Lens array, method of making the same, and lens

A lens array includes a plurality of lenses, a holder portion for fixing the lenses, and an acrylic transparent layer for covering the lens surfaces of the respective lenses. The holder portion and the lenses are made of the same transparent resin to be formed as a one-piece element. The lens array also includes a dark-colored light shielding layer for preventing the unwanted passage of light. The transparent layer is formed on the light shielding layer for preventing the latter from peeling off.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a lens array. In particular, it relates to a lens array of the type which is used in an optical device such as a contact-type image sensor for focusing the images on a document onto linearly arranged light receiving elements. The present invention also relates to a method of making such a lens array and a lens.

2. Description of the Related Art

A conventional lens array of the above-mentioned type is provided with a plurality of lenses which are produced separately from each other. These lenses are arranged in an array and held together by a holder which is prepared separately from the lenses. The lenses may be convex lenses made of glass, while the holder may be made of a synthetic resin. In place of the convex lenses, a plurality of self-focusing lenses (rod lenses) may be used for producing the image of an object in a non-inverting and non-magnifying manner.

The conventional lens array is disadvantageous in the following points.

Specifically, the production procedure of the conventional lens array tends to be unduly complicated since the respective lenses and the holder are produced separately from each other. The smallness of each lens (the diameter may often be smaller than 1 mm) and the multiplicity of the lenses aggravate the situation. As readily understood, it is very difficult to accurately position a great number of small lenses within the holder.

Another drawback of the conventional lens array is that light tends to be unduly scattered at the lens surface of each lens due to unevenness of the lens surface. With the use of such a lens array, reproduction of a clear image cannot be expected.

SUMMARY OF THE INVENTION

The present invention has been proposed under the abovedescribed circumstances, and its object is to produce, efficiently and at low costs, lens arrays or lenses exhibiting an excellent optical performance.

According to a first aspect of the present invention, there is provided a lens array comprising: a plurality of lenses each of which is provided with a lens surface; a holder portion for fixing the lenses; and a transparent layer for covering at least the lens surface of each lens.

With such an arrangement, the lens surface of each lens is smoothed out by the transparent layer, which is advantageous to improving the optical performance of the lens. The transparent layer may be made of an acrylic material.

Preferably, the holder portion and the lenses may be made of a same transparent resin material and formed as a one-piece element. A lens array having such features is readily produced by a molding technique. Thus, in comparison with the conventional lens array, the production efficiency is improved and the production costs are advantageously reduced.

Preferably, a light shielding layer may further be formed on at least part of the holder portion. The light shielding layer serves to prevent unwanted light from entering or leaving the lens array.

Preferably, the holder portion may be provided with a plurality of grooves, wherein each of the lenses is located between two grooves. Further, each of the grooves may be provided with inner wall surfaces covered by the light shielding layer. With such an arrangement, the cross talk of light is prevented, which improves the optical performance of the lens array.

Preferably, the light shielding layer may be rendered dark-colored (in particular, black) for facilitating the absorption of unwanted light.

Preferably, the transparent layer may overlap the light shielding layer. In this manner, the light shielding layer is protected by the transparent layer from mechanical damage, while also being secured to the holder portion or the lenses under the transparent layer.

Preferably, the lens array of the present invention may further comprise engaging means for associating with an additional lens array. With such an arrangement, a lens array assembly is readily constituted by combining more than one lens array.

Preferably, each of the lenses may be provided with first and second lens surfaces which are unequal in diameter to each other.

According to a second aspect of the present invention, there is provided a method of making a lens array. The method comprises the steps of: molding a transparent resin material into a resin element provided with a plurality of lenses; and forming a transparent layer for covering at least a lens surface of each lens.

Preferably, the method may further comprise a step of dividing the resin element into a plurality of lens arrays.

Preferably, the transparent layer may be formed by spraying a transparent acrylic material onto the lens surface of each lens. In this manner, the acrylic material can be uniformly applied over a wide area. In general, an acrylic paint material has advantageously high transparency. Also, an acrylic paint is easy to handle and less expensive than other materials, which is advantageous to reducing the production costs.

Preferably, the viscosity of the acrylic material may be in a range of 10 mP-100 mP at 20 C.

Preferably, the method of the present invention may further comprise a step of forming a light shielding layer on the resin element before the forming of the transparent layer.

Preferably, the transparent layer may overlap the light shielding layer. With such an arrangement, the transparent layer, which is arranged on the light shielding layer, prevents the light shielding layer from peeling off.

Preferably, the light shielding layer may be formed by ejecting dark-colored ink onto the resin element. The ejecting of the ink may be performed by an inkjet printer.

According to a third aspect of the present invention, there is provided a lens comprising: a transparent body provided with a lens surface; and a transparent layer covering the lens surface.

The lens surface may be curved. For instance, the lens surface may be convex or concave.

Other features and advantages of the present invention will become apparent from the detailed description given below with reference to the accompanying drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference is first made to FIGS. 1-12 illustrating a method of collectively making a plurality of lens arrays embodying the present invention.

In accordance with the illustrated method, first an interim resin product 1 shown in FIGS. 1-3 is prepared. The interim product 1 is a plate or sheet having a generally rectangular configuration and may be made of a transparent synthetic resin material such as PMMA (polymethylmethacrylate) or PC (polycarbonate), which exhibit excellent transparency and sufficient mechanical strength.

As shown in FIGS. 1-3 , the interim product 1 is provided with a plurality of lenses 11 , a holder portion 10 for holding the lenses 11 , a plurality of grooves 14 , a plurality of projections 12 and a plurality of recesses 13 . In the illustrated example, the lenses 11 are grouped into ten arrays ( 1 A- 1 K) each of which extends longitudinally of the rectangular interim product 1 , as shown in FIG. 1 A. In each lens array, the individual lenses 11 are arranged at a constant pitch P (1 mm for example). The grooves 14 are formed in both the upper surface and the lower surface of the interim product 1 , as seen from FIG. 1B or FIG. 3 . In plan view ( FIG. 1 ) or bottom view (not shown), each lens 11 is flanked by two grooves 14 . The ten lens arrays 1 A- 1 K are spaced from each other in the widthwise direction of the interim product 1 . As shown in FIG. 1B , each lens array has a prescribed effective length EL. For instance, the effective length EL may be rendered greater than 210 mm for dealing with a DIN A4-size document.

As best shown in FIG. 3 , each of the lenses 11 is provided with a convex upper lens surface 11 a and a convex lower lens surface 11 b opposite to the upper lens surface 11 a . These lens surfaces may be spherical or non-spherical. A spherical lens surface is made more easily than a non-spherical surface. However, a non-spherical lens surface is preferable for reducing aberration and hence for producing a distinct image of an object. The diameters of the upper and the lower lens surfaces are equal and may be about 0.6 mm.

The holder portion 10 is the remainder of the interim product 1 except for the lenses 11 and the projections 12 .

As mentioned above, the grooves 14 are formed on the upper and the lower side of the interim product 1 . As shown in FIGS. 1A and 2 , each groove 14 has a rectangular opening which is elongated transversely to the longitudinal direction of the lens array. As shown in FIG. 3 , each groove 14 is provided with inclined inner walls 14 a , 14 b and tapers toward the bottom wall 14 c of the groove.

As will be described later, the projections 12 and the recesses 13 are provided for causing a lens array obtained from the interim product 1 to be attached to another lens array obtained from the same interim product 1 . As shown in FIGS. 1A and 1B , the projections 12 are formed on the upper surface of the interim product 1 . One of the projections 12 is located at the right end of the second lens array 1 B, while the counterpart projection is located at the left end of the same lens array 1 B. Similarly, the remaining projections 12 are located at the right end or left end of the fourth ( 1 E) or sixth ( 1 F) or eighth ( 1 H) or tenth ( 1 K) lens array.

On the other hand, the recesses 13 are formed in the lower surface of the interim product 1 . As shown in FIG. 1A , one recess 13 is located at the right or left end of any one of the first ( 1 A), third ( 1 C), fifth ( 1 E), seventh ( 1 G) and ninth ( 1 J) lens arrays.

As shown in FIG. 1A , the interim product 1 is provided with two shorter end portions 1 a , 1 b , at which the projections 12 and the recesses 13 are arranged. The interim product 1 is also provided with two longer end portions 1 c , id extending perpendicularly to the shorter end portions 1 a , 1 b .

Further, the interim product 1 is provided with a plurality of elongated intermediate portions 1 e extending in parallel to the longer end portions 1 c , 1 d . The intermediate portions 1 e separate the respective lens arrays 1 A- 1 K from each other. The above-mentioned end portions 1 a , 1 b , 1 c , 1 d and the intermediate portions 1 e are greater in thickness than the other portions of the interim product 1 , as can be seen from FIGS. 2 and 3 .

The interim product 1 may be produced by a molding technique using an upper molding member 6 A and a lower molding member 6 B shown in FIGS. 4 and 5 . The paired molding members 6 A and 6 B are formed with inner surfaces defining a cavity 65 . These inner surfaces include a plurality of concave portions 11 a and 11 b which correspond to the upper lens surfaces 11 a and the lower lens surfaces 11 b , respectively. As best shown in FIG. 5 , the molding members 6 A and 6 B are formed with a plurality of protrusions 14 corresponding to the grooves 14 of the interim product 1 . The upper molding member 6 A is also provided with a plurality of recesses 12 for forming the projections 12 of the interim product 1 . The lower molding member 6 B is provided with a plurality of protrusions 13 for forming the recesses 13 on the bottom side of the interim product 1 .

The molding procedure may be performed in the following manner. First, a molten synthetic resin material is poured into the cavity 65 formed by the cooperation of the two molding members 6 A and 6 B (FIG. 4 ). Then, after filling the cavity 65 , the poured resin material is hardened. Then, as shown in FIG. 5 , the upper and the lower molding members 6 A, 6 B are separated from each other, whereby a desired interim product 1 is obtained.

In the illustrated example, the four end portions 1 a - 1 d and the intermediate portions 1 e have a comparatively great thickness, as mentioned above. Accordingly, the cavity 65 is rendered greater in thickness at portions corresponding to the above-mentioned thicker portions of the interim product 1 . Such an arrangement is advantageous to causing the poured molten resin material to smoothly fill up the cavity 65 .

According to the present invention, the grooves 14 of the interim product 1 may not be made by a molding method as described above. Instead, an interim resin product with no such grooves may be subjected to mechanical processing using a cutting tool such as an end mill. The grooves 14 may also be made by laser processing.

Following the molding procedure shown in FIGS. 4 and 5 , a step of applying black paint is performed to form a light shielding layer 15 on the interim product 1 , as shown in FIG. 6 . The light shielding layer 15 covers most of the surfaces of the interim product 1 but is not formed on the upper and lower lens surfacese 11 a , 11 b of the respective lenses 11 .

As shown in FIG. 7 , use may be made of an inkjet printer 8 for applying the black paint onto the prescribed portions of the interim product 1 . The inkjet printer 8 includes a printer head 81 provided with an inkjet nozzle 81 a . The printer head 81 is slidably supported by a horizontal guide rod 80 . A non-illustrated driving mechanism causes the printer head 81 to slide along the guide rod 80 , as indicated by the two-headed arrow in FIG. 7 . The guide rod 80 is not stationary relative to the interim product 1 but horizontally movable in a direction perpendicular to the reciprocative directions of the inkjet printer 8 . Thus, the printer head 81 is cause to move in a horizontal plane relative to the interim product 1 . Though not illustrated in FIG. 7 , a controller is provided for causing the printer head 8 to eject ink onto a desired part of the external surface of the interim product 1 .

With the use of the inkjet printer 8 operating under the control of the non-illustrated controller, the applying of ink can be performed only to the selected portions of the interim product 1 . Thus, without using a mask, the light shielding layer 15 is properly formed on the interim product 1 in a manner avoiding the lens surfaces 11 a , 11 b of the respective lenses 11 .

As shown in FIGS. 6 and 7 , each groove 14 tapers toward the bottom surface thereof, so that ink ejected from the inkjet nozzle 81 a is properly applied onto the inclined inner surfaces as well as the bottom surface of the groove 14 . When the grooves 14 taper to a smaller degree than in the illustrated example (for instance, when the inclined inner surfaces of the groove 14 are substantially upright), the ejected ink may fail to be properly applied onto the inner surfaces of the groove 14 . In this case, a relatively large amount of ink may be ejected into each groove 14 so that the groove is generally filled with the ink.

According to the present invention, the light shielding layer 15 may not necessarily be made by the inkjet printer 8 . Instead, the interim product 1 may be immersed in black paint for a while and taken out. Then, the paint adhered to the upper and lower lens surfaces 11 a , 11 b of the respective lenses 11 may be wiped away before the paint becomes hard. Of course, a masking technique may be used for painting the interim product 1 except for the lens surfaces 11 a , 11 b of the respective lenses 11 . Advantageously, the light shielding layer 15 is black. However, other dark colors may suffice if the layer 15 can properly shield light.

Referring to FIG. 8 , a transparent layer 16 is formed on all or part of the surfaces of the interim product 1 after the light shielding layer 15 is formed. As illustrated, the transparent layer 16 covers, at least, the upper and lower lens surfaces 11 a , 11 b of each lens 11 and the light shielding layer 15 . The transparent layer 16 may be made of an acrylic resin material and has a small thickness of 5-10 m. At the upper and lower lens surfaces 11 a , 11 b in particular, the transparent layer 16 is rendered to have a uniform (or generally uniform) thickness, so that the curvature of the transparent layer 16 is substantially equal to that of the lens surfaces 11 a , 11 b.

The forming of the transparent layer 16 may be performed using a paint-spraying device 85 , as shown in FIG. 9 . The spraying device 85 is provided with a spray head 85 a and arranged to slide on a horizontal guide rod 85 b extending longitudinally of the interim product 1 . As the spraying device 85 is being moved along the guide rod 85 b , a suitable amount of transparent paint is being sprayed from the nozzle of the spray head 85 a to be applied onto the interim product 1 . For moving the spraying device 85 in the widthwise direction of the interim product 1 , the guide rod 85 b is arranged to move in that direction relative to the interim product 1 , which is stationary. Alternatively, the interim product 1 may be moved relative to the guide rod 85 b which is stationary.

One of the advantages in forming the transparent layer 16 is to smooth out the lens surfaces 11 a , 11 b of each lens 11 which may originally be rather rough, as shown in FIG. 10 . With the transparent layer 16 , light incident upon or leaving the lens 11 is prevented from being unduly scattered at the upper or lower lens surface 11 a or 11 b.

A preferable acrylic resin material for forming the transparent layer 16 may be water-base acrylic transparent varnish (produced by Sunday Paint) diluted 1.5-10 times with distilled water. (A varnish diluted n times with water may contain 1 cc of varnish and (n 1)cc of water.) The inventors of the present invention have found that almost no bubbles are generated in the transparent layer 16 when the above-mentioned diluted varnish is sprayed onto the interim product 1 at room temperature. Another preferable paint material for forming the transparent layer 16 may be the above-mentioned water-base acrylic transparent varnish diluted 1.5-10 times with ethyl alcohol. With this paint material again, no bubbles are generated in the resulting layer 16 . Having conducted some experiments, the inventors also have found that the resulting transparent layer 16 will exhibit excellent surface smoothness when the viscosity of the acrylic resin material to be used is in a range of 10-100 mP (20 C.).

Another advantage to forming the transparent layer 16 is as follows. Referring to FIG. 10 , the resulting transparent layer 16 overlaps the light shielding layer 15 . In this manner, the transparent layer 16 prevents the light shielding layer 15 from peeling off the interim product 1 . It should be noted here that the interim product 1 , which is made of PMMA, can be more firmly attached to the transparent layer 16 (made of acrylic material) than to the light shielding layer 15 . Thus, the transparent layer 16 , comparatively firmly attached to the exposed lens surfaces 11 a or 11 b , keeps the light shielding layer 15 attached to the interim product 1 .

Referring to FIG. 11 , the interim product 1 is divided along the respective Nb Nb lines by a cutting device after the transparent layer 16 is formed. Thus, a predetermined number of lens arrays 1 are obtained. All of the obtained lens arrays 1 are identical to each other, though half of them are formed with recesses 13 at their ends, while the other half are formed with projections 12 instead of the recesses 13 . For instance, the first lens array 1 ( 1 A) is provided at its bottom surface with recesses 13 , while the second lens array 1 ( 1 B) is provided at its top surface with projections 12 . As readily seen, the longitudinal side surfaces 1 f , 1 g of each lens array 1 are not covered by the light shielding layer 15 . Where appropriate, those side surfaces may also be coated with black paint.

The collective production of a plurality of lens arrays from a single mother board is advantageous to improving the production efficiency. In particular, the forming of the light shielding layer 15 and transparent layer 16 is performed collectively for all of the lens arrays 1 before dividing the interim product 1 . In this manner, the time needed to produce the lens arrays 1 is greatly reduced.

According to the present invention, the dividing of the interim product 1 into smaller elements may be performed as follows. First, the interim product 1 is formed with separation-aiding grooves each of which extends in a corresponding one of the intermediate portions 1 e . Then, an external force is applied on the interim product 1 to simply snap it along the Nb Nb lines.

The lens arrays 1 obtained from the interim product 1 may be used in the following manners.

Referring to FIGS. 12 and 13 , a lens array assembly A 1 is provided by the combination of two lens arrays. Specifically, the first lens array 1 A is mounted on the second lens array 1 B with the projections 12 of the second lens array 1 B fitted into the recesses of the first lens array 1 A. As will be described later, the lens array assembly A 1 is designed to focus an image of a selected object in a non-magnifying and non-inverting manner.

The first and the second lens arrays 1 A and 1 B are identical to each other except for the recesses 13 or projections 12 . Thus, in the assembled state, the optical axes C of the respective lenses 11 of the first lens array 1 A coincide with the optical axes of the respective lenses 11 of the second lens array 1 B. More precisely, the optical axis C of the lens 11 A 1 of the first lens array 1 A coincides with the optical axis of the counterpart lens 11 B 1 of the second lens array 1 B. Similarly, the optical axis C of the lens 11 A 2 of the first lens array 1 A coincides with the optical axis of the counterpart lens 11 B 2 of the second lens array 1 B, and so on.

According to the present invention, in each of the first and second lens arrays 1 A and 1 B, the lenses 11 and the holder portion 10 are formed integral with each other. In other words, the lenses 11 and the holder portion 10 are formed as a one-piece element.

FIG. 14A illustrates the function of the lens array assembly A 1 . For simplicity of illustration, the transparent layers 16 formed on the first and second lens arrays are not depicted in the figure. As shown, light reflected on an object (c b a), which is elongated along the starting line S, will pass through the lenses 11 of the first lens array 1 A and then the lenses 11 of the second lens array 1 B to finally reach the focusing position F. In the illustrated example, any one of the lenses 11 of the first lens array 1 A and its counterpart lens 11 of the second lens array 1 B cooperate to behave like a self-focusing lens. Thus, the non-inverted and non-magnified image (c b a ) of the object (c b a) at the point S is generated at the focusing position F.

The lens array assembly Al described above may preferably be used in a contact-type scanner, a line image sensor, etc. As stated above, the lens surfaces 11 a , 11 b of the respective lenses 11 are smoothed out by the transparent layer 16 . Thus, the resulting image (c b a ) at the focusing position F is highly distinctive. Further, the lens array assembly A 1 can be made advantageously compact since it only consists of two elongated lens arrays each of which has a small width.

According to the illustrated arrangement, the light shielding layers 15 prevent the light reflected on the object (c b a) from entering the lens assembly Al through any portion other than the lens surfaces 11 a of the first lens array 1 A. The light shielding layers 15 also prevent the cross talk of light. Without these layers, as shown in FIG. 14B , a light beam Lb 1 may unduly stray into a wrong lens 11 Ay from the upper lens 11 Ax within the first lens array 1 A, or a light beam Lb 2 passing through the lens 11 Ay of the first lens array 1 A may go into a wrong lens 11 Bz of the second lens array 1 B other than the intended lens 11 By.

Due to the above preventive features, the lens assembly A 1 of the present invention can provide a clear, non-inverted and non-magnified image of an object.

FIG. 15 illustrates another type of lens assembly provided in accordance with the present invention. The illustrated lens assembly A 2 consists of two different lens arrays 1 C and 1 D. Each of the lens arrays 1 C, 1 D is provided with a plurality of convex lenses 11 with aligned optical axes C, as in the first and second lens arrays 1 A, 1 B.

Differing from the first and second lens arrays 1 A, 1 B, the upper or third lens array 1 C is formed with grooves 14 only on one side (the upper side in FIG. 15 ). The depth s 1 of each groove 14 of the third lens array 1 C is greater than the counterpart of the first or second lens array 1 A, 1 B. On the lower side of the lens array 1 C, flat portions 19 are formed between the second lens surfaces 11 b of the respective lenses 11 . As seen from FIG. 15 , the first lens surface 11 a of each lens 11 of the third lens array 1 C is smaller in diameter than the second lens surface 11 b . A dark-colored (preferably, black) light shielding layer 15 is formed on the upper and lower sides of the lens array 1 C except at least the first and second lens surfaces 11 a , 11 b of the respective lenses 11 . The light shielding layer 15 and these lens surfaces are covered by a transparent layer 16 .

As opposed to the third lens array 1 C, the lower or fourth lens array 1 D is not provided with grooves between the lenses 11 nor with a light shielding layer. The first lens surfaces 11 e of the fourth lens array 1 D are, in diameter, equal to or greater than the second lens surfaces 11 b of the third lens array 1 C. The second lens surfaces 11 f of the fourth lens array 1 D are greater in diameter than the first lens surfaces 11 e . As viewed longitudinally of the fourth lens array 1 D, the second lens surfaces 11 f are continuous, whereas the first lens surfaces 11 e are spaced from each other. A transparent layer 16 for smoothing out surface irregularities is formed to cover at least the first lens surfaces 11 e and the second lens surfaces 11 f . In the assembled state, the second lens surfaces 11 b of the third lens array 1 C are arranged very close to the first lens surfaces lie of the fourth lens array 1 D.

As shown in FIG. 16 , the lens assembly A 2 produces the image of an object (c b a) in a non-inverted and nonmagnifying manner, as with the lens assembly A 1 .

As stated above, the grooves 14 in the lens assembly A 2 are provided only on one side of the third lens array 1 C. However, the cross talk of light is properly prevented in the lens assembly A 2 due to the appropriate depth of the grooves 14 . The fourth lens array 1 D is provided with no such grooves and no light shielding layer. However, light beams which would otherwise cause cross talk in the fourth lens array 1 D are shielded by the light shielding layer 15 of the third lens array 1 C and prevented from going into the fourth lens array 1 D.

As mentioned above, the diameter of the second lens surfaces 11 b of the third lens array 1 C is greater than that of the first lens surfaces 11 a , and the diameter of the second lens surfaces 11 f is greater than that of the first lens surfaces 11 e . The diameter of the second lens surfaces 11 b of the third lens array 1 C is equal to or greater than that of the first lens surfaces lie of the fourth lens array 1 D. Thus, as seen from FIG. 16 , the incident light striking upon the first lens surfaces 11 a of the third lens array 1 C is properly led through the third lens array 1 C and the fourth lens array 1 D and finally to the focusing position F without unduly reducing the light intensity. Consequently, the resulting image (c b a ) becomes appropriately bright.

FIG. 17 shows a fifth lens array 1 E according to the present invention. As illustrated, the lens array 1 E is provided with a plurality of lenses 11 arranged in two parallel rows. In the respective rows, each of the lenses 11 is flanked by two grooves 14 as viewed from above ( FIG. 17 ) and from below (not shown). With such an arrangement, the lens array 1 E can generate a more brighter image than a lens array provided with only one row of lenses. With the use of a single lens array, an inverted and reduced image is obtained. Two lens arrays with one mounted on the other can produce a non-inverted and non-magnified image.

FIG. 18 shows a sixth lens array 1 F according to the present invention. The illustrated lens array 1 F is provided with a matrix of lenses 11 , which is suitable for producing a two-dimensional image. An identical lens array may be mounted on the lens array 1 F to provide a non-inverting and non-magnifying lens assembly. According to the present invention, the number and arrangement of the lenses 11 may be varied.

According to the present invention, each lens may have two opposed lens surfaces which are both convex or both concave. In certain applications, only one of the lens surfaces may be convex or concave, while the other lens surface may be flat. In such an instance, the flat lens surface may not be covered by a surface-smoothing transparent layer. A concave lens array may be used in combination with a concave lens array to provide a lens assembly which does not suffer from chromatic aberration.

According to the present invention, the transparent layer for smoothing out a surface may not be completely clear. As long as proper light passage is not hindered, the transparent layer may be colored.

The present invention is applicable not only to a lens array or lens assembly but also to a single lens. FIG. 19A shows a convex lens 9 whose lens surfaces 90 are covered by a transparent layer 16 . FIG. 19B shows a concave lens 9 a whose lens surfaces 90 a are covered by a transparent layer 16 a.