JP3657467B2 - Plastic diffraction molded lens and optical system using the lens - Google Patents

Description

本式の右辺のうち、第１〜第２行は非球面基盤を表わし、第３行及び第４行は、回折格子成分を表わす。特に、第４行は、上述した輪帯形成時（設計時）のリセットに対応している。また、使用されている符号については次の通りである。
【００６５】
ｃ；面頂における非球面基盤の曲率
ｋ；円錐係数
Ａ₄ 、Ａ₆ 、Ａ₈ ・・・；各々４次、６次、８次・・・の非球面係数
ａ₁ 、ａ₂ 、ａ₃ ・・・ａ₁₀；前述した光路差関数（級数表現）の係数
λ_d ；前出のλ_d と同じく、回折構造の設計波長
ｎ_d ：設計波長λ_d における回折構造に使用される光学材料の屈折率
δ_rF1 、δ_rF2 、δ_rF3 ・・・；０または１の値をとるｒの関数。添字をｒＦｓ（ｓ＝１、２、３・・・）とした時、０≦ｒ＜Ｆｓでは値０をとり、ｒ≧Ｆｓでは値１をとる。なお、ここでＦｓは光軸側から数えてｓ番目の輪帯が始まる段差位置を表わしている。
【００６６】
以下の各実施例１〜３においては、回折構造の設計波長λ_d を５５０ｎｍ（Ｈｇの発光スペクトル線であるｅ線の波長、５４６．０７ｎｍにほぼ対応）とした。レンズの材質は、上述した通り、回折構造部分を含めてポリカーボネート（屈折率；１．５８７７２）である。従って、前記（３）式の第４行の｛｝内部分にこれら数値を入れて計算すると、λ_d ／（ｎ_d −１）＝９３５．８ｎｍとなる。これは回折溝の深さ（基盤からのずれ）を表わしている。
【００６７】
また、データ記述で使用されている諸符号は慣例にならったものであり、その意味は次の通りである。
ｆ；光学系全体の焦点距離（ｍｍ）
Ｆ／Ｎｏ；Ｆナンバー
ω；半画角
ｃ₁ 、ｃ₂ ・・・；各レンズ面の曲率（ｍｍ^-1）
ｄ₁ 、ｄ₂ ・・・；各レンズ面間の間隔（ｍｍ）
ｎ_d1、ｎ_d2・・・：各レンズ材料の屈折率（Ｈｅのｄ線＝５８７．５６ｎｍでの値を使用）
ν_d1、ν_d2・・・：各レンズ材料のアッベ数で、非球面係数及び光路差関数の係数については、前述の定義に従うものとする。
【００６８】

なお、本実施例１において、図９中に示した絞りＩＲが第１面（ｃ₁ ）に対応する。そして、レンズＬＳ１の物体側の面Ｋ１が第２面（ｃ₂ ）、像面側の面Ｊ１が第３面（ｃ₃ ）にそれぞれ対応する。更に、ガラス板Ｅの物体側の面が第４面（ｃ₄ ）、像面側の面が第５面（ｃ₅ ）に各々対応する。
【００６９】
従って、絞りＩＲとレンズＬＳ１の第１面Ｋ１（物体側の面ｃ₂ ）の間の距離がｄ₁ となる。また、レンズＬＳ１の第１面Ｋ１（物体側の面ｃ₂ ）と同レンズＬＳ１の第２面Ｊ１（像面側の面ｃ₃ ）の間の距離がｄ₂ となり、レンズＬＳ１の第２面Ｊ１（像面側の面ｃ₃ ）とガラス板Ｅの物体側の面との間の距離がｄ₃ となる。そして、ガラス板Ｅの物体側の面（ｃ₄ ）と像面側の面（ｃ₅ ）との間の距離（ここではガラス板の厚さ）がｄ₄ となり、ガラス板Ｅの像面側の面（ｃ₅ ）と像面Ｇの間の距離がｄ₅ となる。
【００７０】

本実施例におけるこれら諸値と図１０に示した配置との対応関係は、実施例１の場合と同様である。
即ち、絞りＩＲが第１面（ｃ₁ ）に対応する。そして、レンズＬＳ２の物体側の面Ｋ２が第２面（ｃ₂ ）、像面側の面Ｊ２が第３面（ｃ₃ ）にそれぞれ対応する。更に、ガラス板Ｅの物体側の面が第４面（ｃ₄ ）、像面側の面が第５面（ｃ₅ ）に各々対応する。
【００７１】
従って、絞りＩＲとレンズＬＳ２の第１面Ｋ２（物体側の面ｃ₂ ）の間の距離がｄ₁ となる。また、レンズＬＳ２の第１面Ｋ２（物体側の面ｃ₂ ）と同レンズＬＳ２の第２面Ｊ２（像面側の面ｃ₃ ）の間の距離がｄ₂ となり、レンズＬＳ２の第２面Ｊ２（像面側の面ｃ₃ ）とガラス板Ｅの物体側の面との間の距離がｄ₃ となる。そして、ガラス板Ｅの物体側の面（ｃ₄ ）と像面側の面（ｃ₅ ）との間の距離（ここではガラス板の厚さ）がｄ₄ となり、ガラス板Ｅの像面側の面（ｃ₅ ）と像面Ｇの間の距離がｄ₅ となる。
【００７２】

これら諸値と図１１に示した配置との対応関係は、実施例１、２の場合と同様の基本ルールに基づいて定められているが、ガラス板ＨがレンズＬＳ３の手前側（物体側）に配置されているため、若干の注意が必要である。
【００７３】
先ず、絞りＩＲが第１面（ｃ₁ ）に対応し、ガラス板Ｈの物体側の面が第２面（ｃ₂ ）に対応する。面ｃ₁ ｃ₂ 間の距離がｄ₁ となる。ここで、絞りＩＲの面はガラス板Ｈの物体側の面とは別の面として扱われていることに注意が必要である。但し、上記したように、本例における距離ｄ₁ は０である。
【００７４】
次に、ガラス板Ｈの像面側の面が第３面（ｃ₃ ）、レンズＬＳ３の物体側の面Ｋ３が第４面（ｃ₄ ）、像面側の面Ｊ３が第５面（ｃ₅ ）にそれぞれ対応する。更に、ガラス板Ｅの物体側の面が第６面（ｃ₆ ）、像面側の面が第７面（ｃ₇ ）に各々対応する。
【００７５】
従って、ｄ₂ はガラス板Ｈの厚さであり、ｄ₃ はガラス板Ｈの像面側の面（ｃ₃ ）とレンズＬＳ３の第１面Ｋ３（物体側の面ｃ₄ ）との間の距離となる。また、レンズＬＳ３の第１面Ｋ３（物体側の面ｃ₄ ）と同レンズＬＳ３の第２面Ｊ３（像面側の面ｃ₅ ）の間の距離がｄ₄ となる。
【００７６】
同様に、レンズＬＳ３の第２面Ｊ３（像面側の面ｃ₅ ）とガラス板Ｅの物体側の面との間の距離がｄ₅ となり、同ガラス板Ｅの厚さがｄ₆ となる。そして、ガラス板Ｅの像面側の面（ｃ₇ ）と像面Ｇの間の距離がｄ₇ となる。
【００７７】
【発明の効果】
以上説明したように、本発明に従えば、射出成形で代表されるレプリカ法を適用しても回折溝形状の転写不良を生じ難いプラスチック製の回折成形レンズ並びに該レンズを有利な形態で用いた光学系が提供される。即ち、回折溝形成部の形状に簡単な変更を施すことで、凸面上の回折溝で特に生じ易かった溝形状の乱れを解消し、凸面の基盤上に輪帯状の回折溝が規則正しく形成されたプラスチック製回折成形レンズを安価に提供出来る。また、凸面上に回折溝を備えた製造容易な正のプラスチック製回折成形レンズを単葉で配置した簡単で特性の優れた光学系を提供することが出来る。
【図面の簡単な説明】
【図１】 同心円環状の回折溝を凸面に備えた従来の回折成形レンズを射出成形によって製造する際の樹脂の流れを、（ａ）→（ｂ）→（ｃ）→（ｄ）と順を追って断面図で示したものである。
【図２】 本発明の特徴を備えたプラスチック製回折成形レンズを製造する際に使用される金型（要部部材）の一例を示した図で、（ａ）は（ｂ）に斜視図で示した金型（要部部材）の上面図である。
【図３】 図１と同様の形式で、金型部材２０、４０を用いて回折成形レンズを射出成形によって製造する際の樹脂の流れを、（ａ）→（ｂ）→（ｃ）→（ｄ）と順を追って断面図で示したものである。
【図４】 凸条部の形成形態の１例について説明する図である。
【図５】 凸条部の形成形態の別の例について説明する図である。
【図６】 凸条部の形成形態の参考例について説明する図である。
【図７】 １本の凸条部を有する回折成形レンズの例を表わした図である。
【図８】 ４本の凸条部を有する回折成形レンズの例を表わした図である。
【図９】 改良された回折成形レンズを配置した光学系の例を説明する図である。
【図１０】 改良された回折成形レンズを配置した光学系の別の１例を説明する図である。
【図１１】 改良された別の回折成形レンズを配置した光学系の１例を説明する図である。
【符号の説明】
１ 金型
２ キャビティ
３ 回折溝転写部
４、４１ 緩い凹面
１０ 溶融樹脂
１１ 溶融樹脂の流れの先頭部
１２ 回折溝転写部に近接した溶融樹脂
１３ 回折溝転写部と溶融樹脂の間の隙間（未充填部）
２０、４０、Ｍ、Ｎ、Ｔ 金型部材
２１ 回折溝転写部
２５、ＣＶ キャビティ
３１、３２、３３、ＧＰ ガス抜き用の溝
Ｅ、Ｈ ガラス板
Ｇ 像面
ＩＲ 絞り
Ｊ１、Ｊ２、Ｊ３ 回折面
Ｋ１、Ｋ２ 緩い凸面
Ｋ３ 緩い凹面
Ｌ１、Ｌ２、ＬＳ１、ＬＳ２、ＬＳ３ 回折成形レンズ
Ｑ 底部Ｒが乗る凹面
Ｒ 回折溝転写部の溝
Ｗ 凹面Ｑ（破線）から一定の深さで凹んだ線状部分
Ｙ 深さが外縁部へ向かって深まるように形成された線状部分[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a plastic diffraction molded lens, in particular, a chromatic aberration corrected diffraction molded lens, in which an annular diffraction groove is formed on a convex substrate, and an optical system using the lens. The diffraction shaping lens and the optical system according to the present invention are suitably used for an imaging optical system having a single lens configuration of a small camera using a solid-state imaging device such as a CCD or CMOS.
[0002]
[Prior art]
For example, in a small camera using a solid-state imaging device such as a CCD or CMOS, it is well known that a positive lens having a chromatic aberration correcting function by forming an annular diffraction groove on a convex substrate is used as an imaging lens. It has become. Such a lens is called a chromatic aberration correction lens, and has an advantage that a single lens can easily form an imaging system having a chromatic aberration correction function. It is known that by adopting plastic as a material, it is possible to apply a plastic molding technique by a replica method typified by injection molding, and to supply a product with a stable performance in large quantities at a low cost.
[0003]
By the way, in a lens that corrects chromatic aberration by utilizing the diffraction effect of an annular diffraction groove like a chromatic aberration correction lens, it is possible to maintain the performance by giving the diffraction groove a shape as close to the designed shape as possible. It becomes important in the above. In other words, a diffractive molded lens in which a diffractive groove different from the shape intended by the design is generated, it is inevitable that performance degradation such as generation of multiple focal points is generated by generating diffracted light of an unnecessary order.
[0004]
Therefore, sufficient attention is paid to the cavity shape of the mold used for the injection molding of the diffractive molded lens so as to have a high accuracy corresponding to the designed diffraction groove shape. However, in the conventional diffraction molded lens, even if the accuracy of the cavity shape is ensured, it has been extremely difficult to obtain a product faithfully copying the cavity shape groove shape.
[0005]
Such difficulty is caused by the fact that the diffraction grooves formed on the surface of the lens have a concentric annular closed structure. This will be described with reference to FIG. FIG. 1 is a cross-sectional view showing the flow of resin when a conventional diffractive lens having a concentric annular diffraction groove on its convex surface is manufactured by injection molding.
[0006]
(A) represents a state immediately before the leading portion 11 of the molten resin 10 is injected into the cavity 2 of the mold 1. The cavity 2 has a diffraction groove transfer portion 3 for forming concentric annular diffraction grooves on the convex surface of the lens. The inner surface facing the diffraction groove transfer portion 3 across the cavity 2 is a loose concave surface 4. The diffraction groove transfer portion 3 is formed based on a concave surface having a larger curvature than the loose concave surface 4. Reference symbol A is used as a gas escape route to be removed as the leading portion 11 of the molten resin 10 enters the cavity 2 at the boundary between a plurality of members constituting the mold 1.
[0007]
The gas to be excluded includes gas contained in the molten resin 10 in addition to the gas (air) present in the cavity 2 before the resin injection. In general, such a gas escape path is called a “gas vent” or simply “gas vent”.
[0008]
By injection, the molten resin 10 is injected into the cavity as shown in FIGS. 1B, 1C, and 1D. FIG. 1D shows a state immediately before the completion of the injection of the molten resin 10. In this process, most of the gas in the cavity 2 is discharged to the outside through the gas vent passage A secured between the members of the mold 1. The gas occupying the gap 14 remaining around the top portion 11 of the molten resin 10 is also discharged through the gas vent path A when the injection is completed.
[0009]
However, in the diffraction groove transfer part 3, a phenomenon occurs in which part of the gas is trapped in the gap 13 in each diffraction groove of the diffraction groove transfer part 3. As shown in FIG. 1 (d), when the molten resin 10 approaches the diffraction groove transfer portion 3 and tries to enter the annular groove corresponding to each diffraction groove, the diffraction groove transfer portion is already present. This is because 3 is in a state covered with the molten resin 10 and the gas escape route is cut off.
[0010]
The gas confined in the gap 13 (air and gas generated from the high-temperature molten resin 10) hinders injection of the molten resin 10 into a sufficient groove, and the groove shape is significantly disturbed due to poor transfer. As a result, a diffractive molded lens having a groove shape as designed (as in the mold) cannot be obtained. In particular, in the case of a diffractive molded lens, the disorder of the groove shape generates diffracted light of an unnecessary order and greatly deteriorates the performance such as the chromatic aberration correction function.
[0011]
Such a phenomenon tends to be prominent when a diffraction groove is formed on a convex surface as in this example. This is because compared with the case where the diffraction grooves are formed on the concave surface or on the flat surface, the molten resin closes the concave portions of the diffraction groove transfer portion of the mold, and it is easy to leave the gas whose escape path is cut off. It seems to be due to this.
[0012]
For the above reasons, the conventional plastic diffractive molded lens is designed to have a diffraction groove having a regular shape in design, but actually has a diffraction groove having a large distance from the design shape. I had to accept it.
[0013]
In addition, although the technique of giving the shape and dimension which anticipated the transfer defect by gas confinement beforehand to the diffraction groove transfer part 3 of the metal mold | die 1 is utilized, it is difficult to implement | achieve the intended groove shape stably.
[0014]
As a matter of course, the performance of an optical system using such a conventional plastic diffractive molded lens as an imaging optical element has problems such as degradation of imaging characteristics due to multiple focal points.
[0015]
[Problems to be solved by the invention]
Therefore, a basic object of the present invention is to make a plastic diffraction molded lens that does not easily cause a transfer failure of a diffraction groove shape even when a replica method represented by injection molding is applied, and an optical device using the lens in an advantageous form. It is to provide a system to overcome the problems of the prior art.
[0016]
From another point of view, the object of the present invention is to provide a simple change to the shape of the diffractive groove forming portion, thereby eliminating the irregularity of the groove shape that is particularly likely to occur in the diffractive groove on the convex surface. Another object of the present invention is to provide a plastic diffractive molded lens in which ring-shaped diffraction grooves are regularly formed and an optical system using the lens in an advantageous form.
[0017]
From another point of view, the present invention is to provide a positive plastic diffractive molded lens having a diffractive groove on a convex surface and an optical system using the lens in an advantageous form.
[0018]
[Means for Solving the Problems]
  First, in order to solve the above technical problem, the present invention relates to a plastic diffractive molded lens having at least one convex surface, in which a diffractive annular zone structure is formed on the convex surface. A thin ridge to cross the structureThe top portion is formed on the base surface or parallel to the base surface and outside the base surface.Propose to provide.
[0019]
  That is,FirstBy providing the thin ridges so as to cross the annular structure, a gas venting path can be easily secured to the diffraction groove transfer part when injection molding is applied.In addition, the plastic diffractive molded lens can be easily manufactured, and the diffraction groove shapeThere is no disturbance, and it becomes easy to suppress the generation of diffracted light of unnecessary order. A diffractive annular zone structure is typically formed for chromatic aberration correction.
[0020]
  Furthermore, in the present invention, regarding the formation form of the above-mentioned ridge portion, “the top portion is formed on the base surface or parallel to the base surface and outside the base surface. ”Is imposed.
[0021]
A typical application object of the present invention is a so-called chromatic aberration correcting diffractive lens, that is, a lens having a diffraction ring structure for correcting chromatic aberration.
Theoretically speaking, providing a thin ridge so as to cross the annular structure gives the portion different optical characteristics from other portions, and the performance of the chromatic aberration correction function and the like is lowered. However, this problem does not lose the significance of the present invention.
[0022]
This is because the thin ridges formed so as to cross the annular structure may be very small in size (width and height enough to allow degassing). This is because, as viewed from the entire convex surface, it remains extremely local, whereas the diffraction groove can easily achieve the designed groove shape in a wide portion excluding the local portion where the ridge portion is formed.
[0023]
In the lens having the conventional shape, although the performance does not change due to the formation of the ridge portion, the shape of the diffraction groove responsible for the chromatic aberration correction function is disturbed apart from the design. As understood from the above description, the confinement of the gas that causes the disturbance of the shape of the diffraction groove is not of a nature that occurs locally.
[0024]
Therefore, even if the change in optical characteristics due to the formation of convex portions that can occur theoretically is taken into consideration, there are more merits due to normalization of the shape of the diffraction groove (realization of the shape as designed).
[0025]
Next, the present invention proposes an optical system using the above-described diffractive molded lens in a form in which the influence of the performance change due to the formation of the ridge is reduced.
[0026]
  The optical system according to the present invention comprises a single piecePlasticA positive lens and a stop are included, and the stop is disposed closer to the object side than the positive lens. As a positive lens, a plastic diffractive molding that has a convex surface on the image surface side as a base surface, a diffraction ring zone structure is formed on the convex surface, and a thin ridge is provided so as to cross the ring zone structure A lens is used.
[0027]
  A diffractive annular zone structure is typically formed for chromatic aberration correction. This plastic diffractive molded lensas,Formation form of the above-mentioned ridgesThose that meet the conditions for.
[0028]
In the optical system of the present invention, since the diffractive structure is provided on the convex surface, a problem lens surface can be obtained by causing the convex surface to bear all or most of the refractive power (positive as a whole; condensing action) of the lens. The imaging light beam can be made to be a substantially parallel light beam (here, a convex surface provided with a diffractive structure).
[0029]
In addition, it is advantageous to dispose the lens so that the convex surface comes to the image surface side from the viewpoint of preventing the diffraction structure from being damaged, dust adhesion, foreign matter jamming, etc. in the camera assembly process or the like.
[0030]
The ridges that cross the diffractive structure are typically formed in the radial direction of the convex surface so as to cross the annular zone substantially at a right angle. In addition, the number of protrusions formed is appropriately selected as necessary. Generally, if the number is increased, degassing at the time of injection molding becomes easy, but the influence on the optical characteristics also increases. Therefore, it is preferable to determine the design in consideration of the balance between the two. When a plurality of ridges are formed, they may be formed radially in a form that is not concentrated and distributed in the circumferential direction.
[0031]
DETAILED DESCRIPTION OF THE INVENTION
FIGS. 2A and 2B are views showing an example of a mold (main part member) used in manufacturing a plastic diffractive molded lens having the characteristics of the present invention. Fig.2 (a) is a top view of the metal mold | die (main part member) shown by the perspective view in FIG.2 (b).
[0032]
Referring to FIGS. 2A and 2B, the mold member 20 includes a diffraction groove transfer portion 21, and three gas venting grooves 31, 32, and 33 are formed in the diffraction groove transfer portion 21. Has been. As can be understood from the partial extraction enlarged view (circle C) illustrating the vicinity of the groove 33 exemplarily, the degassing grooves 31, 32, 33 divide each groove of the diffraction groove transfer portion 21 (for example, 22a and 22b), one end of which extends to the outer edge of the mold member 20.
[0033]
When injection molding is performed using such a mold member 20, naturally, the degassing grooves 31, 32, and 33 give convex portions to the molded product by transfer. In addition, a large number of diffraction structure transfer grooves 22a and 22b give a large number of flanges (diffraction grooves) to the molded product by transfer. The protruding portion is formed so as to cross a large number of flanges (diffraction grooves).
[0034]
What is important here is the fact that it is possible to use a mold member having degassing grooves 31, 32, 33 by allowing such a convex portion on the molded lens. As a result, the transfer defect related to the formation of the diffraction groove is eliminated, and a diffraction molded lens having a groove shape as designed is realized.
[0035]
FIG. 3 is a cross-sectional view showing the flow of resin when a diffraction molding lens is manufactured by injection molding using the mold member 20 in the same manner as FIG.
[0036]
(A) represents a state immediately before the leading portion 11 of the molten resin 10 is injected into the cavity 25 between the mold members 20 and 40. The cavity 25 has a diffraction groove transfer portion 21 for forming a concentric annular diffraction groove on the convex surface of the lens. The inner surface facing the diffraction groove transfer portion 21 across the cavity 25 is a loose concave surface 41. The diffraction groove transfer portion 21 is formed based on a concave surface having a larger curvature than the loose concave surface 41. Further, in the above-described form (see FIG. 2), gas venting grooves 31, 32, 33 are provided that cross in the radial direction.
[0037]
By injection, the molten resin 10 is injected into the cavity 25 as shown in FIGS. 3 (b), 3 (c), and 3 (d). FIG. 3D shows a state immediately before the injection of the molten resin 10 is completed. In this process, the gas occupying the gap 26 remaining around the top portion 11 of the molten resin 10 is discharged through the gas venting path between the mold members 20 and 40 when the injection is completed.
[0038]
On the other hand, in the diffraction groove transfer portion 21, a part of gas tends to remain in the gaps in the diffraction grooves of the diffraction groove transfer portion 21. This is because when the molten resin 10 approaches the diffraction groove transfer portion 21 and attempts to enter an annular (exactly arc-shaped) groove corresponding to each diffraction groove, the diffraction groove transfer portion 21 is made of the molten resin 10. It is because it is in a covered state.
[0039]
However, unlike the case described with reference to FIG. 1, the diffraction groove transfer portion 21 is provided with degassing grooves 31, 32, 33 that traverse in the radial direction. It escapes from the inside of the annular (exactly arcuate) groove and is discharged to the outside through the grooves 31, 32 and 33.
[0040]
Accordingly, sufficient injection of the molten resin 10 into the groove for transferring the diffraction groove is achieved, and the shape disturbance due to transfer failure is avoided. As a result, a diffraction molded lens having a groove shape as designed can be obtained. Unnecessary orders of diffracted light are not generated, and performance such as a chromatic aberration correction function is maintained.
[0041]
Such venting is sufficiently ensured even when a diffraction groove is formed on the convex surface as in this example. Therefore, formation of a diffractive structure on a convex surface, which has been difficult in the past, can be easily realized.
[0042]
When the mold member 20 shown in FIG. 2 is used, a diffractive molded lens having three convex portions corresponding to the positions of the gas venting grooves 31, 32, 33 is obtained. If the position and number of the gas vent grooves are changed, diffractive molded lenses having convex strips at various positions can be obtained accordingly.
[0043]
For example, if one groove for degassing is provided, a diffraction molded lens L1 as shown in FIG. 7 is obtained. The diffractive molded lens L1 has a convex surface as a base surface, and a diffractive surface DF is formed thereon. The diffractive surface DF is composed of a large number of concentric annular (exactly concentric arcs) diffraction grooves, and one ridge portion PR is formed so as to cross them substantially at a right angle.
[0044]
Further, if the gas venting grooves are radially four, a diffractive molded lens L2 as shown in FIG. 8 can be obtained. The diffractive molded lens L2 has a convex surface as a base surface, and a diffractive surface DF is formed thereon. The diffractive surface DF is composed of a large number of concentric annular (exactly concentric arcs) diffraction grooves, and four protruding strips PR1 to PR4 are formed so as to cross them substantially at right angles. 7 and 8, S represents a convex portion corresponding to the resin injection port side (gate side).
[0045]
  Next, the form of protrusionsExample4 to 6TheBrowseTheoryLight up.Of these figures, FIG. 6 shows a reference example. Also,4 to 6 are drawn as cross-sectional views with an enlarged enlarged view similar to FIG. 3 (d).
[0046]
First, FIG. 4 shows the most basic example. In this example, a part (linear portion) of the concave surface Q on which the bottom R of the groove of the diffraction groove transfer portion of the mold M forming the cavity CV rides forms the top of the gas venting groove GP. The concave surface Q corresponds to a convex surface that is a base surface of a lens obtained by molding. Therefore, the convex strip portion of the diffraction molded lens obtained in this example is formed so that the top portion thereof is located on the base surface of the lens.
[0047]
Next, FIG. 5 shows a case formed so that the top of the ridge is parallel to the base surface and located outside the base surface. That is, the linear portion W that is recessed at a certain depth from the concave surface Q (broken line) on which the groove bottom R of the diffraction groove transfer portion of the mold N forming the cavity CV is formed forms the top of the groove GP. Since the concave surface Q corresponds to a convex surface that is a base surface of a lens obtained by molding, the convex strip portion of the molded lens forms a ridge that protrudes from the base surface at a certain height.
[0048]
  Shown as a reference exampleIn FIG. 6, the linear portion Y formed so that the depth from the concave surface Q (broken line) on which the groove bottom portion R of the diffraction groove transfer portion of the mold T that forms the cavity CV rides increases toward the outer edge portion. The top of the groove GP is formed. Since the concave surface Q corresponds to the convex surface that becomes the base surface of the lens obtained by molding, the convex strip portion of the molded lens is formed so that the height from the base surface tends to increase as it approaches the outer edge of the convex surface. Will be.
[0049]
Examples of the optical system in which the diffractive lens having the shape as described above is arranged as a single leaf are shown in FIGS. In the figure, ray tracing lines are written.
[0050]
9 and 10, the lenses LS1 and LS2 have convex surfaces J1 and J2 with concentrated positive refractive power and loose convex surfaces K1 and K2 with a slight positive refractive power, respectively. However, the degree of concentration of refractive power is stronger in FIG. 9 than in FIG.
[0051]
Although not shown, on the convex surfaces (diffractive surfaces) J1 and J2, a large number of concentric annular (exactly concentric arcs) diffraction grooves formed according to a specified design are formed. One or several ridges are formed on the convex surfaces J1 and J2 so as to cross these. Any form described above may be adopted for the ridges.
[0052]
The stop IR is disposed on the object side of the lenses LS1 and LS2, and is oriented so that the diffraction surfaces J1 and J2 face the image plane G side. For example, a CCD array is arranged at the position of the image plane G. The glass plate E corresponds to, for example, a window of a CCD array.
[0053]
In the optical system shown in FIGS. 9 and 10, most of the refractive power (positive as a whole; condensing action) of the lens LS1 or LS2 is given to the diffractive surface J1 or J2. The image light beam becomes a substantially parallel light beam, and the influence of the characteristic change due to the provision of the ridge portion is suppressed to be very small.
[0054]
Further, since the lenses LS1 and LS2 are arranged so that the convex surface comes to the image plane G side, it is advantageous from the viewpoint of preventing damage to the diffractive structure, dust adhesion, foreign matter jamming, etc. in the camera assembly process. is there.
[0055]
Next, in FIG. 11, the lens LS3 constitutes a meniscus lens. That is, it has a convex surface J3 that concentrates positive refractive power and a loose concave surface K3 that has small negative refractive power. Although not shown, on the convex surface (diffractive surface) J3, a large number of concentric annular (exactly concentric arc) diffraction grooves formed in accordance with a designated design are formed. And 1 thru | or several protrusions are formed on the convex surface J3 so that these may be crossed. Any form described above may be adopted for the ridges.
[0056]
The diffractive surface J3 is oriented so as to face the image plane G side. For example, a CCD array is arranged at the position of the image plane G. The glass plate E corresponds to, for example, a window of a CCD array. Moreover, the glass plate H is corresponded to the protective window of the concave surface K3, for example. The diaphragm IR in this example is provided near the outer edge of the object-side surface of the glass plate H.
[0057]
Even in the optical system of this example, most of the refractive power (positive as a whole; condensing action) of the lens LS3 is given to the diffractive surface J3, so that the imaging light beam becomes a substantially parallel light beam on the diffractive surface J3. The influence of the characteristic change due to the provision of is kept very small. Further, since the lens LS3 is disposed so that the convex surface comes to the image plane G side, it is advantageous from the viewpoint of preventing damage to the diffractive structure, dust adhesion, foreign matter jamming, etc. in the camera assembly process.
[0058]
Finally, specific examples 1 to 3 including lens data will be described with respect to the optical systems shown in FIGS. The diffractive element (plastic molded lens having a diffractive structure provided on the convex surface) in these examples was manufactured by an injection molding method using a mold whose inner surface was processed corresponding to the diffraction groove. The mold was processed by a lathe using an ultra-precision diamond bite. The resin material was polycarbonate, the injection resin temperature was 280 ° C., and the mold temperature was 100 ° C.
[0059]
In each of Examples 1 to 3, the amount of change in optical path difference due to the diffractive structure of the diffractive optical element was determined using the phase function method. In the phase function method, the phase change of the wavefront due to the diffractive structure is expressed by a phase function defined by the following equation.
φ (r) = 2πΦ (r) / λ_d                           ... (1)
Φ (r) = a₁ r² + A₂ r^Four + A_Three r⁶ + ... + a_Tenr²⁰         ... (2)
Here, φ (r) is a phase function, Φ (r) is an optical path difference function, r is a radial distance of the optical element (r = 0 on the optical axis), a₁ ~ A_TenIs the coefficient of the optical path difference function and λ_d Represents the design wavelength of the diffraction element. The optical system was rotationally symmetric.
[0060]
Further, the diffractive surface of the diffractive optical element in each embodiment is a diffractive structure formed on an aspherical substrate, and the value of the optical path difference function of the diffractive structure, that is, the amount of deviation of the optical path difference from the aspherical substrate is , Design wavelength λ_d Integer multiple (−λ_d , -2λ_d -3λ_d The annular zone was designed and formed so as to reset the deviation amount of the optical path difference from the aspherical base to 0 at the position of r as shown in FIG.
[0061]
The reason why the ring zone structure can be designed and formed in this way is that the optical path difference is the design wavelength λ._d This is because the phase change due to the diffractive structure is an integral multiple of 2π, and the phase change of the wavefront with respect to the aspherical surface becomes equal to 0, as can be seen from the above equation.
[0062]
In each example, a sawtooth shape was adopted as a specific shape of the diffraction grating. Further, the change in the thickness of the element within each lattice pitch was made continuous. In addition, what made this thickness change correspond correctly to the phase change in the said grating | lattice pitch is called a kinoform. In order to suppress generation of unnecessary order diffracted light and to obtain high diffraction efficiency, it is desirable to bring the sawtooth shape closer to this kinoform.
[0063]
On the other hand, a shape in which the change in the thickness of the element within each lattice pitch is set in a binary step (2 levels, 4 levels, 8 levels,...) Is known, and is called a binary shape. In general, if the number of steps (number of levels) in a binary shape is small, it becomes difficult to achieve a good correspondence (approximation) with the phase change, and diffracted light of an unnecessary order is generated, and the diffraction efficiency is likely to decrease. Become. From such a viewpoint, when the binary shape is adopted, the number of stages is preferably 4 or more.
[0064]
Here, a definition formula that specifically describes the shape of the diffraction surface, which is commonly applied to each of the first to third embodiments in which the diffraction grating has a sawtooth shape, will be described.
The following formula (3) is adopted as a formula for expressing the shape of the diffractive surface. Here, the optical axis direction is the Z axis, and the radial distance (measured from the optical axis) perpendicular to the optical axis is r. Z (r) represents the position (Z coordinate value) of the diffraction surface at r.

Of the right side of this equation, the first and second rows represent the aspherical surface, and the third and fourth rows represent the diffraction grating components. In particular, the fourth row corresponds to the above-described reset at the time of ring zone formation (design time). Further, the codes used are as follows.
[0065]
c: Curvature of aspherical base at the top
k: cone coefficient
A_Four , A₆ , A₈ ... 4th, 6th, 8th ... aspherical coefficients
a₁ , A₂ , A_Three ... a_Ten; Coefficient of optical path difference function (series expression) described above
λ_d ; Λ mentioned above_d Same as diffractive structure design wavelength
n_d : Design wavelength λ_d Refractive index of optical materials used for diffractive structures in
δ_rF1 , Δ_rF2 , Δ_rF3 ... A function of r taking a value of 0 or 1. When the subscript is rFs (s = 1, 2, 3,...), 0 ≦ r <Fs takes value 0, and r ≧ Fs takes value 1. Here, Fs represents a step position where the s-th annular zone starts from the optical axis side.
[0066]
In each of the following Examples 1 to 3, the design wavelength λ of the diffractive structure_d Was 550 nm (corresponding approximately to the wavelength of e-line, which is an emission spectrum line of Hg, 546.07 nm). As described above, the material of the lens is polycarbonate (refractive index: 1.58772) including the diffraction structure portion. Therefore, when these numerical values are put in the part in {} of the fourth line of the above equation (3) and calculated, λ_d / (N_d -1) = 935.8 nm. This represents the depth of the diffraction groove (deviation from the substrate).
[0067]
Further, the various codes used in the data description are in accordance with the convention, and their meanings are as follows.
f: Focal length of the entire optical system (mm)
F / No; F number
ω: Half angle of view
c₁ , C₂ ... curvature of each lens surface (mm^-1)
d₁ , D₂ .... Distance between lens surfaces (mm)
n_d1, N_d2...: Refractive index of each lens material (He d line = 587.56 nm value is used)
ν_d1, Ν_d2...: Abbe number of each lens material, and the aspherical coefficient and the coefficient of the optical path difference function are as defined above.
[0068]

In the first embodiment, the diaphragm IR shown in FIG.₁ ). The object-side surface K1 of the lens LS1 is the second surface (c₂ ), The surface J1 on the image plane side is the third surface (c_Three ) Respectively. Furthermore, the object side surface of the glass plate E is the fourth surface (c_Four ), The image side surface is the fifth surface (c_Five ) Respectively.
[0069]
Accordingly, the iris IR and the first surface K1 of the lens LS1 (surface c on the object side)₂ ) Is d₁ It becomes. Further, the first surface K1 of the lens LS1 (surface c on the object side)₂ ) And the second surface J1 (image surface side surface c) of the lens LS1._Three ) Is d₂ The second surface J1 of the lens LS1 (surface c on the image plane side)_Three ) And the object-side surface of the glass plate E is d_Three It becomes. And the object side surface of the glass plate E (c_Four ) And the image side surface (c_Five ) (In this case, the thickness of the glass plate) is d_Four The surface on the image plane side of the glass plate E (c_Five ) And the image plane G is d_Five It becomes.
[0070]

The correspondence between these various values in the present embodiment and the arrangement shown in FIG. 10 is the same as in the first embodiment.
That is, the iris IR is the first surface (c₁ ). The object-side surface K2 of the lens LS2 is the second surface (c₂ ), The surface J2 on the image plane side is the third surface (c_Three ) Respectively. Furthermore, the object side surface of the glass plate E is the fourth surface (c_Four ), The image side surface is the fifth surface (c_Five ) Respectively.
[0071]
Accordingly, the diaphragm IR and the first surface K2 of the lens LS2 (object-side surface c)₂ ) Is d₁ It becomes. The first surface K2 of the lens LS2 (object-side surface c₂ ) And the second surface J2 (image surface side surface c) of the lens LS2_Three ) Is d₂ The second surface J2 of the lens LS2 (image surface side surface c)_Three ) And the object-side surface of the glass plate E is d_Three It becomes. And the object side surface of the glass plate E (c_Four ) And the image side surface (c_Five ) (In this case, the thickness of the glass plate) is d_Four The surface on the image plane side of the glass plate E (c_Five ) And the image plane G is d_Five It becomes.
[0072]

The correspondence relationship between these values and the arrangement shown in FIG. 11 is determined based on the same basic rules as in the first and second embodiments, but the glass plate H is on the front side (object side) of the lens LS3. Because it is arranged in, it needs some attention.
[0073]
First, the iris IR is the first surface (c₁ ), The object side surface of the glass plate H is the second surface (c₂ ). Surface c₁ c₂ The distance between is d₁ It becomes. Here, it should be noted that the surface of the diaphragm IR is treated as a surface different from the object-side surface of the glass plate H. However, as described above, the distance d in this example₁ Is 0.
[0074]
Next, the image side surface of the glass plate H is the third surface (c_Three ), The object side surface K3 of the lens LS3 is the fourth surface (c_Four ), The surface J3 on the image plane side is the fifth surface (c_Five ) Respectively. Further, the object side surface of the glass plate E is the sixth surface (c₆ ), The image side surface is the seventh surface (c₇ ) Respectively.
[0075]
Therefore, d₂ Is the thickness of the glass plate H, d_Three Is the surface on the image plane side of the glass plate H (c_Three ) And the first surface K3 of the lens LS3 (surface c on the object side)_Four ). Further, the first surface K3 of the lens LS3 (surface c on the object side)_Four ) And the second surface J3 (image surface side surface c) of the lens LS3._Five ) Is d_Four It becomes.
[0076]
Similarly, the second surface J3 (image surface side surface c) of the lens LS3._Five ) And the object-side surface of the glass plate E is d_Five The thickness of the glass plate E is d₆ It becomes. And the image side surface (c of the glass plate E)₇ ) And the image plane G is d₇ It becomes.
[0077]
【The invention's effect】
As described above, according to the present invention, a plastic diffractive molded lens that hardly causes a transfer failure of the diffractive groove shape even when a replica method represented by injection molding is applied, and the lens are used in an advantageous form. An optical system is provided. That is, by making a simple change to the shape of the diffraction groove forming portion, the irregularity of the groove shape that was particularly likely to occur in the diffraction groove on the convex surface was eliminated, and the annular diffraction grooves were regularly formed on the convex substrate. Plastic diffractive molded lenses can be provided at low cost. In addition, it is possible to provide a simple and excellent optical system in which a positive plastic diffractive molded lens having a diffraction groove on a convex surface is disposed as a single leaf.
[Brief description of the drawings]
FIG. 1 shows the flow of resin when manufacturing a conventional diffractive molded lens having a concentric annular diffraction groove on a convex surface by injection molding in the order of (a) → (b) → (c) → (d). It is shown in a sectional view later.
FIG. 2 is a view showing an example of a mold (main part member) used when manufacturing a plastic diffractive molded lens having the characteristics of the present invention, and (a) is a perspective view of (b). It is a top view of the shown metal mold | die (main part member).
FIG. 3 shows the flow of resin when a diffractive molded lens is manufactured by injection molding using the mold members 20 and 40 in the same manner as in FIG. 1, and (a) → (b) → (c) → ( d) are shown in cross-sectional view in order.
[Fig.4] Forming the ridges1 ofIt is a figure explaining an example.
[Fig.5] Forming the ridgesAnother example ofIt is a figure explaining about.
FIG. 6 shows the formation form of the ridges.referenceIt is a figure explaining an example.
FIG. 7 is a diagram illustrating an example of a diffractive molded lens having one convex portion.
FIG. 8 is a diagram illustrating an example of a diffractive molded lens having four ridges.
FIG. 9 is a diagram for explaining an example of an optical system in which an improved diffraction molded lens is arranged.
FIG. 10 is a diagram for explaining another example of an optical system in which an improved diffraction molded lens is arranged.
FIG. 11 is a diagram illustrating an example of an optical system in which another improved diffractive molding lens is disposed.
[Explanation of symbols]
  1 Mold
  2 cavity
  3 Diffraction groove transfer section
  4, 41 Loose concave surface
  10 Molten resin
  11 Leading part of molten resin flow
  12 Molten resin close to the diffraction groove transfer section
  13 Gap between diffraction groove transfer part and molten resin (unfilled part)
  20, 40, M, N, T Mold member
  21 Diffraction groove transfer section
  25, CV cavity
  31, 32, 33, GP Degassing groove
  E, H glass plate
  G Image plane
  IR aperture
  J1, J2, J3 Diffraction surface
  K1, K2 Loose convex surface
  K3 Loose concave surface
  L1, L2, LS1, LS2, LS3 Diffraction molded lens
  Q Concave surface with bottom R
  R Groove of diffraction groove transfer section
  W A linear part recessed at a certain depth from the concave surface Q (dashed line)
  Y A linear part formed so that the depth increases toward the outer edge.

Claims (5)

A plastic positive lens having at least one convex surface as a base surface,
Wherein the ring-shaped structure for diffraction is formed on the convex surface Rutotomoni, and narrow convex portion is provided so as to cross the ring-shaped structure,
The diffractive molded lens, wherein the convex portion is formed such that a top portion thereof is positioned on the base surface or parallel to the base surface and outside the base surface. The ring-shaped structure for diffraction and is formed for chromatic aberration correction, it has been diffraction molded lens according to claim 1. An optical system including a single plastic positive lens and a diaphragm, wherein the diaphragm is disposed closer to the object side than the positive lens;
  The positive lens has a convex surface as a base surface on the image surface side,
A diffraction ring zone structure is formed on the convex surface, and a thin ridge is provided so as to cross the ring zone structure,
The optical system, wherein the convex portion is formed such that a top portion thereof is positioned on the base surface or parallel to the base surface and outside the base surface. The optical system according to claim 3, wherein most of the refractive power of the entire diffractive molded lens is given to the convex surface. The optical system according to claim 3 or 4, wherein the diffraction ring zone structure is formed for correcting chromatic aberration .

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