A lens is formed in a generally rectangular shape, and a reflection-preventing portion capable of preventing reflection of harmful rays is provided on at least one edge plane forming at least a portion of the perimeter of the lens, so that the lens is capable of suppressing deterioration of the quality of images including object images formed by a photographic lens system, in order to obtain better photographic images.

BACKGROUND OF THE INVENTION
 1. Field of the Invention
 The present invention relates to a lens, and particularly relates to lenses
 making up a photographic lens system used for photography and the like,
 having reflection preventing means for preventing harmful rays.
 2. Description of the Related Art
 Photographic lens systems which are used for photography with a photography
 apparatus such as a camera for forming an image of an object are generally
 comprised of a plurality of lenses and the like. The front surface of each
 of such lenses making up the photographic lens system is generally round.
 In the event that a portion of incident light rays to such a photographic
 lens system reflects off of the edge of the lens, i.e., the inner surface
 of the perimeter rim, the reflected rays may be cast into the range of the
 photographic aperture. In the case that such reflected light reaches the
 formed image, this can cause blurring or ghosting, for example, which
 consequently has a negative effect on the object image and deteriorates
 the image quality of the photographed image.
 In order to suppress harmful rays which cause blurring and ghosting, known
 arrangement involve measures such as coating the edge plane of the lens
 with a black color or the like, providing a groove or the like in a
 direction orthogonal to the optical axis of the edge plane, and so forth,
 thereby suppressing generation of harmful rays.
 On the other hand, the shape of the aperture for forming a photographic
 image is generally rectangular, with photography apparatuses such as
 cameras and the like. In accordance with this, various photographic lens
 systems using a lens formed by cutting away portions unnecessary for image
 formation, i.e., portions other than the effective area of the lens
 corresponding with the photographic screen, are proposed in Japanese
 Unexamined Patent Publication No. 4-177301, for example.
 This arrangement aims to reduce the overall size of the lens system without
 narrowing the effective area of the lens to the photographic screen, by
 forming the front surface of the lens in a rectangular shape so as to
 correspond with the photographic screen (photographic aperture).
 However, in the event that a part of the perimeter of the lens is cut away,
 as represented by the means disclosed in the above Japanese Unexamined
 Patent Publication No. 4-177301, the edge of the perimeter (i.e., the cut
 plane) of the lens is closer to the optical axis of the lens as compared
 to the lens before cutting.
 This effect translates into an increase in the ratio of incident light rays
 to the lens system reflecting off of the edge of the perimeter of the lens
 and cast into the range of the photographic aperture so as to reach the
 formed image as harmful rays. This is problematic, since it has markedly
 adverse effects on and deteriorates the photographic image.
 This will be described in further detail, with reference to FIG. 33 and
 FIG. 34 of the drawings attached to the present Application.
 FIG. 33 is a lens configuration diagram illustrating the main cross section
 of a common photographic lens system comprised of multiple lenses. The
 optical path of a portion of the incident rays of the object light flux
 cast into this photographic lens system is shown.
 FIG. 34 is a lens configuration diagram illustrating the main cross section
 of a photographic lens system wherein a portion of the perimeter of a part
 of the lenses in the photographic lens system shown in FIG. 33 has been
 cut away and re-configured. The incident rays cast into this photographic
 lens system, and the optical path of the harmful rays caused thereby are
 shown. In this FIG. 34, the portion indicated by the dotted lines
 (reference numeral 105) represents the portion of lens that has been cut
 away.
 In a normal photographic lens system, light flux from the object or the
 like cast into the photographic lens system 101 as shown in FIG. 33, upon
 passing through the shutter/diaphragm mechanism 104 and the like without
 obstruction, follows a path such as shown by reference numeral 102 to
 reach a point X 101 on the same plane as the photographic aperture 103.
 The point X 101 shown here is a position out of the range of the
 photographic aperture 103. Accordingly, in the event that incident rays
 are cast into the photographic lens system 101 such as that shown by
 reference numeral 102, there is no effect on the image including the
 object image (photographic results) obtained upon being imaged behind the
 photographic aperture 103.
 Next, let us consider the case of the means disclosed in Japanese
 Unexamined Patent Publication No. 4-177301 and so forth, i.e., a
 configuration wherein a portion (shown by reference numeral 105 in FIG.
 34) of the perimeter of a part of the lenses in the photographic lens
 system shown in FIG. 33 has been cut away.
 In this case, the light flux from the object or the like cast into the
 photographic lens system 101A as shown in FIG. 34, upon passing through
 the shutter/diaphragm mechanism 104 and the like without obstruction,
 reflects off the edge plane 101Ab of the perimeter of the lens 101Aa at
 which part of the perimeter has been cut off, i.e., reflects off of the
 cut plane, and follows a path such as shown by reference numeral 102A to
 reach a point X 102 which is in the range of the photographic aperture
 103.
 The point X 102 shown here is a position in the range of the photographic
 aperture 103. Accordingly, the incident rays 102A become harmful rays
 which have adverse effects on the image including the object image
 obtained upon being imaged by the photographic lens system
 In this way, in the event that a part of the perimeter of the lens is cut
 away, the edge (i.e., the cut plane) of the lens is closer to the optical
 axis of the lens, so more harmful rays (reflected rays, etc.) are
 propagated. Accordingly, using such a photographic lens system for
 photography deteriorates the photographic image obtained as a result of
 the photography.
 However, the above Japanese Unexamined Patent Publication No. 4-177301
 discloses no means for suppressing such harmful rays. Accordingly, the
 means as disclosed caused problem of deterioration of the photographic
 image due to the above-described harmful rays.
 SUMMARY OF THE INVENTION
 Accordingly, it is an object of the present invention to provide a lens
 whereby the image quality of an image including an object image formed by
 a photographic lens system can be prevented from deteriorating, thereby
 obtaining even better photographic results (images).
 Briefly, according to the first aspect of the present invention, a lens is
 formed in a generally rectangular shape, wherein a reflection-preventing
 portion capable of preventing reflection of harmful rays is provided on at
 least the plane neighboring the optical axis of the edge planes.
 Also, according to a second aspect of the present invention, at least one
 lens of the lenses comprising a photographic optical system is arranged
 such that the perimeter of the lens has been removed except for the
 effective area of the lens corresponding with a photographic screen formed
 by a photographic aperture, and wherein a harmful ray suppressing portion
 capable of preventing reflection of rays from the edge of the lens at this
 removed portion is provided along this edge portion.
 These and further objects and advantages of the present invention will
 become clearer from the following detailed description.
 According to the present invention, providing a rectangularly formed lens
 and forming reflection preventing means or harmful ray-suppressing means
 capable of preventing reflection of incident light and suppressing the
 generation of harmful rays to the rectangularly formed lens, and using
 this lens in a photographic lens system, prevents deterioration of the
 image including the object image formed by this lens system, thereby
 providing a lens whereby photography results (images) can be obtained.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
 The following embodiments are examples of applying the lens according to
 the present invention to a photographic lens used by a camera for
 photography.
 As shown in FIG. 1, the photographic optical system (hereinafter referred
 to as "photographic lens system") 1 according to the present embodiment is
 configured as a plurality of lenses, and a shutter/diaphragm mechanism 4
 is provided at a certain position. Incidentally, the photographic lens
 system according to the present embodiment is a zoom lens with variable
 magnification, and FIG. 1 shows the focal distance of the zoom lens at an
 arbitrary distance.
 Now, regarding the photographic lens system for compact cameras and the
 like, there are arrangements wherein the lens system is configured as a
 telephoto-type lens system, in order to shorten the overall length of the
 lens system. With such photographic lens systems, the lenses in the rear
 group are generally of greater diameter than the lenses in the front group
 (see reference numeral 5 shown by dotted lines in FIG. 1, or FIG. 33).
 Accordingly, the size of this rear group increases the overall size of the
 photographic lens system, and this has been a factor impeding the
 reduction in size of photography apparatuses such as camera using the
 photographic lens system.
 Hence, with the photographic lens system 1 according to the present
 embodiment, of the plurality of lenses forming the photographic lens
 system 1 as shown in FIG. 1, the three lenses at the rear group have a
 portion of the perimeter thereof cut away, so that the cross-section
 thereof in the direction orthogonal to the optical axis is of a generally
 rectangular form. The portion that is cut away, i.e., the portion
 indicated by dotted lines in FIG. 1 (reference numeral 5) is the portion
 of each of the lenses other than the portion equivalent to the effective
 area of the respective lens corresponding to the image screen formed by
 the photographic aperture 3.
 Such an arrangement realizes a reduction in size of the photographic lens
 system 1 without narrowing the effective area of the lens with respect to
 the photographic screen.
 The object light flux cast into the photographic lens system 1 thus
 configured may become harmful rays upon following an optical path such as
 that indicated by reference numeral 2 in FIG. 1. That is, the incident
 rays 2 are cast into the front lenses of the photographic lens system 1,
 and upon passing through the shutter/diaphragm mechanism without being
 obstructed, reach the edge of the perimeter] of the lens 1a, i.e., the cut
 plane 1ab.
 Now, in the event that the incident rays reflect off of the cut plane 1ab
 as shown in the enlarged diagram FIG. 3, the reflected rays 2a become
 harmful rays which are cast into the range of the photographic aperture 3.
 To prevent this effect, means for suppressing these harmful rays are
 provided in the lens 1a of the photographic lens system 1 according to the
 present embodiment, to serve as reflection-preventing means and harmful
 ray-suppressing means for restricting reflection at the cut plane 1ab.
 The reflection-preventing means/harmful ray-suppressing means will now be
 described.
 As shown in FIG. 2, a black non-transmitting coat 6 is provided on the cut
 plane 1ab of the lens 1a, which is one of the lenses from which the
 perimeter has been cut away as shown in FIG. 1, to serve as the
 reflection-preventing means/harmful ray-suppressing means. This black
 non-transmitting coat 6 serves to absorb harmful rays cast on the cut
 plane 1ab of the lens 1a.
 In FIGS. 3 and 4, the reflected rays 2a and 2ab are distinguished by being
 represented by solid lines and dotted lines, respectively. In other words,
 the reflected rays 2ab indicated by dotted lines in FIG. 4 have been
 reduced by the black non-transmitting coat 6 as compared with the
 reflected light 2a shown in FIG. 3. FIGS. 3 and 4 thus demonstrate one
 mechanism by which generation of harmful rays which reach the range of the
 photographic aperture 3 can be suppressed.
 According to the first embodiment of the present invention, a black
 non-transmitting coat 6 is provided as a reflection-preventing
 means/harmful ray-suppressing means on the cut plane 1ab along the edge
 forming the perimeter of a lens in the photographic lens system 1, to
 thereby suppress the generation of harmful rays. Accordingly,
 deterioration of image quality of the photographic image including the
 object image which is formed by the photographic lens system 1 can be
 prevented, thereby obtained even better photographic results (images).
 Incidentally, this description has been made regarding only the lens 1a of
 the photographic lens system 1, but the cut planes 1ab of the other lenses
 at which the edges forming the perimeter has been cut away as described
 above have been subjected to the same reflection-preventing means/harmful
 ray-suppressing means, thereby forming reflection-preventing portions.
 Also, in order to simplify the FIGS. 3 and 4, refraction of rays at the
 border between the planes of the lens 1a and the air have been omitted in
 the illustration of incident rays 2 entering the lens 1a and harmful rays
 2a and 2ab exiting the lens 1a. This simplification is applicable to the
 descriptions regarding the other embodiments as well.
 Next, a second embodiment of the present invention will be described with
 reference to FIGS. 5 through 7. FIG. 5 is a perspective view of a relevant
 edge region of a lens according to this embodiment. FIG. 6 illustrates the
 optical path of harmful rays which can occur in this lens, and FIG. 7
 illustrates the incident rays cast into this lens and the optical paths of
 harmful rays which can be prevented by the reflection-preventing means
 provided in this lens.
 The overall configuration of the photographic lens system in which the lens
 of the present embodiment is included is generally the same as that in the
 first embodiment. Accordingly, the details thereof are omitted from the
 drawings, which would appear substantially the same as in FIG. 1.
 Also, the same reflection-preventing means/harmful ray-suppressing means of
 the lens according to the present invention may be applied to lenses of
 various forms, so the lenses described in the present embodiment and the
 following embodiments are each described as different examples of the
 various forms.
 The lens 1Aa according to the second embodiment has a portion of the
 perimeter thereof cut away, so that the cross-section thereof in the
 direction generally orthogonal to the optical axis is of a generally
 rectangular form. In the event that incident rays cast into this lens 1Aa
 are reflected at the cut plane 1ab, the reflected rays may be cast into
 the range of the photographic aperture 3, as shown in FIG. 6. This may
 result in the reflected rays 2a having adverse effects on the photographic
 image formed by the photographic aperture 3.
 Accordingly, the lens 1Aa of the present embodiment has
 reflection-preventing means achieved by surface processing to form
 extremely minute rough formations on the surface of the cut plane 1ab as
 shown in FIG. 5, i.e., a sand paper-like surface. According to this
 arrangement, in the event that incident rays are cast into the surface of
 the cut plane 1ab on which the roughened surfacing has been provided as
 the reflection-preventing means, the reflected light 2ab is scattered as
 shown in FIG. 7, so the reflected light 2ab does not converge at the same
 point on the plane of the photographic aperture 3.
 Thus, according to the present embodiment, the rays reflected by the lens
 1Aa can be scattered by roughening the surface of the cut plane 1ab,
 thereby reducing the effects of harmful rays. Accordingly, advantages
 similar to the above-described first embodiment can be obtained.
 Incidentally, the reflection preventing means shown with reference to the
 first embodiment (i.e., the black non-transmitting coat 6 on the cut plane
 1ab), and the reflection preventing means shown with reference to the
 second embodiment (i.e., the roughened surfacing on the cut plane 1ab) may
 be used in conjunction. Such an arrangement further suppresses harmful
 rays, and contributes to improvement in the photographed image.
 Next, a lens according to a third embodiment of the present invention will
 be described with reference to FIGS. 8 through 10.
 FIG. 8 illustrates a lens having edge regions according to the third
 embodiment. FIG. 9 illustrates the optical path of harmful rays which can
 be prevented by the reflection-preventing means/harmful ray-suppressing
 means provided in this lens. Also, FIG. 10, which is shown only for
 reference, is a diagram illustrating the optical path of harmful rays
 which would otherwise occur if a reflection preventing portion were not
 provided in a lens of the same form.
 The lens 1Ba according to the third embodiment also has a portion of the
 perimeter thereof cut away, as with the lenses 1a and 1Aa in the first and
 second embodiments, so that the cross-section thereof in the direction
 generally orthogonal to the optical axis is of a generally rectangular
 form. The cut plane 1ab of the lens 1Ba is provided with a groove 7 having
 a triangular cross-section in a direction generally orthogonal to the
 optical axis, as shown in FIG. 8, the groove 7 serving as a
 reflection-preventing portion.
 Now, in the case of a lens Baa in which the groove 7 constituting the
 reflection-preventing portion is not provided, the incident rays to the
 lens 1Baa reflect off of the cut plane 1ab. In this case, in the event
 that these reflected rays 2a reach within the range of the photographic
 aperture 3, these rays become harmful rays which cause deterioration of
 the photographic image formed by the photographic aperture 3.
 Accordingly, a groove 7 is provided as a reflection-preventing portion in
 the cut plane 1ab at the perimeter of the lens 1Ba according to the
 present embodiment (see FIGS. 8 and 9), thereby deflecting any harmful
 rays which may otherwise have adverse effects on the photographic image.
 In other words, as shown in FIG. 9, a portion of the incident rays 2 into
 the lens 1Ba have the direction thereof changed by the groove 7 at the cut
 plane 1ab, so as to follow an optical path such as the reflected light
 2ad, for example. As a result of the direction of the reflected light 2ad
 being changed by the groove 7, the reflected rays 2ad are cast out in a
 direction opposite to that of the photographic aperture 3, and
 accordingly, there are no adverse effects on the photographic image.
 Hence, according to the present embodiment, a groove 7 provided in the cut
 plane 1ab is used to cast a portion of the harmful rays generated by the
 lens 1Ba in a direction opposite that of the photographic aperture 3, so
 the amount of harmful rays reaching the range of the photographic aperture
 3 can be reduced. Thus, advantages similar to those of the first and
 second embodiments can be obtained.
 Now, in the present embodiment, there are reflected rays 2ac of the
 incident rays 2 cast into the lens 1Ba of which the reflection direction
 is not reversed. To eliminate this effect, providing at least one of the
 means discussed in the first and second embodiments, i.e., the black
 non-transmitting coat 6 on the cut plane 1ab and the roughened surfacing
 on the same cut plane 1ab, effectively suppresses the above reflected rays
 2acas well. This further contributes to the removal of the harmful rays.
 As described above, the first embodiment involves providing the black
 non-transmitting coat 6 on the cut plane 1ab of the lens 1a and the second
 embodiment involves providing the roughened surfacing on the cut plane 1ab
 of the lens 1Aa. Also, the third embodiment involves providing the groove
 7 in the cut plane 1ab of the lens 1Ba.
 Though these reflections-preventing means/harmful ray-suppressing means
 described with the above embodiments are each effective even when used
 individually, using these together even further suppresses the harmful
 rays generated by the cut plane 1ab.
 Specific examples include an arrangement wherein the black non-transmitting
 coat 6 and the roughened surfacing is provided on the cut plane 1ab, an
 arrangement wherein the black non-transmitting coat 6 is provided on the
 cut plane 1ab in which the groove 7 has also been provided, an arrangement
 wherein the roughened surfacing is provided on the cut plane 1ab in which
 the groove 7 has also been provided, an arrangement wherein the black
 non-transmitting coat 6 and the roughened surfacing is provided on the cut
 plane 1ab in which the groove 7 has also been provided, and so forth.
 Now, various types of the reflection-preventing means in the above third
 embodiment, i.e., a groove in the cut plane 1ab, may be envisioned. For
 example, FIGS. 11 through 16 show various forms which can be conceived
 when the angle of the sides of the groove are taken into consideration.
 FIGS. 11 through 16 are enlarged main cross-sectional views of a relevant
 portion, e.g., the lower half of the lens 1a, illustrating various forms
 of the groove 7 constituting the reflection preventing portion provided on
 the cut surface 1ab of the lens 1a. Each drawing illustrates the incident
 rays cast into each lens 1a, and the optical paths of the harmful rays
 which can be suppressed by the reflection-preventing portions (groove 7)
 provided in the lenses 1a.
 Generally classifying the forms of the grooves in the FIGS. 11 through 16,
 the examples shown in FIGS. 11, 12, 15, and 16 are cases wherein the
 angles of the sides of the groove have been formed in a non-symmetrical
 fashion, and the examples shown in FIGS. 13 and 14 are cases wherein the
 angles of the sides of the groove have been formed in a symmetrical
 fashion.
 Regarding the angle of the incident rays cast into the lenses 1a provided
 with these grooves, FIGS. 11, 13, and 15 illustrate incident rays at low
 angles, and FIGS. 12, 14, and 16 illustrate incident rays at high angles.
 Here, the term "low angle" indicates that the angle of the incident rays to
 the surface of the cut plane 1ab of the lens 1a is an acute angle, and the
 term "high angle" indicates that the angle of the incident rays to the
 surface of the cut plane 1ab of the lens 1a is an obtuse angle.
 As shown in FIGS. 11 through 16, a portion of incident rays cast into the
 lens 1a are cast out in a direction opposite to that of the photographic
 aperture 3, so the groove 7 of the various forms serves to suppress the
 harmful rays in an even more effective manner.
 Also, though the remainder of the incident rays reflect toward the
 photographic aperture and thus become harmful rays, these remaining
 harmful rays also can be suppressed by performing the surface processing
 or the like according to the above-described first and second embodiments
 to the cut plane 1ab.
 Now, in order to prevent the harmful rays which cannot be removed by the
 above third embodiment, or the groove 7 (reflection-preventing portion)
 shown in FIGS. 11 through 16, from having adverse effects on the
 photographic image, the angle of the groove 7 must be set so that the
 harmful rays capable of reaching the photographic aperture are minimized,
 by taking various items in consideration, such as the focal distance of
 the lens, the number of lenses making up the overall photographic lens
 system, and so forth.
 On the other hand, FIGS. 17 through 28 show various forms which can be
 conceived when the position of the grooves 7 provided to the cut plane 1ab
 is taken into consideration.
 FIGS. 17 through 28 are enlarged plan views of the lens 1a from a direction
 generally orthogonal to the optical axis, wherein multiple grooves 7 are
 provided as reflection-preventing members on the cut plane 1ab of the lens
 1a.
 Categorizing the various forms of the lens 1 a further, FIGS. 17 through 22
 are arrangements wherein multiple grooves 7 have been provided on the cut
 surface 1ab in a generally uniform manner, and FIGS. 23 through 28 are
 arrangements wherein multiple grooves 7 have been provided on the cut
 surface 1ab in a non-uniform manner.
 As shown in the Figures, the grooves serving as the reflection-preventing
 portion may be positioned on the cut plane 1ab so as to follow the lens
 plane of the lens 1a (see FIGS. 17, 21, 23, 25, 27), or intermittent
 grooves may be provided instead of continuous grooves (see FIGS. 19, 20,
 25, 26). Incidentally, there is a need for at least one of the grooves 7
 to cover the entire width in the direction orthogonal to the optical axis.
 Further, FIGS. 29 through 32 show various forms which can be conceived when
 the depth of the grooves provided in the cut plane 1a is taken into
 consideration.
 FIGS. 29 through 32 are enlarged main cross-sectional views of a relevant
 portion showing only the upper half of the lens 1a, wherein multiple
 grooves 7 have been formed in the cut plane 1ab of the lens 1a to serve as
 a reflection-preventing portion.
 Now, as shown in FIGS. 29 and 30, there are arrangements wherein the
 multiple grooves have all been formed to a uniform depth, and, as shown in
 FIGS. 31 and 32, arrangements wherein the multiple grooves have been
 formed to different depths, and so forth.
 With the grooves 7 of the various forms shown in FIGS. 25 through 32
 serving as examples, the position and depth of the grooves 7 must be set
 so that the harmful rays capable of reaching the photographic aperture are
 minimized. In forming the lenses in this manner, various factors are taken
 into consideration, such as the focal distance of the lens, the number of
 lenses making up the overall photographic lens system, and so forth.
 Incidentally, the grooves 7 formed in the lens 1a can be easily formed by
 general means, such as grinding the lens 1a with a grindstone, glass lens
 forming methods, plastic forming methods, and so forth.
 It is clear that a wide variety of different embodiments can be configured
 based on the present disclosure, without departing from the spirit or
 scope of the present invention.
 The present invention is by no means restricted in any way by any
 particular embodiments thereof, except as restricted in the attached
 claims.