JPH0525081B2 - - Google Patents
Info
- Publication number
- JPH0525081B2 JPH0525081B2 JP59251859A JP25185984A JPH0525081B2 JP H0525081 B2 JPH0525081 B2 JP H0525081B2 JP 59251859 A JP59251859 A JP 59251859A JP 25185984 A JP25185984 A JP 25185984A JP H0525081 B2 JPH0525081 B2 JP H0525081B2
- Authority
- JP
- Japan
- Prior art keywords
- lens
- mold
- fresnel lens
- fresnel
- lens portion
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Lifetime
Links
- 238000004519 manufacturing process Methods 0.000 claims description 14
- 239000000463 material Substances 0.000 claims description 14
- 238000000034 method Methods 0.000 claims description 8
- 238000000465 moulding Methods 0.000 claims description 4
- 238000003825 pressing Methods 0.000 claims description 4
- 230000009477 glass transition Effects 0.000 claims description 2
- 230000000630 rising effect Effects 0.000 claims description 2
- 230000000694 effects Effects 0.000 description 4
- 230000005540 biological transmission Effects 0.000 description 3
- 238000002834 transmittance Methods 0.000 description 2
- 230000003247 decreasing effect Effects 0.000 description 1
- 230000003287 optical effect Effects 0.000 description 1
- 239000002023 wood Substances 0.000 description 1
Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
- B29C43/00—Compression moulding, i.e. applying external pressure to flow the moulding material; Apparatus therefor
- B29C43/32—Component parts, details or accessories; Auxiliary operations
- B29C43/36—Moulds for making articles of definite length, i.e. discrete articles
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
- B29C43/00—Compression moulding, i.e. applying external pressure to flow the moulding material; Apparatus therefor
- B29C43/02—Compression moulding, i.e. applying external pressure to flow the moulding material; Apparatus therefor of articles of definite length, i.e. discrete articles
- B29C43/021—Compression moulding, i.e. applying external pressure to flow the moulding material; Apparatus therefor of articles of definite length, i.e. discrete articles characterised by the shape of the surface
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29L—INDEXING SCHEME ASSOCIATED WITH SUBCLASS B29C, RELATING TO PARTICULAR ARTICLES
- B29L2011/00—Optical elements, e.g. lenses, prisms
- B29L2011/0016—Lenses
- B29L2011/005—Fresnel lenses
Description
【発明の詳細な説明】
〔発明の利用分野〕
本発明は、投射型テレビ用の透過型スクリーン
に用いて好適なフレネルレンズとその製造方法に
関す。DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a Fresnel lens suitable for use in a transmission screen for a projection television and a method for manufacturing the same.
投射型テレビ等のスクリーンの透過率を上げる
ために、例えば特開昭57−61530号公報に示され
るように、フレネルレンズのレンズ面に反射防止
機構を有する微細な凹凸を形成する方法が提案さ
れている。
In order to increase the transmittance of screens such as projection televisions, a method has been proposed in which fine irregularities with an anti-reflection mechanism are formed on the lens surface of a Fresnel lens, as shown in, for example, Japanese Patent Laid-Open No. 57-61530. ing.
本方法によれば微細凹凸の集光作用により、レ
ンズ面での反射光が少くなりレンズの透過率が向
上し明るい画面が得られる。 According to this method, the light condensing effect of the fine asperities reduces the amount of light reflected on the lens surface, improves the transmittance of the lens, and provides a bright screen.
しかし、フレネルレンズに於いてはレンズ面を
形成しない非レンズ部があり、該非レンズ部から
の入光による散乱光が、スクリーンの鮮明度に影
響を与えていた。前記発明に於いては上記散乱光
については考慮されておらず、光学性能上若干の
問題点が残されていた。 However, the Fresnel lens has a non-lens portion that does not form a lens surface, and scattered light due to incident light from the non-lens portion affects the clarity of the screen. In the above-mentioned invention, the above-mentioned scattered light was not taken into consideration, and some problems remained in terms of optical performance.
本発明の目的は、フレネルレンズの非レンズ部
からの不要光線を防止した該フレネルレンズとそ
の製造方法を提供することにある。
An object of the present invention is to provide a Fresnel lens that prevents unnecessary light rays from entering the non-lens portion of the Fresnel lens, and a method for manufacturing the same.
上記目的を達成するために、非レンズ部に入光
する光線を、該部分で拡散させる機能を持たせる
ために、非レンズ部に凹凸溝を形成するものであ
る。
In order to achieve the above object, uneven grooves are formed in the non-lens portion in order to provide the non-lens portion with a function of diffusing light rays incident on the non-lens portion.
またかかるフレネルレンズの製造方法として
は、上型と下型に分離可能な製造用金型における
レンズ形状が不連続化した非レンズ部の立上がり
突起部を、上型と下型のプレス方向軸に対しオー
バハング状に構成するようにしたことを特徴とし
ている。 In addition, as a manufacturing method for such a Fresnel lens, in a production mold that can be separated into an upper mold and a lower mold, a rising protrusion of a non-lens part in which the lens shape is discontinuous is aligned with the pressing direction axis of the upper mold and lower mold. However, it is characterized by an overhanging structure.
以下、本発明の実施例を第１図〜第５図を用い
て説明する。
Embodiments of the present invention will be described below with reference to FIGS. 1 to 5.
第２図は投射型テレビの概要を示す断面図であ
る。１はケース、２は受像管、３はレンズ、４，
５はミラー、６はスクリーンである。以上の構成
に於いてレンズ３の中心より出た光L1は、ミラ
ー４，５を経てスクリーン６に到達する。一方レ
ンズ３の外周より出た光L2も同様にスクリーン
６に到達する。 FIG. 2 is a sectional view showing an outline of a projection television. 1 is a case, 2 is a picture tube, 3 is a lens, 4,
5 is a mirror, and 6 is a screen. In the above configuration, the light L1 emitted from the center of the lens 3 passes through the mirrors 4 and 5 and reaches the screen 6. On the other hand, light L 2 emitted from the outer periphery of the lens 3 also reaches the screen 6 in the same way.
このような種々の角度を持つ光Ｌで、スクリー
ン６上に画像を写し出すことになる。 An image is projected on the screen 6 using the light L having such various angles.
今、代表的な投射型テレビのスクリーン構成を
用いて、入射光の状態を更に詳細に説明する。 Now, the state of incident light will be explained in more detail using the screen configuration of a typical projection television.
第３図は一般に広く用いられている透過型スク
リーンの概要構成を示す斜視図である。７はレン
チキユラレンズ、８はフレネルレンズである。 FIG. 3 is a perspective view showing the general structure of a commonly used transmission screen. 7 is a lenticular lens, and 8 is a Fresnel lens.
第２図に示したスクリーン６への入射光Ｌはフ
レネルレンズ８により一定の方向を持つ光Loに
屈折し、レンチキユラレンズ７によりLa，Lbの
水平光線に拡散され水平指向性が与えられる。こ
れにより、見る人の水平方向位置がどの場所にあ
つても、一様の明るさと鮮明さを有する画像が得
られる。 The light L incident on the screen 6 shown in FIG. 2 is refracted by the Fresnel lens 8 into light Lo having a fixed direction, and is diffused into horizontal rays La and Lb by the lenticular lens 7, giving horizontal directivity. As a result, an image with uniform brightness and clarity can be obtained regardless of the horizontal position of the viewer.
第４図はフレネルレンズ８のみを取り上げて前
記入射光がどのように光線を描くかを表わしたも
のである。 FIG. 4 shows how the incident light draws rays by taking up only the Fresnel lens 8.
第４図はフレネルレンズ８の要部断面図であ
る。この形状は略同心円状に形成されている。フ
レネルレンズ８に入光する光Ｌは、レンズ形状と
なつているレンズ面８ａでは、所定の屈折角を持
つて略平行光線Loとなる。一方、非レンズ形状
となつている非レンズ部８ｂより入光した光はそ
のまま通過するか、若干の屈折角をもつてLcと
なつてフレネルレンズを通過する。該非レンズ部
からの屈折光Lcは、規則的に屈折した光線Loと
異なる光線となり、フレネルレンズの目的である
平行光線に集束させることができない。この場
合、投射型テレビのスクリーンでは、像がボケた
り画像全体が白つぽくなつたりして、鮮明な画像
が得られない。そこで該非レンズ部８ｂに、凹凸
溝を形成し、入射光を拡散させ、良好な画面を得
ようとするものである。 FIG. 4 is a sectional view of a main part of the Fresnel lens 8. This shape is substantially concentric. The light L entering the Fresnel lens 8 becomes a substantially parallel light beam Lo with a predetermined refraction angle on the lens surface 8a having a lens shape. On the other hand, light entering from the non-lens portion 8b having a non-lens shape passes through the Fresnel lens as it is, or changes to Lc with a slight refraction angle and passes through the Fresnel lens. The refracted light Lc from the non-lens portion becomes a light beam different from the regularly refracted light beam Lo, and cannot be focused into parallel light beams, which is the purpose of the Fresnel lens. In this case, on the projection television screen, the image becomes blurred or the entire image becomes white, making it impossible to obtain a clear image. Therefore, uneven grooves are formed in the non-lens portion 8b to diffuse the incident light and obtain a good screen.
第１図を用いて凹凸溝の形成方法すなわち本発
明によるフレネルレンズの製造方法について説明
する。第１図はフレネルレンズを得るための、本
発明の製造方法を示す要部断面図である。９は金
型（下型）、１０はレンズ材料である。第４図の
製品に対応し、金型の表面はレンズ形状部９ａと
非レンズ形状部９ｂとで構成される。非レンズ形
状部９ｂは金型のプレス方向（矢印で示す）と角
度θで交わつており、その先端９ｃはオーバハン
グしている。この形状は略同心円状に形成されて
いる。 A method for forming uneven grooves, that is, a method for manufacturing a Fresnel lens according to the present invention will be described with reference to FIG. FIG. 1 is a sectional view of essential parts showing the manufacturing method of the present invention for obtaining a Fresnel lens. 9 is a mold (lower mold), and 10 is a lens material. Corresponding to the product shown in FIG. 4, the surface of the mold is composed of a lens-shaped portion 9a and a non-lens-shaped portion 9b. The non-lens shaped portion 9b intersects the pressing direction of the mold (indicated by an arrow) at an angle θ, and its tip 9c overhangs. This shape is substantially concentric.
以上の構成からなる金型を用いて、軟化温度領
域に加熱したレンズ材料１０を形成する。該軟化
温度領域は材料が塑性領域と流動領域の介在する
温度であり、例えばその材料のガラス転移温度付
近が好適である。次に適宜加熱れた金型９と上型
（図示せず）との間にレンズ材料１０を介在した
状態で、前記金型を矢印の方向に加圧付加すれ
ば、レンズ材料は金型９の先端部９ｃに塑性変形
と流動変形の両方を受けながら変形し、最終的に
金型のレンズ形状９ａに密着し、レンズ形状部９
ａに接した部分のみ、レンズ材料の温度と金型温
度により滑らかなレンズ面が形成される。 Lens material 10 heated to a softening temperature range is formed using a mold having the above configuration. The softening temperature region is a temperature at which the material has a plastic region and a flow region, and is preferably around the glass transition temperature of the material, for example. Next, with the lens material 10 interposed between the suitably heated mold 9 and the upper mold (not shown), pressurization is applied to the mold in the direction of the arrow, so that the lens material is transferred to the mold 9. The tip 9c of the lens deforms while undergoing both plastic deformation and flow deformation, and finally comes into close contact with the lens shape 9a of the mold, forming the lens shape part 9.
A smooth lens surface is formed only at the portion in contact with a due to the temperature of the lens material and the temperature of the mold.
一方、先端部９ｃにより塑性変形成形される非
レンズ部は、金型のオーバハング効果により、金
型先端部９ｃの形状によつて一意的にフレネルレ
ンズ８の非レンズ部８ｂの形状が決まるため、レ
ンズ材料と金型は該非レンズ部９ｂでは密着せ
ず、空気層が介在する形となる。 On the other hand, the shape of the non-lens part 8b of the Fresnel lens 8 that is plastically deformed by the tip 9c is uniquely determined by the shape of the die tip 9c due to the overhang effect of the die. The lens material and the mold do not come into close contact with each other in the non-lens portion 9b, with an air layer intervening therebetween.
金型の先端９ｃに凸凹を持たせることにより、
成形されたフレネルレンズ８の非レンズ部８ｂの
形状は、金型先端９ｃの凸凹形状に対応した凹凸
形状が第１図の矢印方向に連続して形成されるた
め、凹凸の溝が形成されることになる。 By making the tip 9c of the mold uneven,
The shape of the non-lens portion 8b of the molded Fresnel lens 8 is such that a concavo-convex shape corresponding to the concave-convex shape of the mold tip 9c is formed continuously in the direction of the arrow in FIG. 1, so that an uneven groove is formed. It turns out.
本発明の他の製造方法について説明する。金型
の非レンズ形状部９ｂに凸凹溝を形成し、前記実
施例と同様にレンズ材料１０を加熱して金型９に
よつて第１図の矢印方向に加圧する。この際、前
記金型の凸凹溝の形状をフレネルレンズの非レン
ズ部に密着転写させる。すなわち、金型の凸凹溝
がレンズ材料に密着転写されて、フレネルレンズ
の非レンズ部には凹凸溝が形成される。この製造
方法に於いては、加圧中にレンズ面と同様に非レ
ンズ部も金型と密着転写させることによりフレネ
ルレンズの非レンズ部に凹凸溝を形成することが
できるため、金型には第１図に示したオーバハン
グは特に必要としない。成形温度領域は、材料の
塑性領域だけでなく流動領域でも良い。 Another manufacturing method of the present invention will be explained. Convex and concave grooves are formed in the non-lens shaped portion 9b of the mold, and the lens material 10 is heated and pressed by the mold 9 in the direction of the arrow in FIG. 1 in the same manner as in the previous embodiment. At this time, the shape of the grooves of the mold is closely transferred to the non-lens portion of the Fresnel lens. That is, the uneven grooves of the mold are closely transferred to the lens material, and the uneven grooves are formed in the non-lens portion of the Fresnel lens. In this manufacturing method, uneven grooves can be formed on the non-lens part of the Fresnel lens by closely transferring the non-lens part to the mold as well as the lens surface during pressurization, so the mold is The overhang shown in FIG. 1 is not particularly required. The forming temperature range may be not only the plastic range of the material but also the flow range.
以上本発明の製造方法について説明したが、前
者の実施例では、加圧成形後の離型が問題となる
傾向にある。金型先端部のオーバハングのため
に、アンダーカツトになり易い。第５図は木製造
金型の断面図であるが、本金型９はいくつかのブ
ロツクから構成されており、離型に際してはまず
Ａブロツクを矢印の如く後退させ、順次Ｂブロツ
ク、Ｃブロツク、Ｄブロツクと後退させ、製品よ
り離型する。各ブロツクの後退方向は、オーバハ
ング角θと同一方向であるため、製品に何等離型
力を加えることなく離型できる。以上説明したよ
うに、本発明は簡単にして極めて容易に凹凸溝を
形成することができ、その効果は顕著である。 The manufacturing method of the present invention has been described above, but in the former embodiment, mold release after pressure molding tends to be a problem. Due to overhang at the tip of the mold, undercuts are likely to occur. FIG. 5 is a sectional view of a wood manufacturing mold. This mold 9 is composed of several blocks. When releasing the mold, first move the A block backward as shown by the arrow, then move on to the B block and C block in turn. , the D block is moved back, and the mold is released from the product. Since the receding direction of each block is the same as the overhang angle θ, the product can be released from the mold without applying any release force. As explained above, according to the present invention, uneven grooves can be formed very easily, and the effect thereof is remarkable.
本発明によれば、金型に施した凸凹形状に対応
した凹凸溝を、フレネルレンズの非レンズ部にレ
ンズ面成形と同時に容易に形成できるため、非レ
ンズ部に入光する光は拡散され、投射型テレビ用
スクリーンに適用した場合には、ボケや画面の白
つぽさ（コントラストの低下）が低減された鮮明
な画像が得られる。
According to the present invention, uneven grooves corresponding to the uneven shapes formed on the mold can be easily formed on the non-lens portion of the Fresnel lens at the same time as lens surface molding, so that light entering the non-lens portion is diffused. When applied to a projection television screen, a clear image with reduced blur and screen whiteness (decreased contrast) can be obtained.
第１図は本発明による製造方法を示す要部断面
図、第２図は投射型テレビの概要断面図、第３図
は透過型スクリーンの概要斜視図、第４図はフレ
ネルレンズの光線屈折を示す要部断面図、第５図
は本発明の製造に用いる金型の断面図、である。
１……ケース、２……受像管、３……レンズ、
４，５……ミラー、６……スクリーン、７……レ
ンチキユラレンズ、８……フレネルレンズ、９…
…金型、１０……レンズ材料。
Fig. 1 is a cross-sectional view of a main part showing the manufacturing method according to the present invention, Fig. 2 is a schematic cross-sectional view of a projection type television, Fig. 3 is a schematic perspective view of a transmission screen, and Fig. 4 shows the light refraction of a Fresnel lens. FIG. 5 is a sectional view of a main part shown, and FIG. 5 is a sectional view of a mold used for manufacturing the present invention. 1... Case, 2... Picture tube, 3... Lens,
4, 5... Mirror, 6... Screen, 7... Lenticular lens, 8... Fresnel lens, 9...
...Mold, 10...Lens material.
Claims (1)
レビ等の表示部であるスクリーンを構成するフレ
ネルレンズにおいて、該フレネルレンズは、非レ
ンズ部に凹凸溝を設けたことを特徴とするフレネ
ルレンズ。 ２ 上型と下型に分離可能な金型であつて、該金
型におけるレンズ形状が不連続化した非レンズ部
の立上がり突起部を上型と下型のプレス方向軸に
対しオーバハング状に形成し、かつ前記突起部に
凸凹を構成した成形金型を用い、予め材料のガラ
ス転移温度領域に加熱したシート状材料を前記し
た上型と下型の間に介在させ、加熱した前記金型
に圧力を加えプレスして、非レンズ部に凹凸溝を
形成することを特徴とするフレネルレンズの製造
方法。 ３ 予め凸凹溝を設けた非レンズ部を有するフレ
ネルレンズ成形金型を用いて、フレネルレンズの
非レンズ部に、凹凸溝を形成することを特徴とす
るフレネルレンズの製造方法。 ４ 非レンズ部に凹凸溝を設けたフレネルレンズ
とレンチキユラレンズとを組み合わせて構成した
スクリーンを備えたことを特徴とする投射型テレ
ビ。[Scope of Claims] 1. A Fresnel lens that is used in combination with a lenticular lens to constitute a screen that is a display section of a projection television, etc., wherein the Fresnel lens is characterized in that a concave-convex groove is provided in a non-lens portion. lens. 2 A mold that can be separated into an upper mold and a lower mold, in which a rising protrusion of a non-lens portion in which the lens shape is discontinuous is formed in an overhanging shape with respect to the press direction axes of the upper mold and lower mold. Then, using a molding die in which the protrusions are formed with unevenness, a sheet material heated in advance to the glass transition temperature range of the material is interposed between the upper mold and the lower mold, and the heated mold is heated. A method for manufacturing a Fresnel lens, which comprises applying pressure and pressing to form uneven grooves in the non-lens portion. 3. A method for manufacturing a Fresnel lens, which comprises forming uneven grooves in a non-lens portion of a Fresnel lens using a Fresnel lens molding die having a non-lens portion provided with grooves in advance. 4. A projection television characterized by comprising a screen constructed by combining a Fresnel lens and a lenticular lens with grooves provided in the non-lens portion.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP59251859A JPS61130903A (en) | 1984-11-30 | 1984-11-30 | Fresnel lens and its production |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP59251859A JPS61130903A (en) | 1984-11-30 | 1984-11-30 | Fresnel lens and its production |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JPS61130903A JPS61130903A (en) | 1986-06-18 |
| JPH0525081B2 true JPH0525081B2 (en) | 1993-04-09 |
Family
ID=17228980
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP59251859A Granted JPS61130903A (en) | 1984-11-30 | 1984-11-30 | Fresnel lens and its production |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JPS61130903A (en) |
Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPH0267326U (en) * | 1988-11-10 | 1990-05-22 | ||
| JP2901727B2 (en) * | 1990-09-19 | 1999-06-07 | 株式会社日立製作所 | Fresnel lens |
Citations (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS50125755A (en) * | 1974-03-19 | 1975-10-03 | ||
| JPS5117452A (en) * | 1974-08-02 | 1976-02-12 | Ichiro Hosaka | FURENERURENZU |
| JPS52143847A (en) * | 1976-05-26 | 1977-11-30 | Mitsubishi Electric Corp | Optical lens |
| JPS52145238A (en) * | 1976-05-28 | 1977-12-03 | Ichirou Hosaka | Method of making mold for fresnel lens |
| JPS56140335A (en) * | 1980-04-04 | 1981-11-02 | Matsushita Electric Ind Co Ltd | Transmission type projecting screen |
| JPS56142501A (en) * | 1980-04-08 | 1981-11-06 | Matsushita Electric Ind Co Ltd | Fresnel lens sheet |
| JPS56144927A (en) * | 1980-04-14 | 1981-11-11 | Matsushita Electric Ind Co Ltd | Manufacture of fresnel lens |
| US4456344A (en) * | 1981-07-23 | 1984-06-26 | A.T.B. S.P.A. | Fresnel lens, and a method and mold for manufacturing it |
Family Cites Families (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS5229148U (en) * | 1975-08-22 | 1977-03-01 | ||
| JPS5389341U (en) * | 1976-12-22 | 1978-07-21 |
-
1984
- 1984-11-30 JP JP59251859A patent/JPS61130903A/en active Granted
Patent Citations (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS50125755A (en) * | 1974-03-19 | 1975-10-03 | ||
| JPS5117452A (en) * | 1974-08-02 | 1976-02-12 | Ichiro Hosaka | FURENERURENZU |
| JPS52143847A (en) * | 1976-05-26 | 1977-11-30 | Mitsubishi Electric Corp | Optical lens |
| JPS52145238A (en) * | 1976-05-28 | 1977-12-03 | Ichirou Hosaka | Method of making mold for fresnel lens |
| JPS56140335A (en) * | 1980-04-04 | 1981-11-02 | Matsushita Electric Ind Co Ltd | Transmission type projecting screen |
| JPS56142501A (en) * | 1980-04-08 | 1981-11-06 | Matsushita Electric Ind Co Ltd | Fresnel lens sheet |
| JPS56144927A (en) * | 1980-04-14 | 1981-11-11 | Matsushita Electric Ind Co Ltd | Manufacture of fresnel lens |
| US4456344A (en) * | 1981-07-23 | 1984-06-26 | A.T.B. S.P.A. | Fresnel lens, and a method and mold for manufacturing it |
Also Published As
| Publication number | Publication date |
|---|---|
| JPS61130903A (en) | 1986-06-18 |
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