Abstract: A projection exposure lens has an object plane, optical elements for separating beams, a concave mirror, an image plane, a first lens system arranged between the object plane and the optical elements for separating beams, a second double pass lens system arranged between the optical elements for separating beams and the concave mirror, a third lens system arranged between the optical elements for separating beams and the image plane. The second lens system has a maximum of five lenses.

Abstract: An imaging optical system includes a polarization beam splitter, a quarter waveplate, a reflection mirror and polarization state changing unit. The beam from an object plane is projected by way of the polarization beam splitter and the quarter waveplate to reflection mirror. The projected beam is reflected by the reflection mirror and is projected through the quarter waveplate and by way of the polarization beam splitter to an image plane, and the polarization state changing unit is disposed between the polarization beam splitter and the image plane to change the state of polarization of the beam projected by way of the polarization beam splitter. The polarization state changing unit includes a half waveplate effective to transform the beam projected by way of the polarization beam splitter into a rectilinearly polarized beam, being polarized in a desired direction.

Abstract: A projection exposure system for microlithography includes an illuminating system (2), a reflective reticle (5) and reduction objectives (71, 72). In the reduction objective (71, 72), a first beam splitter cube (3) is provided which superposes the illuminating beam path (100) and the imaging beam path (200). In order to obtain an almost telecentric entry at the reticle, optical elements (71) are provided between beam splitter cube (3) and the reflective reticle (5). Advantageously, the reduction objective is a catadioptric objective having a beam splitter cube (3) whose fourth unused side can be used for coupling in light. The illuminating beam path (100) can also be coupled in with a non-parallel beam splitter plate. The illuminating beam path is refractively corrected in passthrough to compensate for aberrations via the special configuration of the rear side of the beam splitter plate.

Abstract: An image reading apparatus includes a laser source, a stage on which an image carrier can be placed, a light detector for detecting light released from the image carrier, and an optical head for condensing the laser beam emitted from the laser source onto the image carrier and condensing light released from the image carrier to lead it to the light detector and being two-dimensionally movable parallel to the stage, and a perforated mirror formed with a hole at a center portion thereof, and fixed in a path of the laser beam so that the laser beam can pass through the hole and light released from the image carrier and condensed by the optical head can be reflected thereby in such a manner that a path of the light is branched off from the path of the laser beam.

Abstract: A conventional interleaver, based on a stack of waveplates, relies on the orientation and the birefringence of the waveplates to differentiate the polarizations of one set of channels from another, so that the one set of channels can be separated from the other. The present invention relates to a virtual waveplate that is used to replace a birefringent waveplate. A virtual waveplate imposes a phase delay between the extraordinary ray and the ordinary ray by separating one from the other and differentiating the actual path lengths taken thereby, before recombining them. An interleaver constructed with the virtual waveplates of the present invention can be substantially a-thermal and potentially chromatic dispersion free.

Abstract: An optical device comprises a dispersion element, a reflector, and an angle-to-offset (ATO) element. The angle-to-offset (ATO) element has optical power. The dispersion element is positioned in or near a focal plane of the ATO element and adapted to separate an input wavelength division multiplexed (WDM) light beam received from an input port of the optical device into two or more channel light beams. The reflector is positioned in or near a focal plane of the ATO element and arranged to receive the channel light beams from the dispersion element via the ATO element. The reflector is designed to reflect at least one of the channel light beams toward a respective output port of the optical device. With this arrangement, the dispersion element, reflector and ATO element cooperate to optically demultiplex the input WDM light beam.

Abstract: An optical system invention is interposed between a pupil plane and an image plane, and includes a first prism, a second prism, and a holographic element which is sandwiched between the first prism and the second prism and is cemented to these prisms. When a light beam traveling along the optical path connecting the pupil plane and the image plane through the optical system is called a first beam, the first prism has a 1-1 surface placed on the pupil side, combining the function of transmission with the function of reflection of the first beam; a 1-2 surface placed on the opposite side of the pupil with respect to the 1-1 surface; and a 1-3 surface placed on the image side, transmitting the first beam. The second prism includes a 2-1 surface having the same shape as the 1-2 surface and placed opposite thereto, transmitting the first beam at least twice, and a 2-2 surface placed on the opposite side of the pupil with respect to the 2-1 surface of the second prism, reflecting the first beam.

Abstract: A common corrective eyeglass lens blank and a common mirror, Plano or magnifying, are brought together in a “compact” (small sized) construction and assembly to provide the very thing long desired in mirrors and not elsewhere found—corrected vision and ample working room between the eyes and any lenses, at the same time, at reasonable cost, in an elegance of implementation.

Abstract: An optical assembly divides a single image into a plurality of images which are simultaneously projected onto a single sensor array. The optical assembly is arranged so that each of the plurality of images can be made to pass through a filter of a different type. For example a polarizing filter of a different orientation, or a filter which passes a different spectral band. In this way a single digital camera having a single chip sensor array can simultaneously receive multiple substantially identical images which have been acted on by different filters. This allows data capture from a single frame of a single camera to be used to perform stress analysis, or spectral analysis. This is particularly useful when high speed image capture is desired which contains stress or spectral data, because each frame captured from the sensor array contains multiple images which can be processed to obtain stress or spectral data.

Abstract: A catadioptric projection objective comprises an object plane, a physical beam splitter, a concave mirror, an image plane, a first objective part, a second objective part, and a third objective part. The first objective part is located between the object plane and the physical beam splitter. The second objective part is located between the physical beam splitter and the concave mirror, and includes at least two divergent lenses. The third objective part is located between the physical beam splitter and the image plane.

Abstract: A reflection and refraction optical system includes a polarization beam splitter, a concave mirror, a lens group and a quarter waveplate, wherein an additional waveplate is provided to transform S-polarized light from the polarization beam splitter into circularly polarized light.

Abstract: A catadioptric projection lens comprising a first lens group (G1) disposed along a first optical axis (16a), a mirror (18) which creates a second optical axis (16b), a beam splitter (20) which creates a third optical axis (16c), a second lens group (G2) including a concave mirror (L22) disposed along the third optical axis on one side of the beam splitter, and a third lens group (G3) disposed along the third optical axis on the side of the beam splitter. The first and third optical axes are parallel, a configuration which reduces aberrations arising from gravitational deformation of the lens elements, when the first and third axes are aligned with the direction of gravity.

Abstract: A catadioptric lens (10) comprising, along an optical axis (AX), a first lens group (L1) having an objectwise concave annular incident surface (SI) upon which light from an object is first incident, and a most imagewise lens surface (16). The catadioptric lens further includes an annular main mirror (MM) arranged imagewise of the first lens group and having an objectwise concave reflective surface (R1) that reflects light objectwise. A secondary mirror (MS) is located objectwise of the annular main mirror and has an imagewise convex reflective surface (R2) that reflects light imagewise. The first lens group has a glass optical path from the incident surface to the main mirror to the secondary mirror and to the most imagewise lens surface of the first lens group. The catadioptric lens may also include a second lens group L2 imagewise of the first lens group. The second lens group may include two or more lenses, and preferably includes a cemented doublet (L34, L35).

Abstract: It is an object to provide a high-performance and compact exposure apparatus which can perform a projection exposure operation with satisfactory optical performance by using a plurality of compact projection optical systems each capable of ensuring a sufficient working distance and having excellent imaging performance, while preventing a decrease in throughput even in a large exposure area. An exposure apparatus for projecting and exposing an image of a mask onto a plate while moving a mask and a plate has a first projection optical system and a second projection optical system each of which is real-size and both-side telecentric and forms the erect image of the mask on the plate. The first or second projection optical system has a refraction optical system having a positive refracting power, and a concave reflecting mirror for reflecting a light beam from the refraction optical system toward the refraction optical system.

Abstract: A catadioptric reduction projection optical system having a first lens unit having negative refractive power and widening a light beam from a reticle, a prism type beam splitter for transmitting therethrough a light beam from the first lens unit, a concave reflecting mirror for returning the light beam emerging from the beam splitter to the beam splitter while converging it, and a second lens unit having positive refractive power and converging the light beam returned to the beam splitter and reflected by the beam splitter, and forming the reduced image of a pattern on the reticle on a wafer.

Abstract: A device for creating a panoramic field of view comprises a first light passing incident surface which is a cylinder surface and a second incident surface which is a mirror surface onto which light passing through the first surface impinges. A third incident surface onto which light from the second incident surface impinges is provided and the third incident surface being an aspherical transmission surface. A recollimating element for presenting a pupil plane depiction of a panoramic field of view is also provided. Various embodiments may include single or double lens devices with a second lens provided for the purpose of recollimating light.

Abstract: A catadioptric reduction projection optical system having a first lens unit having negative refractive power and widening a light beam from a reticle, a prism type beam splitter for transmitting therethrough a light beam from the first lens unit, a concave reflecting mirror for returning the light beam emerging from the beam splitter to the beam splitter while converging it, and a second lens unit having positive refractive power and converging the light beam returned to the beam splitter and reflected by the beam splitter, and forming the reduced image of a pattern on the reticle on a wafer.

Abstract: A zoom lens system that is free from parallax, is compact, and offers excellent optical performance has, from the object side, a positive first lens unit, a negative second lens unit, a positive third lens unit, and a negative fourth lens unit. The zoom lens system has a half-prism between the second lens unit and the third lens unit so that a light beam having passed through the second lens unit is split by reflection.

Abstract: A catadioptric reduction optical system capable of imaging an object by scanning in a scanning direction. The system comprises, objectwise to imagewise, a first optical system, a beam splitter, and a second optical system arranged adjacent the beam splitter opposite the image side thereof. The second optical system includes at least one concave mirror. The system also includes a third optical system arranged adjacent said beam splitter imagewise thereof, an aperture stop, and a fourth optical system having positive refractive power. The third and fourth optical systems include a plurality of lens elements preferably comprising of at least two glass types for facilitating the correction of aberrations. The system is designed such that the beam splitter is of a practical size, while allowing for a suitable working distance on the image side, a large numerical aperture, and sub-quarter micron resolution in the ultraviolet wavelength range.

Abstract: A display rerouting apparatus reroutes a displayed image from an image source in a display module for providing a redirected angular visibility for the displayed image. In an illustrative embodiment, the display rerouting apparatus includes a base panel having a rectangular opening or widow for positioning atop of a display module in communication equipment, a rear panel having a one-way reflective mirror positioned in a rectangular opening in this rear panel, and a front panel having a two-way reflective mirror positioned in a rectangular opening in this front panel. Both the rear and front panels are respectively hingeably attached at their lower edges to the rear and front edges of the base panel for facilitating the use of the rerouting apparatus on different types of communication. In operation, the image from the display module is projected through the base of the apparatus onto the two-way reflective mirror.

Abstract: A catadioptric reduction projection optical system having a first lens unit having negative refractive power and widening a light beam from a reticle, a prism type beam splitter for transmitting therethrough a light beam from the first lens unit, a concave reflecting mirror for returning the light beam emerging from the beam splitter to the beam splitter while converging it, and a second lens unit having positive refractive power and converging the light beam returned to the beam splitter and reflected by the beam splitter, and forming the reduced image of a pattern on the reticle on a wafer.

Abstract: The light radiation beam emitted by a source of finite dimension, integrated in a transparent plate or in contact therewith, is initially reflected inside the plate by a first surface located on the side of the plate (3) which is more remote from the source. The reflected light rays pass through plate and are again reflected by a second surface having micro projections and then directed outwardly, according to a micro-telescope arrangement.

Abstract: A catadioptric optical system in which a first imaging optical system is constructed of a unidirectional optical apparatus which transmits outgoing light from a first plane in one direction only and a bidirectional optical apparatus for transmitting the light that enters and reflecting the same to form an interim image of the first plane. A light guide guides the light from the interim image to a second imaging optical system through which the interim image is reimaged on a second plane. The unidirectional optical apparatus has an optical axis and at least one lens movable along the optical axis.

Abstract: Catadioptric projection systems are disclosed for projecting an illuminated region of a reticle onto a corresponding region on a substrate. The systems are preferably used with ultraviolet light sources (e.g., 193 nm). The systems comprise a first imaging system, a concave mirror, and a second imaging system. The first imaging system comprises a single-pass lens group and a double-pass lens group. The single-pass lens group comprises a first negative subgroup, a positive subgroup, and a second negative subgroup. Light from the illuminated region of the reticle passes through the single-pass lens group and the double-pass lens group, and reflects from the concave mirror to pass back through the double-pass lens group to form an intermediate image of the illuminated region of the reticle. The light is then directed to the second imaging system that re-images the illuminated region of the reticle on the substrate.

Abstract: Catadioptric systems are disclosed that project a demagnified image of an object on a substrate. A first optical system substantially collimates a light flux from the object and directs the light flux to a beamsplitter provided with a reflecting surface. A second optical system comprising a concave mirror and a negative lens and having unit magnification receives the light flux from the beamsplitter and directs the light flux back to the beamsplitter. A third optical system then receives the light flux from the beamsplitter and forms an image of the object on the substrate. The catadioptric systems satisfy various conditions.

Abstract: A projection exposure apparatus achieves good imaging performance as securing a sufficient working distance. This projection exposure apparatus has a projection optical system for projection-transferring a real-size image of a first object onto a second object, which is disposed between the first object and the second object. This projection optical system has a cemented lens consisting of a plano-convex lens and a first negative meniscus lens, a second negative meniscus lens, and path-bending prisms for guiding light from the first object to the plano-convex lens and for guiding light from the concave mirror to the second object. The present invention is based on finding of appropriate ranges of refractive powers of the first and second negative meniscus lenses and appropriate ranges of Abbe numbers of glass materials for the first and second negative meniscus lenses.

Abstract: This invention provides a catadioptric optical system for achieving excellent imaging performance to obtain a resolution of quartermicron order. The catadioptric optical system is an optical system for transferring a reduced image of a pattern on a first plane onto a second plane and includes a beam splitter, an input lens group for guiding a light beam having a predetermined wavelength from the first plane to the beam splitter, an output lens group for guiding the light beam from the beam splitter to the second plane, a first concave mirror having an enlargement magnification, and a second concave mirror having a reduction magnification. The first concave mirror is arranged in an optical path of the light beam incident from the input lens group on the beam splitter and passing through the beam splitter to cause the passing light beam to be incident on the beam splitter again.

Abstract: A solid catadioptric lens (10) includes substantially planar input surface (14), primary concave mirror 18, secondary convex mirror (22) and substantially spherical exit surface (24). The lens is composed of solid material (12) chosen according to the particular imaging application in which the lens is to be used. Radiation enters lens through input surface (14), travels through solid material (12) and is reflected off of primary mirror (18). Radiation subsequently passes internally through solid material (12) and is reflected off of secondary mirror (22). Subsequent to being reflected off of secondary mirror (22), radiation (30) passes through solid material (12) and out of lens (10) through spherical exit surface (24) and onto detector array (34) for imaging purposes.

Abstract: A compact image display system in which the optical pathway is folded and thereby extended between the image source and the imaging optics of the system. The image display system may be used in place of computer or television screens, and may further be affixed to a frame so that it is wearable by a human user as either a monocular or binocular device.

Abstract: A catadioptric reduction objective has a concave mirror 19', a beam splitter 150' and several lens groups (100', 200'; 300', 400'). The system diaphragm 40' is mounted between beam splitter surface 15' and image plane 36' and especially within the last lens group 400'. NA=0.7; for UV, DUV; image side or both sides telecentric; also achromatized.

Abstract: There is provided an objective lens for focusing a subject light to form a real image on a predetermined focal plane, an eyepiece through which the real image is observed, and the first and second prism assemblies between the objective lens and the eyepiece for erecting an inverted image. The first and second prism assemblies are arranged at a predetermined distance away from each other such that the exit surface of the first prism assembly and the incident surface of the second prism assembly face each other across the focal plane. As a result, the dust on the whole surface of the prism assemblies and the like are made inconspicuous. Moreover, a visual field frame is provided on the focal plane, so that the visual field frame can be prevented from becoming out of focus and the border of the visual field can be seen clearly. Furthermore, a virtual image of a mark such as a target mark is formed in the Albada method.

Abstract: A catadioptric reduction projection optical system having a first lens unit having negative refractive power and widening a light beam from a reticle, a prism type beam splitter for transmitting therethrough a light beam from the first lens unit, a concave reflecting mirror for returning the light beam emerging from the beam splitter to the beam splitter while converging it, and a second lens unit having positive refractive power and converging the light beam returned to the beam splitter and reflected by the beam splitter, and forming the reduced image of a pattern on the reticle on a wafer.

Abstract: An optical apparatus monitors the entire panorama in low resolution and simultaneously monitors a selected portion of the panorama in high resolution. For the panoramic portion of the apparatus, a mirror having a convex surface of revolution with a hole therein is used. The higher resolution part of the apparatus uses a pointing mirror positioned above this hole. The panoramic and higher resolution views are imaged through lenses or optical components onto a detector. The panoramic view is imaged onto the detector as an annulus of light in which either higher or lower elevational angles of the panorama are imaged further away from the detector's center depending upon how the convex mirror is configured. In this way, the resolution of that portion of panorama that is imaged further away from the detector's center is enhanced. The higher resolution view is imaged to the center of the annulus.

Abstract: A multi-color optical display system (10) employs a multi-powered reflective combiner (20) that together with a monochromatic or partly color-corrected relay lens (16) longitudinally corrects a multi-colored image. The combiner typically includes two surfaces (82, 90) of different optical powers with a reflective coating (106, 108) on each of the surfaces. The coatings are chosen to each reflect a specific wavelength range of colored light used in the system and to transmit all other wavelengths. The curvature of each surface is dictated by the aberrations in the color image created by the relay lens. Specifically, each surface is positioned so that its focus (86, 94) coincides with the focal point (58, 60) of the corresponding color component in an intermediate image (18) created by the relay lens so that the final virtual image (22) reflected by the combiner is longitudinally color corrected.

Abstract: An optical guide (10, 40, 50, 60) for horizontally aligning two vertically stacked images generated by one or two SLMs. The optical guide has a channel separator (10a) that directs both images along two different paths. A pair of aligning reflectors (10b and 10c) on each path vertically shift the images with respect to each other so that at least part of the images on the first path are aligned side-by-side with at least part of the images on the second path. The channel separator (10a) then redirects the images to the image plane 15. Along both paths, at least two of the reflecting surfaces of channel separator (10a) or aligning reflectors (10b and 10c) are optically powered so as to change the width or height of the images.

Abstract: A catadioptric optical system includes a first imaging optical system forming an intermediate image of a pattern provided on a first surface with a reduced magnification, including a first lens group with a positive refracting power and a second lens group which includes a concave mirror having a negative lens component. The system also includes a second image optical system forming an image of the intermediate image upon a second surface, a combined magnification of the first and second imaging optical systems being a reduction magnification. The system further includes a deflecting member disposed in an optical path from the first imaging system to the second imaging system so as to guide light from the first imaging system to the second imaging system.

Abstract: This invention relates to a catadioptric optical system in which, a large numerical aperture is attained on the image side and, while securing a sufficient working distance, the size of the beam splitter is reduced, thereby attaining a resolution of a quarter micron unit, and an exposure apparatus using the same. In order to form a reduced image of a pattern of a first surface on a second surface, this catadioptric optical system comprises, at least, a first lens group, a beam splitter, a concave mirror having an enlarging magnification, and a second lens group. These constitutional elements of the catadioptric optical system are disposed such that light from the first surface passes through the first lens group, the beam splitter, the concave mirror, the beam splitter, and the second lens group in this order.

Abstract: A catadioptric reduction system operating in the deep ultraviolet range projects a reduced image of a mask on a substrate. A reducing optic made of a material transmissive to deep ultraviolet light has a concave front face covered by a partially reflective surface and a convex back face covered by a concave reflective surface surrounding a central aperture. The partially reflective surface transmits a portion of the light passing through the mask to the concave reflecting surface, which returns a portion of the transmitted light to the partially reflective surface. A portion of the returned light is reflected by the partially reflective surface on a converging path through said central aperture for producing a reduced image of the mask on the substrate.

Abstract: An optical system is provided for a FLIR mounted in a cylindrical turret ch has five folding mirrors, two doubling as scanning mirrors, numerous lenses with aspherical surfaces and different refractive indices, and a rotatable head mirror. Some of the lenses and mirrors being mounted on remote controlled electrically powered focusing or scanning means.

Abstract: A reflective scanning telescopic system comprises: a primary ellipsoidal mirror for collecting incoming light, a secondary hyperbolic mirror for reflecting the light collected by the primary mirror axially through the primary mirror, a tertiary ellipsoidal mirror, disposed behind the primary mirror for receiving the light from the secondary curved mirror, and a double bounce fold mirror for directing light reflected from the first fold mirror to the tertiary mirror and for reflecting light from the tertiary mirror past the first fold mirror to a light imaging system. Ideally, the telescopic system is mounted on a substantially rigid optical bench on a gimbal for supporting the optical bench and enabling the optical bench to scan in two dimensions by pivoting along roll and pitch axes.

Abstract: A system to transfer a pattern from a reticle to a substrate using a lens array having an arbitrarily wide image field that spans the width of the substrate. The disclosed system incorporates multiple, Wynne Dyson lenses arranged in serial pairs and staggered in position so that each dual serial Wynne Dyson lens system transfers a portion of the overall image from the reticle to the substrate as each are transported past the array of lens pairs. To transfer a complete, unbroken pattern on the substrate, each of the dual serial Wynne Dyson lens pairs are positioned in opposing and side-by-side positions and are staggered with respect to the scan direction. Each lens pair optionally includes individual internal adjustments, so that the pattern produced on the substrate does not contain any breaks or discontinuities.

Abstract: The invention is directed to a catadioptric reduction objective having a concave mirror, a beam splitter and several lens groups but without an additional lens group disposed between the concave mirror and the beam splitter. Catadioptric reduction objectives are disclosed having an image-side aperture of 0.52 and 0.58 for an imaging scale of 1:4 and are corrected for an unrestricted excimer laser for use in submicronlithography.

Abstract: An optical device for aligning an instrument so that active zones in the instrument are the same distance from the plane of a remote object comprising a lens attached to the instrument, the lens having a curved outer surface and a mirrored back surface. When the active zones in the instrument are aligned parallel to the plane of the remote object and the remote object is illuminated, the proper alignment is indicated by light emanating from the object being focused on a preselected spot.

Abstract: A catadioptric reduction projection optical system is of a construction in which an on-axis light beam is used in a catadioptric system, and is designed such that resolving power is not deteriorated and a stop can be disposed.

Abstract: A bar code reader system is adapted to read a micro-bar code and includes a light emitting body for irradiating a light beam onto a bar code surface on which the micro-bar code to be read is provided. A focusing lens focuses a reflected light from the bar code surface. An image pick-up device receives the focused reflected light and forms an image of the micro-bar code to be read. A cylindrical lens body is arranged to pass therethrough both the light beam from the light emitting body and the reflected light beam reflected from the bar code surface. The cylindrical lens body is oriented with an axis thereof substantially consistent with a bar code reading direction.

Abstract: This invention intends to provide a catadioptric reduction projection optical system of a construction in which an on-axis light beam is used in a catadioptric system and resolving power is prevented from being deteriorated, and more particularly a catadioptric reduction projection optical system having a first lens unit G1 of negative refractive power for diffusing a light beam from a reticle 1, a semi-transparent mirror 5 for transmitting therethrough the light beam from the first lens unit G1, plane parallel plates 2, 3 and 4 disposed obliquely with respect to the optical axis between the first lens unit G1 and the semi-transparent mirror 5 for correcting aberrations attributable to the semi-transparent mirror 5, a concave reflecting mirror 7 for returning the light beam emerging from the semi-transparent mirror 5 to the semi-transparent mirror 5 while converging the light beam, and a second lens unit G3 of positive refractive power for converging the light beam returned to the semi-transparent mirror 5 an

Abstract: In a cata-dioptric optical system having a combination of a reflection system and a refraction system for reduction-projecting an object on a first plane onto a second plane, a polarization beam splitter and a quarter wavelength plate are provided to split the incident light and the reflected light. The light beam directed to the polarization beam splitter is converted to a substantially collimated light beam by a first group of lenses. A second group of lenses are arranged between the polarization beam splitter and a concave reflection mirror to diverge the light beam. The light reflected by the concave reflection mirror is directed back to the polarization beam splitter with a substantially collimated state by the second group of lenses. The light beam from the second group of lenses transmitted through the polarization beam splitter is focused by a third group of lenses having a positive refraction power to form a reduced image.

Abstract: A broad band catadioptric optical reduction system using refractive elements made of different types of glass matched for color correction over a broad band width. A combination of fused silica and crown glass is used. An aspheric mirror is used for improved aberration correction. The optical system is adapted for use in lithography for semiconductor manufacturing in the I-line and is capable of 0.5 micron resolution at a wavelength of 365 nanometers.

Abstract: A real image mode optical system includes an objective lens forming an image of an object and an eyepiece for observing the image and is provided with a variable focal length mirror which dispenses with any polarizing plate so that a diopter change can be corrected due to the change of its optical power. Accordingly, the real image mode optical system has many advantages important for practical use that the reduction of the amount of light is slight, the characteristics are little changed by gravity, the number of parts is small with low manufacturing costs, the strain of the lens and the like of the optical system is not viewed, aberrations are little produced, and the effective aperture of the entire optical system can be set at a minimum.

Abstract: In a cata-dioptric optical system having a combination of a reflection system and a refraction system for reduction-projecting an object on a first plane onto a second plane, a polarization beam splitter and a quarter wavelength plate are provided to split the incident light and the reflected light. The light beam directed to the polarization beam splitter is converted to a substantially collimated light beam by a first group of lenses. A second group of lenses are arranged between the polarization beam splitter and a concave reflection mirror to diverge the light beam. The light reflected by the concave reflection mirror is directed back to the polarization beam splitter with a substantially collimated state by the second group of lenses. The light beam from the second group of lenses transmitted through the polarization beam splitter is focused by a third group of lenses having a positive refraction power to form a reduced image.