Abstract: An infrared optical system for infrared cameras has a convex lens held by a holding member composed of a low-dispersion material that transmits infrared light. A stop for restricting light beams entering the convex lens is disposed on an object side from the convex lens. An aberration correcting plate for reducing spherical aberration is provided in the vicinity of the stop. A field flattener, the thickness of which changes along image height to offset curvature of field, is disposed on an image side of the convex lens.

Abstract: A standard photographic lens is disclosed that includes a front lens group, a diaphragm stop, and a rear lens group, in order from the object side. The front lens group is formed of a negative meniscus lens with its convex surface on the object side, and a positive meniscus lens with its convex surface on the object side. The rear lens group is formed of a third lens element of negative refractive power with a concave surface on the object side, a fourth lens element of positive refractive power with a convex surface on the image side, and a fifth lens element, of meniscus shape with its concave surface on the image side. Organic material is preferably used for the second and third lens elements. Various conditions are satisfied so as to provide a lens having a bright image with favorably corrected aberrations.

Abstract: An iris type light quantity adjusting device is disclosed that includes:

Abstract: A CO2 laser beam 12 is converted into a beam of uniform intensity at the position of a phase matching element 15 by an intensity converting element 14 and the phase matching element 15. Then, the uniform intensity beam irradiates a mask 17 containing an aperture variable in size via a variable-magnification projecting optical system 16. At the time of irradiation, the laser beam at the position of the phase matching element 15 is projected onto the mask 17 at a magnification factor most suited to the size of the aperture formed in the mask 17. Further, the pattern of the mask 17 is projected onto a workpiece 19. Thus, a uniform intensity distribution of the laser beam is obtained on the workpiece and high quality laser processing becomes possible.

Abstract: A variable focal length lens system comprising a first lens group G1 having a positive refractive power, a second lens group G2 having a positive refractive power and a third lens group G3 having a negative refractive power from the side of an object in this order; the respective lens groups are moved toward the object side in such a manner that, when the lens positional state is changed from a wide angle end state to a telephoto end state, a distance between the first lens group G1 and the second lens group G2 is increased and a distance between the second lens group G2 and the third lens group G3 is decreased; an aperture stop S is disposed in the vicinity of the second lens group G2; the aperture stop is moved together with the second lens group G2 in response to a change in the lens positional state so that the third lens group G3 is composed of a positive lens with the convex surface facing the side of an image and a negative lens which is disposed away from the positive lens with an air distance therebe

Abstract: A flexible lens is provided that comprises at least two chambers encased by a flexible membrane and separated by a partition, wherein pressure within the chambers is regulated such that when one chamber receives positive pressure, the other chamber receives negative pressure. Accordingly, a first lens portion and a second lens portion of the flexible membrane flex in the same relative direction when the pressure is regulated. In addition, a variable optical input such as an iris diaphragm is provided that operates in concert with the flexible membrane. As a result, the flexible lens generates a constant spot size output having a substantially flat intensity distribution and a substantially uniform angular distribution. Similarly, the flexible lens generates a variable spot size output having a substantially flat intensity distribution and a substantially uniform angular distribution when the optical input is constant.

Abstract: A retro-focus-type camera lens is disclosed that is formed of, in order from the object side: a front lens group having negative refractive power, a diaphragm, and a rear lens group having positive refractive power. The front lens group is formed of, in order from the object side, a positive lens element and two negative lens elements, and the rear lens group is formed of, in order from the object side, a positive lens element, two sets of lens elements that are cemented together to form two joined lenses, and a positive lens element. Various conditions are preferably satisfied in order to provide a lens having an image angle of about 38°, an F number of about 1.4, and which suppresses the occurrence of color shading while providing a sufficient back focus to insert a color separation optical system between the retro-focus-type camera lens and the image plane.

Abstract: An iris diaphragm, in particular for an exposure lens in semiconductor lithography, is provided with a diaphragm base (2) and a grooved ring (1) which can be rotated relative to one another, having a multiplicity of leaves (4) which in each case are mounted in the diaphragm base (2) and in the grooved ring (1) and are guided by curved tracks (6), arranged in the grooved ring (1), for the purpose of adjusting the diaphragm aperture. A drive device (11) serves the purpose of twisting the diaphragm base (2) and grooved ring (1) relative to one another. The curved tracks are designed as circumferential tracks (6) in the grooved ring (1). The circumferential track (6) is split up into alternating useful-region curves (6a) and return curves (6b). The diaphragm base (2) or the grooved ring (1) can be rotated in a preselected rotary drive direction by a drive device (11), the leaves (4) being guided in a circulating fashion in the circumferential track (6).

Abstract: A zoom lens system including a negative first lens group, a positive second lens group, and a negative third lens group. zooming is performed by moving the first through third lens. The negative first lens group includes positive-negative cemented lens elements, and the most object-side surface thereof is a concave surface. The zoom lens system satisfies: −1<r1/fW<0 . . . (1); 1.4<f1G/f1N<1.8 . . . (2); wherein r1: the radius of curvature of the most object-side surface of the first lens group; fW: the focal length of the entire zoom lens system at the short focal length extremity; f1G: the focal length of the first lens group; and f1N: the focal length of the lens element of the cemented lens elements.

Abstract: The present invention provides a bright image reading lens coping with high resolution and yet having a great depth of focus and a wide angle of field, and an image reading apparatus using the same. The image reading lens includes, in succession from the object side, six lenses, i.e., a meniscus-shaped positive first lens having its convex surface facing the object side, a second lens of which the both lens surfaces are concave surfaces, a third lens of which the both lens surfaces are convex surfaces, a meniscus-shaped fourth lens having its concave surface facing the object side, a meniscus-shaped negative fifth lens having its concave surface facing the object side, and a meniscus-shaped negative sixth lens having its concave surface facing the object side, and satisfies a predetermined condition.

Abstract: There are provided a zoom lens system comprising, in order from a more distant conjugate point, a first lens unit of a negative refractive power, a second lens unit of negative refractive power which moves during zooming, third, fourth and fifth lens units, and at least one diffraction optical element.

Abstract: An optical system includes a diffractive optical element in which a phase given to incident light from an optical axis toward the peripheral part in the radial direction is not reversed in an effective area and an absolute value of optical power on the optical axis is made minimum. In the optical system, chromatic aberration of magnification of a high order is satisfactorily corrected and flare caused by additional diffraction light (unnecessary diffraction light) is suppressed to as minimum as possible while maintaining a high imaging performance up to peripheral part of a field angle.

Abstract: An optical imaging device, in particular a lens system, has a system diaphragm (1). An aperture of the system diaphragm (1) is adjustable in its opening diameter (D). The axial position of the aperture of the system diaphragm (1) with respect to the optical axis (4) of the system diaphragm (1) is fixed in dependence on the opening diameter (D) of the system diaphragm (1).

Abstract: A zoom lens system includes a positive first lens group, a negative second lens group, a positive third lens group, and a positive fourth lens group. Upon zooming from the short focal length extremity to the long focal length extremity, at least the first, second and third lens groups are moved so that the distance between the first and the second lens groups increases, the distance between the second and the third lens groups decreases, and the distance between the third and the fourth lens groups increases.

Abstract: A lens assembly particularly suited to use with high resolution digital cameras suitable for incorporation in compact portable electronic devices such as cellular telephones, portable digital assistants and the like. The lens assembly includes a distal meniscus lens element formed from glass, and first and second, aberration correcting, aspheric lens elements formed from plastic, such as an acrylic, and positioned proximal to the meniscus lens element. An aperture stop plane is provided just in front of the front group. A fixed aperture stop or a combined variable aperture and shutter device may be positioned at the aperture stop plane.

Abstract: A zoom lens system has, sequentially from enlarging side to reducing side, first lens unit having negative optical power; second lens unit having positive optical power, the second lens unit having a positive lens element positioned nearest the reducing side; diaphragm; third lens unit having positive optical power, the third lens unit comprising, sequentially from enlarging side to reducing side, a cemented lens unit having a positive lens element and a negative lens element with a concave surface facing the reducing side, and a positive lens element having a concave surface facing the reducing side; fourth lens unit having negative optical power; and fifth lens unit having positive optical power. The second, third, and fourth lens units move from enlarging side to reducing side when zooming from telephoto end to wide angle end. The zoom lens system satisfies a predetermined condition.

Abstract: An aperture and lens mechanism for a camera, includes a rotatably mounted lens barrel supporting a lens and moveable in a direction parallel to the optical axis of the lens in response to rotation; an aperture support mounted for movement parallel to the optical axis of the lens and spring biased into contact with the lens barrel for movement therewith; and an aperture blade defining an aperture, the aperture blade being mounted on the aperture support for movement between a first position where the aperture is centered on the optical axis of the lens and a second position away from the optical axis of the lens.

Abstract: An image pickup lens system according to the present invention includes a lens body having a positive power and a diaphragm which is unified with the lens body at a location between the first face and the second face of the lens body and of which inner cylindrical surface is disposed at a location of the inside of the lens body. Thus, the numbers of the elements of the image pickup lens system are decreased and the image pickup lens system can be produced accurately. Moreover, when the lens body and the diaphragm are unified each other, both optical axes of the lens body and the diaphragm can be very accurately adjusted and automatically adjusted. Thus, a work to adjust accurately those optical axes is not necessary so that the lens body and the diaphragm can be produced easily and speedy. Moreover, by disposing the actual diaphragm, this invention can prevent the occurrence of the stray light such a flare and a ghost and the like and can actually remove the stray light if it occurs.

Abstract: An optical device for eliminating the stray light is provided at a stop of an illuminating system in an optical system of “digital light processing” (DLP). The optical system consists of a stop of an illuminating system, a “digital micromirror device” (DMD), a stop of a projection lens, and a screen while the stray light is a chromatic halo at the peripheral area on the screen. Wherein, the optical device includes a reflecting mirror designed of an adjustable angle and installed near periphery of the stop of the illuminating system. The chromatic halo is generated from the light beam at the periphery area. And, the light beam is reflected from the DMD and is transmitted into the stop of the projection lens, and then is projected on the screen.

Abstract: The object of the present invention is to provide a zoom lens system with a zoom ratio of seven or more suitable for compactness capable of obtaining stable optical performance in spite of reducing the number of lenses. According to one aspect of the present invention, a zoom lens system includes, in order from an object, a first lens group G1 having positive refractive power, a second lens group G2 having negative refractive power, a third lens group G3 having positive refractive power, and a fourth lens group G4 having positive refractive power. When the state of lens group positions of the zoom lens system is changed from a wide-angle end state to a telephoto end state, each lens group is moved to the object side such that the separation between the first lens group G1 and the second lens group G2 increases, the separation between the second lens group G2 and the third lens group G3 decreases, and the separation between the third lens group G3 and the fourth lens group G4 decreases.

Abstract: It is an object of this invention to provide a zoom lens capable of projecting an original projection image displayed by a liquid crystal display element onto a screen surface with high optical performance, and an image projection apparatus using the zoom lens. A zoom lens includes a first lens unit having negative refractive power, a second lens unit having positive refractive power, a stop, a third lens unit having negative refractive power, a fourth lens unit having negative refractive power, and a fifth lens unit having positive refractive power, which are sequentially arranged from the enlargement side and having one or a plurality of lenses. When the magnification is to be changed from the wide angle end to the telephoto end, the second, third, and fourth lens units and the stop move.

Abstract: A wide-angle projection lens is disclosed having three lens groups of negative, positive, and positive refractive power, respectively, in order from the enlarging side, and that favorably corrects both distortion and lateral color. The wide-angle projection lens includes a diaphragm positioned between the second lens group and the third lens group, and is especially suitable for use in a rear-projection-type image display device that uses a multi-display technique wherein multiple projection lenses arranged in an array, with each projection lens displaying image information for a particular segment of the image to be displayed. By satisfying specified conditions, the wide-angle projection lens, when used in a projection-type image display device, enables the image display device to be more compact.

Abstract: A zoom lens includes a first lens band having a positive focal length, a second lens band having a negative focal length, and at least third to fifth lens bands having positive focal lengths. An aperture diaphragm is located in the vicinity of the third lens band. When magnification i.e., zooming is performed from short to long focal point ends, the second lens band smoothly moves toward the third lens band and the fourth lens band simultaneously moves from the fifth lens band side toward a long focal point end so as to share a magnification function together with the second lens band.

Abstract: An optical device for eliminating the stray light is provided at a stop of an illuminating system in an optical system of “digital light processing” (DLP). The optical system consists of a stop of an illuminating system, a “digital micromirror device” (DMD), a stop of a projection lens, and a screen while the stray light is a chromatic halo at the peripheral area on the screen. Wherein, the optical device includes a reflecting mirror designed of an adjustable angle and installed near periphery of the stop of the illuminating system. The chromatic halo is generated from the light beam at the periphery area. And, the light beam is reflected from the DMD and is transmitted into the stop of the projection lens, and then is projected on the screen.

Abstract: An optical apparatus includes a first movable optical member, a second movable optical member, different from the first optical member, and a driving mechanism engaged with the second optical member, and operable in a first operation mode, in which the second optical member is movable by an electrical driving operation of the driving mechanism, and a second operation mode, in which the second optical member is movable by a manual driving operation. Operation of the driving mechanism is switched between the first operation mode and the second operation mode by control means such as a CPU, wherein, when the driving mechanism is operable in the second operation mode, the control means switches operation of the driving mechanism to the first operation mode in response to a driving operation of the first optical member.

Abstract: An optical scanning device according to the present invention includes a lens to convert divergent rays from a laser diode to parallel or convergent rays, a slit to regulate luminous energy of the parallel or convergent rays, a before deflection optical system having lenses with different power for main-scanning and sub-scanning, optical scanning means to scan objects to be scanned with the parallel or convergent rays, and an imaging optical system for imaging on the objects to be scanned by passing the scanned rays with the optical scanning means, the slit of the before deflection optical system has an opening with a larger diameter than a 13.5% diameter of the optical intensity of the rays in at least one direction of the main-scanning and the sub-scanning directions. Thereby, it may be possible to reduce the sidelobe, and to control density irregularities of exposed images.

Abstract: An imaging optical system having superior optical performance with the improved correction of chromatic aberration over a wide wavelength range extending from the visible wavelength range to the infrared wavelength range is provided. According to one aspect, an imaging optical system includes, in order from an object, a front lens group GF with a positive refractive power having at least one lens element, an aperture stop SP and a rear lens group GR with a positive refractive power having at least one lens element. The front lens group GF includes a double convex positive lens GT arranged to the most object side. At least one of the front lens group GF and the rear lens group GR includes a triple cemented lens GS being adjacent to the aperture stop SP having a negative refractive power as a whole composed of a first positive lens, a negative lens, and a second positive lens. Predetermined conditional expression is satisfied.

Abstract: A zoom optical system suited for use in an electronic image pickup apparatus comprising a first negative lens unit, a second positive lens unit and a third positive lens unit, in which a magnification is changed from a wide position to a tele position by moving at least the first lens unit and the second lens unit so as to change an airspace between the first lens unit and the second lens unit and widen an airspace between the second lens unit and the third lens unit, the second lens unit comprises a biconvex lens element and a cemented meniscus lens component having a convex surface on the object side, and each lens unit has a small thickness.

Abstract: A technique for increasing the lifetime of optical components that are used in a laser for laser shock peening. The technique employs a properly sized iris or a gradient reflector within a laser oscillator to produce a single-transverse-mode laser beam. This technique eliminates hot spots that significantly reduce the lifetime of optical components. Utilization of the present invention can increase the lifetime of components by a factor of ten of their conventional lifetime.

Abstract: A lens system has a plurality of lenses, a stop, and a diffractive surface, the entire lens system moves during focusing, and the lens system satisfies the condition of &bgr;≧0.5, where &bgr; is a maximum photographic magnification.

Abstract: A light-source device comprising: a rod integrator having an injection end and an emitting end; a lens unit for collecting a luminous flux emitted from the emitting end; and, a diaphragm. The rod integrator forms a plurality of imaginary light-source points, each of which virtually emits the luminous flux toward the emitting end. The diaphragm is disposed in the vicinity of a plane on which the lens unit forms the images of the imaginary light-source points, and selectively blocks luminous flux emitted from each of the images of the imaginary light-source points.

Abstract: A diaphragm structure is provided at an outer edge portion on an incident side of a lens which converges a collimated incident light and outputs the converged light, the diaphragm structure being constructed so that a portion of the collimated incident light is reflected away from or toward an optical axis of the collimated light.

Abstract: The invention relates to an endoscope lens which shows only a low level of distortion even at large angles of sight and whose elements can be produced and assembled with little effort, consisting of a first lens group having negative total refractive power, of an aperture diaphragm, and of a second lens group having a positive total refractive power, whereby all lens surfaces are spherical and all lenses are made of homogeneous materials. The first lens group contains at least one positive lens which is primarily arranged in the beam direction, and at least one negative lens, whereby the negative lenses in the first lens group are biconcave or plano-concave lenses. The invention also relates to an endoscope equipped with a lens of this type.

Abstract: A zoom lens comprises a first lens group having a positive focal length, a second lens group having a negative focal length, an aperture stop member, a third lens group having a positive focal length, disposed in the stated order from an object. The first lens group includes a 1-1 negative meniscus lens having a convex surface facing the object, a positive 1-2 lens having a surface having a large curvature facing the object and joined to the 1-1 lens, and a positive meniscus 1-3 lens having a convex surface facing the object, disposed in the stated order from the object. A reflection preventing part is formed on a surface at which the 1-1 lens and the 1-2 lens are joined.

Abstract: A lens system has the first and second lens elements from the object side. The first lens element has a negative optical power. The second lens element has a positive optical power. The lens system fulfills the conditions: 0.0<PRL/Y′<0.5, 0.5<Pf/f<1.0. In the conditions, PRL represents a distance in a direction perpendicular to the optical axis between the optical axis and an incident position where a lower ray of a most off-axial rays enters said second lens element, Y′ represents a largest image height, f represents a focal length of the entire lens system, and Pf represents a focal length of said second lens element.

Abstract: A taking lens comprises a first meniscus lens opposing its convex surface to an object side and a second lens having a positive power. An image side surface of the first lens and an object side surface of the second lens are aspherical.

Abstract: A zoom lens comprises a first lens unit having positive refractive power, a second lens unit having negative refractive power, an aperture stop, a third lens unit having positive refractive power and kept fixed during zooming, a fourth lens unit having positive refractive power, and a fifth lens unit having negative refractive power, which are arranged in this order from an object side. In zooming from a wide-angle end to a telephoto end, the second lens unit is moved toward an image plane side such that a spacing between the first lens unit and the second lens unit is increased, and the aperture stop is also moved.

Abstract: A lens assembly particularly suited to use with high resolution digital cameras suitable for incorporation in compact portable electronic devices such as cellular telephones, portable digital assistants and the like. The lens assembly includes a distal meniscus lens element formed from glass, and first and second, aberration correcting, aspheric lens elements formed from plastic, such as an acrylic, and positioned proximal to said meniscus lens element. An aperture stop plane is provided just in front of the front group. A fixed aperture stop or a combined variable aperture and shutter device may be positioned at the aperture stop plane.

Abstract: A photographing lens of a camera comprises a non-circular lens and a light blocking mask. The non-circular lens receives an optical image from an object and forms an image on a photographing medium. The light blocking mask is fixed in front of the non-circular lens, and blocks noise light generated in relation to the non-circular lens.

Abstract: A fixed making frame for blocking the peripheral light is disposed between a taking lens aperture and an exposure frame of a film surface. The effective diameter of the taking lens aperture is variable so as to make an angular field of a photogtaphing light which extends from the taking lens aperture to an exposure area. The angular filed is smaller under a larger effective diameter than under a smaller effective diameter. A predetermined width of a periphery of the exposure area defines a non-print area, and the fixed making frame is disposed at a side adjacent to the taking lens aperture with respect to an intersection of the peripheral light which extends between an inner periphery of the non-print area and the lens aperture under a larger effective diameter of the taking lens, and a peripheral exposure light which extends the lens aperture and an outer periphery of the exposure area, under a smaller effective diameter of the taking lens aperture.

Abstract: A multiple element color-corrected doubly telecentric lens and imaging system useful for imaging multiwell plates is described. The lens contains a biconvex field lens element L1, a positive meniscus lens element L2, concave toward the incident light side, a double-Gauss lens element group, a positive meniscus lens element L10, convex toward the incident light, a positive meniscus lens element L11, convex toward the incident light, and a plano concave field flattener lens element L12, concave toward the incident light side. The lens is very sensitive, and can be used to image scintillation proximity assays in multiwell plates.

Abstract: A variable focal length lens system includes at least three lens groups, in order from an object side, a first lens group G1, a second lens group G2, and a third lens group G3. When the lens group positions are changed from a wide-angle end state to a telephoto end state, each lens group moves from a state focused at infinity to a state focused at near object, in order from a state focused at infinity in the wide-angle end state to a state focused at near object in the telephoto end state. G2 has an aperture diaphragm S, and lens elements are arranged to both object and image side of the aperture diaphragm S.

Abstract: A Gaussian lens having no more than six lens elements of refractive power is formed of, in order from the object side: a first lens element which is biconvex, a second lens element which is a positive meniscus lens with its convex surface on the object side, a third lens element which is biconcave, a stop, a joined lens formed of a fourth lens element which is biconcave that is joined to a fifth lens element which is biconvex; and a sixth lens element having positive refractive power. Specified conditions are satisfied in order to provide a compact lens having an f-number FNO of 1.44 or less, an image angle 2&ohgr; of 23.8 degrees or more, and wherein the various aberrations are favorably corrected. The Gaussian lens of the invention is intended for mounting in monitor cameras.

Abstract: The improved inner-focus, wide-angle lens system of retrofocus configuration comprises, in order from the object side, a negative first lens group 10, a positive second lens group 20, and a positive third lens group 30 having a diaphragm; the second lens group 20 moves along the optical axis during focusing and the lens system satisfies the following conditions (1) and (2):

Abstract: An imaging optical element is comprised of a gradient index rod lens 12 of which external peripheral surface is a smooth surface without being processed by means of a flare-cut treatment and a field limitation stop member 14 mounted on the lens surface at the incidence side thereof. As for the stop member, the length t thereof is: t>lo·D/2X (where, lo: a lens working distance, D: a rod lens diameter, X: a radius of field of view), whereby the angle of incidence of beam &thgr; at the center of the lens satisfies &thgr;<tan−1(X/lo). It is effective especially when an application thereof is made to a rod lens array comprised of a plurality of rod lenses arranged into an array.

Abstract: A lens assembly particularly suited to use with high resolution digital cameras and other portable electronic devices. The lens includes a positive powered front group having one or two elements and a second, aberration correcting, rear group having in order from the front a bi-concave element, a meniscus element and a bi-concave element. The aperture stop plane is just in front of the front group. A combined operator and shutter device is positioned at the aperture stop plane. All of the lens elements are made of glass and have spherical surfaces.

Abstract: An auxiliary imaging lens is attachable to the main part of zoom lens on the object side; and is configured such that, when capturing an image for a screen having an aspect ratio of 4:3, an effective imaging area having such a size that the screen having an aspect ratio of 4:3 in a case without using the auxiliary imaging lens is just held therein can be secured, and a focal length yielding a field of view area substantially on a par with a field of view area obtained when capturing an image for a screen having an aspect ratio of 16:9 can be set.

Abstract: In an image-forming lens, an inclined slope or section is provided at a marginal annular region on a surface of an optical member and a light shield is provided on this inclined slope or section. The optical member is mounted longitudinally so that the inclined slope or section is located near where off-field fight (i.e, fight from outside the designed field of view of the lens) reflects off an inner surface of a holding member or at the periphery of an optical member. Thus, the inclined slope or section with light shield acts to shield the reflected off-field light from passing to the image. The invention finds particular advantage in very small lenses that include optical members less than 3 mm in diameter.

Abstract: A lens barrel including an iris stop unit which is easily secured in the lens barrel. The lens barrel includes a lens group holding frame fixed by screws to a moving tube which holds a lens group in a manner freely slidable in a forward or backward direction. A support ring is formed integrally with the moving tube, and the support ring, along with blades and a drive ring forms an iris stop unit. The blades and the drive ring are set at a designated position and the lens group holding frame is inserted into the moving tube and connected by screws. The drive ring is held by the front end of the lens group holding frame.

Abstract: An optical pickup device for condensing the light from a light source on a signal recording surface by an objective lens and for detecting the return light from the signal recording surface by a light detection unit is disclosed. The optical pickup device is capable of recording and/or reproducing at least two different sorts of optical recording media. The light beam radiated from a light source is condensed by an objective lens. An aperture varying unit varies the size of an aperture of the objective lens depending upon the sorts of the optical recording media. The return light from the optical recording medium is detected by a light detection unit. The size of the aperture of the objective lens for condensing the light from the light source is varied depending upon the difference in substrate thickness of the different sorts of the optical recording media, thus assuring high-quality recording/reproduction for two or more different sorts of optical recording media.