combination of materials, the lattice thickness d1 of the first layer 104 is d1 = 18.8 μm, and the lattice thickness d2 of the second layer 105 is d2 = 10.5 μm.
[0024]
As can be seen from FIG. 9, by using a diffractive optical element having a laminated structure, the diffraction efficiency of the designed order has a high diffraction efficiency of 95% or more over the entire operating wavelength range.
[0025]
Note that the diffractive optical element having the above-described laminated structure is not limited to the ultraviolet curable resin, and other plastic materials can be used. Depending on the base material, the first layer 104 is directly formed on the base material. May be. Further, the lattice thicknesses are not necessarily different, and depending on the combination of materials, the lattice thicknesses of the two layers 104 and 105 may be equal as shown in FIG.
[0026]
In this case, since the grating shape is not formed on the surface of the diffractive optical element, it is excellent in dust resistance and can improve the assembling workability of the diffractive optical element.
[0027]
As described above, in this embodiment, a diffractive optical element that is rotationally symmetric with respect to the optical axis is provided on at least one lens surface of the first lens and the second lens, and the phase thereof is set appropriately, whereby the first lens. And chromatic aberration generated in the second lens is reduced.
[0028]
The diffractive optical element in the present embodiment is binary-manufactured by a lithographic technique that is a holographic optical element (HOE) manufacturing technique. The diffractive optical element may be made of binary optics (BINARY OPTICS). In this case, in order to further increase the diffraction efficiency, a saw-like shape called a kinoform may be used. Moreover, you may manufacture by shaping | molding by the direction manufactured by these methods.
[0029]
The shape of the diffractive optical element in the present embodiment is such that φ (h) = 2π / when the phase coefficient is C2i reference wavelength (d line) is λ, the distance from the optical axis is h, and the phase is φ (h). λ (C2 ・ h 2 + C4 ・ h 4 + C6 ・ h 6 +… C2i ・ h 2i )
It is represented by the formula of
[0030]
The paraxial refractive power and chromatic aberration with respect to the reference wavelength are controlled by changing the above-described phase coefficient C2. Further, the coefficient of the higher order term after the phase coefficient C4 obtains an effect similar to that of an aspherical surface with respect to the change in the refractive power with respect to the change in the incident light height of the diffractive optical element surface, and at the same time the reference wavelength according to the change in the light height. The chromatic aberration is controlled.
[0031]
In the present invention, when the secondary phase coefficient of the first lens is C21, the secondary phase coefficient of the second lens is C22, and the focal length of the entire system is ft,
1.0 × 10 -3 <Σ | C21 · f1 2 + C22 · f2 2 | / ft <2.0 × 10 -2 (2)
It is better to be in the range.
[0032]
If the lower limit of the conditional expression is exceeded, the correction of chromatic aberration will be insufficient, and conversely if it exceeds the upper limit, it will become excessive and the chromatic aberration will deteriorate.
[0033]
The diffractive optical element may be provided on the image surface side face of the first lens as Numerical Examples 1 and 3. Further, as in Numerical Example 2, it may be provided on the object side surface of the second lens . In addition, if the lens is provided on both the first and second lenses as in Reference Example 1, the aberration can be corrected more favorably. If a plastic lens is used as in Numerical Example 3, the entire optical system can be reduced in weight.
[0034]
Next, numerical examples of the converter lens of the present invention and the photographing lens M on which the converter lens is mounted will be shown. In 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 spacing in order from the object side, and ni and νi are the i-th lens in order from the object side. The refractive index and Abbe number of the glass. Table 1 shows the relationship between the above-described conditional expressions and numerical examples.
[0035]
The aspherical shape is the X axis in the optical axis direction, the Y axis in the direction perpendicular to the optical axis, the light traveling direction is positive, R is the paraxial radius of curvature, and K, B, C, D, E, and F are the aspheric coefficients. When
It is expressed by the following formula. “D-0X” means “10 −X ”.
[0036]
[Expression 1]
Example 1 1.33 times
r 1 = 40.871 d 1 = 9.50 n 1 = 1.51633 ν 1 = 64.2
* r 2 = -125.482 d 2 = 9.53
r 3 = -59.831 d 3 = 1.80 n 2 = 1.51633 ν 2 = 64.2
r 4 = 38.376
r 2 surface (diffractive surface) C2 = -1.32663 × 10 -4 C4 = -2.62248 × 10 -8
Example 2 1.29 times
r 1 = 41.203 d 1 = 9.50 n 1 = 1.48749 ν 1 = 70.2
r 2 = -83.303 d 2 = 7.97
* r 3 = -50.684 d 3 = 1.80 n 2 = 1.51633 ν 2 = 64.2
r 4 = 42.850
r 3 plane (diffractive surface) C2 = -7.90734 × 10 -5 C4 = -7.79424 × 10 -8
Reference Example 1 1.75 times
r 1 = 38.506 d 1 = 12.00 n 1 = 1.51633 ν 1 = 64.2
* r 2 = -2033.783 d 2 = 20.77
* r 3 = -103.091 d 3 = 1.80 n 2 = 1.69680 ν 2 = 55.5
r 4 = 42.144
r 2 surface (diffractive surface) C2 = -7.83985 × 10 -4 C4 = 2.29230 × 10 -7
r 3 surface (diffractive surface) C2 = 1.42721 × 10 -3 C4 = -1.10013 × 10 -6
Example 3 1.33 times
r 1 = 39.458 d 1 = 9.50 n 1 = 1.49171 ν 1 = 57.4
* r 2 = -115.271 d 2 = 9.52
r 3 = -55.654 d 3 = 1.80 n 2 = 1.49171 ν 2 = 57.4
r 4 = 37.122
r 2 surface (diffractive surface) C2 = -1.50965 × 10 -4 C4 = -3.11922 × 10 -8
Main lens system f = 64.09166
r 1 = 48.324 d 1 = 1.30 n 1 = 1.84666 ν 1 = 23.8
r 2 = 25.164 d 2 = 5.70 n 2 = 1.60311 ν 2 = 60.6
r 3 = -210.564 d 3 = 0.17
r 4 = 21.166 d 4 = 3.10 n 3 = 1.69680 ν 3 = 55.5
r 5 = 51.698 d 5 = 21.33
r 6 = 53.276 d 6 = 0.65 n 4 = 1.77250 ν 4 = 49.6
r 7 = 5.383 d 7 = 2.65
r 8 = -12.927 d 8 = 0.60 n 5 = 1.69680 ν 5 = 55.5
r 9 = 12.927 d 9 = 0.85
r10 = 12.407 d10 = 1.55 n 6 = 1.84666 ν 6 = 23.8
r11 = 84.497 d11 = 1.30
r12 = (Aperture) d12 = 1.20
* r13 = 7.654 d13 = 3.40 n 7 = 1.58313 ν 7 = 59.4
* r14 = 104.107 d14 = 0.20
r15 = 10.242 d15 = 0.60 n 8 = 1.84666 ν 8 = 23.8
r16 = 6.539 d16 = 1.59
r17 = 30.954 d17 = 1.60 n 9 = 1.51633 ν 9 = 64.1
r18 = -30.954 d18 = 1.70
r19 = ∞ d19 = 7.50
r20 = 12.613 d20 = 2.50 n10 = 1.60311 ν10 = 60.6
r21 = -12.613 d21 = 0.50 n11 = 1.84666 ν11 = 23.8
r22 = -33.464 d22 = 3.00
r23 = ∞ d23 = 3.69 n12 = 1.51633 ν12 = 64.1
r24 = ∞
r13 surface (aspherical surface) K = -2.58314 B = -2.58314 C = 5.75642 × 10 -4
D = -6.74713 × 10 -6 E = 7.18668 × 10 -8
r14 surface (aspherical surface) K = 1.80987 × 10 2 B = 7.32779 × 10 -5
C = -4.13717 × 10 -6
[0037]
[Table 1]
[0038]
【The invention's effect】
As described above, according to the present invention, the first lens and the second lens are provided, and a diffractive optical surface is introduced into at least one of the lens surfaces. By combining the canceling effect, it is possible to achieve a converter lens that enhances the correction effect of chromatic aberration particularly near the telephoto end.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram when the converter lens of Numerical Example 1 according to the present invention is mounted forward on the optical axis of a photographing lens. FIG. 2 is a schematic diagram illustrating the converter lens of Numerical Example 1 according to the present invention on the optical axis of a photographing lens. Aberration diagram when mounted forward [FIG. 3] Aberration diagram when the converter lens of Numerical Example 2 of the present invention is mounted forward on the optical axis of the photographing lens [FIG. 4] Converter lens of Reference Example 1 of the present invention FIG. 5 is an aberration diagram when the converter lens according to Numerical Example 3 of the present invention is attached to the front of the photographing lens on the optical axis. FIG. illustration of a diffractive optical element according to the illustration of a wavelength dependency of the diffractive optical element according to a reference example of the diffraction diagram of the optical element 7 of the present invention according to a reference example 8 the invention [9] Wavelength dependence characteristics of the diffractive optical element according to the present invention Illustration of a diffractive optical element according to the illustration [10] The present invention Description of Reference Numerals]
C converter lens M photographing lens L1 first lens L2 second lens d d line g g line ΔS sagittal image plane ΔM meridional image plane
Claims (5)
１．２５＜｜ｆ１／ｆ２｜＜２．５
なる条件を満足することを特徴とするコンバーターレンズ。A converter lens that is mounted on the object side of a lens system and changes the focal length of the entire lens system, and has a two-layer structure made of a positive first lens, a negative second lens, and materials having different dispersions. The first lens and the second lens are arranged in order from the object side, and the diffractive optical element is formed on one lens surface of the first lens or the second lens. When the focal lengths of the first lens and the second lens are f1 and f2, respectively.
1.25 <| f1 / f2 | <2.5
A converter lens characterized by satisfying the following conditions.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP36854198A JP4298028B2 (en) | 1998-12-09 | 1998-12-09 | Converter lens |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP36854198A JP4298028B2 (en) | 1998-12-09 | 1998-12-09 | Converter lens |
Publications (3)
| Publication Number | Publication Date |
|---|---|
| JP2000171708A JP2000171708A (en) | 2000-06-23 |
| JP2000171708A5 JP2000171708A5 (en) | 2006-01-26 |
| JP4298028B2 true JP4298028B2 (en) | 2009-07-15 |
Family
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Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP36854198A Expired - Fee Related JP4298028B2 (en) | 1998-12-09 | 1998-12-09 | Converter lens |
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| Country | Link |
|---|---|
| JP (1) | JP4298028B2 (en) |
Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP4650715B2 (en) * | 2002-12-24 | 2011-03-16 | 株式会社ニコン | Front teleconverter lens |
| US10955644B2 (en) | 2017-12-25 | 2021-03-23 | Olympus Corporation | Zoom optical system, image pickup optical system, and image pickup apparatus using the same |
-
1998
- 1998-12-09 JP JP36854198A patent/JP4298028B2/en not_active Expired - Fee Related
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| JP2000171708A (en) | 2000-06-23 |
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