Abstract: A zoom lens forms an intermediate image at a position conjugate to a reduction side imaging plane and forms the intermediate image again on a magnification side imaging plane. The zoom lens includes a plurality of lens groups including at least two movable lens groups, which move by changing spacings between the groups adjacent to each other in a direction of an optical axis during zooming, at a position closer to the reduction side than the intermediate image. Among the plurality of lens groups, a final lens group closest to the reduction side has a positive refractive power, and remains stationary with respect to the reduction side imaging plane during zooming. The zoom lens satisfies predetermined conditional expressions (1) and (2) about the focal lengths of the movable lens groups.

Abstract: The present disclosure provides an optical imager and a method for imaging electromagnetic radiation. In one aspect, the optical imager includes an object array substantially located at an object plane, a first catadioptric element configured to substantially collimate, at a central plane, electromagnetic radiation emanating from the object array, a second catadioptric element configured to image the substantially collimated electromagnetic radiation from the central plane onto an image plane, and a detecting element substantially located at the image plane. The first catadioptric element includes at least one refractive surface and at least one reflective surface, and the second catadioptric element includes at least one refractive surface and at least one reflective surface.

Abstract: A projection lens system projects an image of a reduction side into a magnification side in an image projection device, a back glass being disposed on the reduction side. In the projection lens system, all of one or more negative lenses that satisfy, in a surface on the reduction side or a surface on the magnification side, condition |h/H|<2.0 defined by height h of a most off-axis principal ray and height H of an axial ray passing through a highest pupil position satisfy conditions Tn?98.5% and Dn/Db?0.05 defined by transmittance Tn, thickness Dn of the negative lens on an optical axis, and total thickness Db of the back glass.

Abstract: A telecentric optical apparatus that is capable of suppressing an increase in the number of components as well as achieving high precision optical axis alignment, is provided. The telecentric optical apparatus of the present invention is characterized in that it is provided with: a first telecentric lens surface that is provided on an object side; a second telecentric lens surface that is provided on an image side and that shares a focus position with the first telecentric lens surface; and an optical path trimming part that is provided, between the first telecentric lens surface and the second telecentric lens surface, in an outside region, which is located on a side further out than a light passing region having a center thereof located at the focus position, and that changes an optical path such that a light beam incident on the outside region is prevented from contributing to image formation.

Abstract: The present disclosure relates to the field of optical lenses and provides a camera optical lens. The camera optical lens includes, from an object side to an image side: a first lens; a second lens having a negative refractive power; a third lens having a positive refractive power; a fourth lens; a fifth lens; and a sixth lens. The camera optical lens satisfies following conditions: 1.50?f1/f?3.00; and 8.50?R9/d9?12.00. The camera optical lens can achieve a high imaging performance while obtaining a low TTL.

Abstract: Systems and methods in accordance with embodiments of the invention implement optical systems incorporating lens elements formed separately and subsequently bonded to low coefficient of thermal expansion substrates. Optical systems in accordance with various embodiments of the invention can be utilized in single aperture cameras, and multiple-aperture array cameras. In one embodiment, a robust optical system includes at least one carrier characterized by a low coefficient of thermal expansion to which at least a primary lens element formed from precision molded glass is bonded.

Abstract: Methods and apparatus are provided for optical coherence metrology or tomography across an extended area of an eye with improved registration. At least two optical coherence tomograms are acquired, with each tomogram containing data from regions of an anterior surface of the eye that are at least partially overlapping, and data from one or more deeper structures such as the retina or the anterior or posterior lens surfaces. The tomograms are then processed to register the data from the overlapping portions of the anterior surface regions, thereby registering the data from the deeper structures. In certain embodiments the reference arm of the apparatus comprises a compound reflector having at least two axially separated reflective surfaces for applying differential delays to different portions of the reference beam. The depth of field of the apparatus is thereby extended to enable measurement of eye length.

Abstract: A reflective imager design that is telecentric in image space, or equivalently telecentric at an image plane, or equivalently having an exit pupil located substantially at infinity, while also having an external entrance pupil and a high throughput or fast optical speed is described.

Abstract: A microscope imaging optical system has an entrance pupil on an object side and includes, in order from the object side, a first lens group including a biconvex lens and a negative lens having a concave surface on the object side, a second lens group including a negative lens having a concave surface on the object side, and a third lens group including a meniscus lens and a positive lens having a convex surface on an image side. The microscope imaging optical system satisfies conditional expressions 0.05<dp1/f<0.15 and 0.5<TT/f<0.9, where dp1 is the spacing between a lens, closest to the object, of the first lens group and the entrance pupil, f is the focal length of the microscope imaging optical system, and TT is the distance from the entrance pupil to the object image plane.

Abstract: An imaging system includes: an imaging apparatus that includes an image sensor and acquires a captured image; an optical system that includes a first objective and forms, within the image sensor, an optical image of a visual-field region that is a region within an object surface that corresponds to the objective field number (OFN) of the first objective; a motorized stage; and a control apparatus that constructs a first wide region image by piecing together a plurality of constituent images included in a plurality of captured images acquired by controlling the motorized stage and the imaging apparatus, the first wide region image being an image of a region wider than the visual-field region. Each of the plurality of constituent images is a portion of each of the plurality of captured images and is also at least a portion of each of images of a plurality of visual-field regions.

Abstract: The imaging optical system forms a first intermediate image at a position conjugate to the magnification side imaging surface and a second intermediate image at a position closer to a reduction side than the first intermediate image on an optical path and conjugate to the first intermediate image. The imaging optical system consists of a first optical system, a second optical system, and a third optical system in order from a magnification side to the reduction side along the optical path. The imaging optical system is configured to be telecentric on the reduction side. The imaging optical system satisfies predetermined conditional expressions.

Abstract: A microscope is described, having an illumination light path for illuminating a sample or object and a viewing light path for viewing the sample. The microscope includes an illumination light path focussing arrangement in the illumination light path, defining a substantially two-dimensional sample or object illumination region extending along an illumination direction of the illumination light path and transversely thereto. The microscope further includes an illumination region-confining device in the illumination light path for selectively illuminating a portion of the substantially two-dimensional object illumination region, wherein the portion of the substantially two-dimensional object illumination region is confined at least in the illumination direction and/or in the direction transversely thereto.

Abstract: The present invention discloses an ultra-small-sized 4K-resolution ultra-short-focus projection optical system, which is characterized by including in sequence in a projection direction: a DMD chip, an equivalent prism, a 4K oscillating mirror, a refraction lens assembly and an aspherical reflector. Through reasonable distribution of focal power, the semi-aperture size of the reflector is reduced to be less than 50 mm, and the assembling sensitivity is substantially reduced, so that batch production can be realized.

Abstract: A photographing optical lens system includes seven lens elements, the seven lens elements being, in order from an object side to an image side: a first lens element, a second lens element, a third lens element, a fourth lens element, a fifth lens element, a sixth lens element, and a seventh lens element. Each of the seven lens elements has an object-side surface facing toward the object side and an image-side surface facing toward the image side. At least one lens surface of the seven lens elements has at least one inflection point thereon.

Abstract: Microlithography projection objectives for imaging into an image plane a pattern arranged in an object plane are described with respect to suppressing false light in such projection objectives.

Abstract: An ultra-short throw projector device includes a lens system. The lens system includes a first lens group configured to form a first intermediate image from an incident display image; a second lens group configured to form a second intermediate image from the first intermediate image; an aperture configured to be disposed on a point where the first intermediate image is formed between the first lens group and the second lens group; a reflection mirror configured to reflect and magnify the second intermediate image and form an image on a screen; and a light path changing prism configured to change a light path in the vertical direction or other directions, the prism being disposed at a point on the light path of the lens system, at least one of an incident surface and a refracting surface being an aspherical surface or a freeform surface.

Abstract: A far infrared detector and objective lens and lens set thereof. The far infrared imaging lens set (10) comprises a first lens (100) and a second lens (200) arranged in sequence along a principal axis; the first lens (100) has a first curved surface (102) having a radius of curvature of 2.4×(1±5%) mm and a second curved surface (104) having a radius of curvature of 2×(1±5%) mm; the second lens (200) has a third curved surface (202) having a radius of curvature of 50×(1±5%) mm and a fourth curved surface (204) having a radius of curvature of 60×(1±5%) mm; wherein the first curved surface (102), the second curved surface (104), the third curved surface (202), and the fourth curved surface (204) are arranged in sequence; the first curved surface (102), the second curved surface (104) and the third curved surface (202) are all convex to the object side, and the fourth curved surface is convex to the image side. Distant targets can be detected in dark and foggy environments, and imaging capability is high.

Abstract: An optical lens comprising a first lens (L1), a second lens (L2), a third lens (L3), a fourth lens (L4), and a fifth lens (L5) that are sequentially arranged on a common optical axis in the transmission direction of an incident light. Both the first lens (L1) and the fifth lens (L5) are negative meniscus lenses. Both the second lens (L2) and the third lens (L3) are positive meniscus lenses. The fourth lens (L4) is a biconvex lens. The optical lens is applicable in an optical system of a laser processing apparatus. When an employed processing wavelength is different from a monitoring wavelength, imaging color differences in a monitoring system can thus be eliminated, specifically, when a wavelength in the infrared range is employed as a laser processing wavelength while a red wavelength serves as the monitoring wavelength, improved imaging effects are provided in the monitoring system, thus ensuring the quality of laser processing.

Abstract: Provided is an illumination optical apparatus for illuminating a mask with light from a light source. The apparatus includes an optical integrator configured to cause a light intensity distribution to be uniform in an emission end surface by reflecting the light incident from an incident end surface in an inner surface a plurality of times, an image forming optical system configured to form an image of the emission end surface of the optical integrator on the mask, and an adjustment unit configured to adjust telecentricity of the light so that a principal ray incident on the mask and a normal line of the mask approach parallelism and configured to be disposed outside the image forming optical system.

Abstract: Provided is an imaging lens assembly, including a first lens, a second lens, a third lens, a fourth lens and a fifth lens from an object side of the imaging lens assembly to an image side of the imaging lens assembly in turn. The first lens is of a positive focal power, an object side surface of the first lens is convex; the second lens is of a negative focal power, an image side surface of the second lens is concave; the third lens is of a focal power; the fourth lens is of a focal power; and the fifth lens is of a negative focal power; and a combined focal power of the third lens and the fourth lens is negative. The imaging lens assembly meets the following formulas: 2.0<f/ImgH<3.0; and 0<f1/f<0.5.

Abstract: Systems and methods for imaging a target are provided. A system includes a detector and a substantially bitelecentric lens assembly positioned between the detector and the target. A first optical assembly is configured to focus light received from the substantially bitelecentric lens assembly onto the detector. The substantially bitelecentric lens assembly and the first optical assembly are configured to produce a collimated light space between the substantially bitelecentric lens assembly and the first optical assembly. A second optical assembly is positioned within the collimated light space.

Abstract: A handheld, low-level laser apparatus includes a laser diode configured to generate a laser emission having an astigmatism. The apparatus further includes one or more corrective lens configured alone or in combination to correct the astigmatism and to collimate the laser emission, a divergence lens configured to diverge the laser emission after the laser emission passes through the one or more corrective lens, and a front lens configured to collimate the laser emission after the laser emission passes through the divergence lens. A low-level laser beam producing method includes repeatedly directing an IR laser emission through a series of lenses during a first set of time periods and repeatedly directing a visible laser emission through the series of lenses during a second set of time periods, each time period of the first set of time periods being distinct from each time period of the second set of time periods.

Abstract: Present embodiments provide for a mobile device and an optical imaging lens thereof. The optical imaging lens may comprise an aperture stop and five lens elements positioned sequentially from an object side to an image side. By controlling the convex or concave shape of the surfaces of the lens elements and designing parameters satisfying at least one inequality, the optical imaging lens may exhibit better optical characteristics and the total length of the optical imaging lens may be shortened.

Abstract: An apparatus is described for determining surface topography of a three-dimensional structure. The apparatus can include a probe and an illumination unit configured to output a plurality of light beams. In many embodiments, the apparatus includes a light focusing assembly. The light focusing assembly can receive and focus each of a plurality of light beams to a respective external focal point. The light focusing assembly can be configured to overlap the plurality of light beams within a focus changing assembly in order to move the external focal points along a direction of propagation of the light beams. The apparatus can include a detector having an array of sensing elements configured to measure a characteristic of each of a plurality of light beams returning from the illuminated spots and a processor coupled to the detector and configured to generate data representative of topography of the structure based on the measured characteristic.

Abstract: A wide angle lens is constituted by, in order from the object side to the image side: a front group having a negative refractive power; an aperture stop; and a rear group having a positive refractive power. The front group includes, in order from the object side to the image side, a first meniscus lens having a negative refractive power, and a second meniscus lens having a negative refractive power. The rear group includes a first cemented lens formed by cementing a negative lens and a positive lens, provided in this order from the object side, together, most toward the image side, and a lens having at least one aspherical surface and a negative refractive power provided adjacent to the first cemented lens at the object side thereof.

Abstract: A relay optical system exhibits an action of deflecting light with respect to passing luminous flux as a result of being provided with a light deflection member, and thus a cross-section of the luminous flux can be adjusted to a state of having an appropriate size (enlarged size), that is, a state in which an image is not completely formed but is blurred, at image formation positions of color modulation light valves. Therefore, it is possible to form a favorable image by minimizing moire.

Abstract: An imaging lens system includes: in order from an object side, a first lens including a negative meniscus lens having a convex surface facing the object side, a second lens including a positive lens having a convex surface facing the object side, a third lens including a negative lens having a concave surface facing an image side, a fourth lens including a positive lens having a convex surface facing the object side, and a fifth lens including a meniscus lens having a concave surface facing the image side, in which: the imaging lens system further includes an aperture stop arranged on the object side or the image side of the second lens, and the lens surface on the image side of the third lens and the lens surface on the object side of the fourth lens are bonded to each other.

Abstract: There is provided an endoscope objective optical system having a thin diameter, a wide in-water angle of view, a small variation in the angle of view, and a short overall length of the optical system. The endoscope objective optical system includes in order from an object side, a front group GF having a negative refractive power, an aperture stop, and a rear group GR having a positive refractive power, wherein the front group includes a first negative lens L1 and a second negative lens L2, and the following conditional expressions (1), (2), (3?), and (4) are satisfied: 1<Iw/ft<1.8??(1), 4<Lt/Iw<9.5??(2), 1.49?Lsf/ft?2.30??(3?), and 0.38<?La/Lsf<0.6??(4).

Abstract: An imaging optical system includes a first lens unit (B1) having a negative refractive power configured not to move for zooming from a wide-angle end to a telephoto end, and a plurality of lens units (B2 to B7) configured to move so that a space between lens units adjacent to each other changes during the zooming, the first lens unit includes a first lens subunit (B1a) having a negative refractive power, a second lens subunit (B1b) having a negative refractive power, and a third lens subunit (B1c) having a positive refractive power, the first lens subunit (B1a) is configured not to move for focusing from an infinity to a close range, and the second lens subunit (B1b) and the third lens subunit (B1c) constitute a focus moving unit configured to move, during the focusing, while a space between the second and third lens subunits is narrowed.

Abstract: A coordinate measuring machine has a workpiece support for holding a measurement object and a measuring head which can be displaced relative to the workpiece support. The measuring head carries an optical sensor. An evaluation and control unit is configured to determine spatial coordinates on the measurement object depending on a position of the measuring head relative to the workpiece support and depending on sensor data from the optical sensor. The optical sensor includes a lens assembly and a camera. The lens assembly comprises at least four separate lens-element groups. Three of these separate lens-element groups can be displaced along the optical axis of the lens assembly. A first lens-element group is arranged fixed in the region of the light-entry opening of the lens assembly. The coordinate measuring machine with the above-described lens assembly allows individual variation of magnification, focusing and resolution.

Abstract: An endoscope objective optical system comprises: a front group having a negative refractive power, a brightness diaphragm, and a back group having a positive refractive power in order from an object side, wherein the front group is composed of a first group, which is a first lens which is a single lens and a second group, which is a single lens or a cemented lens having a negative refractive power; 1<Iw/ft<1.8 0.6<Ia/Iw<0.95 |DL1/RL1a|<0.4 ?3<fL1/ft<?1 where Iw is a maximum image height in underwater observation, ft is a focal distance of an entire objective optical system in observation in the air, Ia is a maximum image height capable of transmitting a principal ray in the observation in the air, and DL1, RL1a, and fL1 are an outer diameter, a radius of curvature of an object side surface, and a focal distance, respectively of the first lens.

Abstract: An object of the present invention is to reduce the diameter, to make focus adjustment easy, and to achieve bright, wide-angle, high-resolution image quality. Provided is an endoscope objective optical system including, in this order from the object side, a front group having negative refractive power, an aperture stop, and a positive rear group. The front group includes, in this order from the object side, a first lens, which is a single lens having negative refractive power, and a second lens, which is a single lens having positive refractive power. The rear group includes a third lens, which is a single lens having positive refractive power, a cemented lens formed of a fourth lens having positive refractive power and a fifth lens having negative refractive power, and a sixth lens having positive refractive power.

Abstract: A zoom lens includes, in order from an object side to an image surface side, a first lens group having a positive refractive power, a second lens group having a negative refractive power, a third lens group having a negative refractive power, and a fourth lens group having a positive refractive power, the second lens group and the third lens group are moved such that the second lens group is located on a most object side at a wide-angle end and the third lens group is located on a most image surface side at a telephoto end during zooming.

Abstract: The invention relates to a telecentric modular zoom system for mapping an object plane on a sensor, in particular in a digital transmitted light microscope or incident light microscope having interchangeable lenses, comprising a fixed tube lens unit (LG1) and multiple optical assemblies (LG2, LG3, LG4, LG5, LG6), at least two of which are adjustably arranged relative to one another for the purpose of changing the magnification, characterized in that [sic]. According to the invention, a physical aperture (BL) conjugated relative to the rear focal points of the objectives used and having a variable diameter may be arranged in the beam path, wherein the rear focal points of the objective may be mapped in the space between a sensor image (BIE) and the intermediate image (ZB), the images of the rear focal points of the objectives (aperture BL) and the sensor image (BIE) do not lie within or migrate through the optical assemblies (LG2, LG3, LG4, LG5, LG6, LG7).

Abstract: The present disclosure provides an image capturing optical system comprising: a positive first lens element having a convex object-side surface; a negative second lens element having a concave object-side surface; a third lens element; a fourth lens element having a convex object-side surface and a concave image-side surface, the object-side surface and the image-side surface thereof being aspheric; a fifth lens element having a concave image-side surface concave, both of the object-side surface and the image-side surface being aspheric, at least one of the object-side surface and the image-side surface having at least one convex shape in an off-axis region thereof.

Abstract: A lens for projection substantially consists of a negative first lens with its concave surface facing a reduction side, a positive second lens with its concave surface facing the reduction side, a negative third lens with its concave surface facing a magnification side, a positive fourth lens with its convex surface facing the reduction side, a positive fifth lens and a positive sixth lens in this order from the magnification side. The reduction side is telecentric. The following conditional formulas (1) and (2) about refractive power P4 of a reduction-side surface of the second lens, refractive power P5 of a magnification-side surface of the third lens, and focal length f of an entire system are satisfied: ?3.0?1/(P4×f)??0.4??(1); and ?2.0?1/(P5×f)??0.2??(2).

Abstract: The present disclosure provides a telecentric optical assembly comprising a first portion of a telecentric optical link including a first kinematic mount having alignment structures, where the first kinematic mount can be attached to a first substrate having a first array of active optical elements; and a second portion of the telecentric optical link including a second kinematic mount having recesses configured to mate with the alignment structures, where the second kinematic mount can be attached to a second substrate having a second array of active optical elements. Additionally, the first and second kinematic mounts, when mated, can align optical beams between the first array of active optical elements and the second array of active optical elements.

Abstract: In an optical system for projection that is telecentric on a reduction side, a correction lens group substantially consisting of a part of lens groups in the optical system for projection is configured to move in the direction of an optical axis to correct a shift in a focal position caused by a change in temperature, and predetermined conditional formulas are satisfied.

Abstract: A variable magnification projection optical system substantially consisting of two lens groups of a first lens group having a positive refractive power and is moved during magnification change, and a second lens group having a positive refractive power and is moved during magnification change, in which the variable magnification projection optical system is configured such that the reduction side is telecentric.

Abstract: A variable-magnification projection optical system substantially consists of a negative first lens group that is disposed at the most enlargement-side position and is fixed during magnification change, a positive last lens group that is disposed at the most reduction-side position and is fixed during magnification change, and a plurality of lens groups that are disposed between the first lens group and last lens group and are moved during magnification change. The lens groups that are moved during magnification change substantially consist of three lens groups, wherein the most enlargement-side lens group is a negative lens group. Predetermined conditional expressions relating to a back focus of the entire system on the reduction side at the wide-angle end, a focal length of the entire system at the wide-angle end, a focal length of the last lens group, and a focal length of the first lens group are satisfied.

Abstract: A variable-magnification projection optical system substantially consists of a negative first lens group that is disposed at the most enlargement-side position and is fixed during magnification change, a positive last lens group that is disposed at the most reduction-side position and is fixed during magnification change, and a plurality of lens groups that are disposed between the first lens group and last lens group and are moved during magnification change. The most enlargement-side lens group (the second lens group) of the lens groups that are moved during magnification change has a negative refractive power. Predetermined conditional expressions relating to a back focus of the entire system on the reduction side at the wide-angle end, a focal length of the entire system at the wide-angle end, a focal length of the second lens group and a focal length of the last lens group are satisfied.

Abstract: The present disclosure provides a telecentric optical assembly comprising a first portion of a telecentric optical link including a first kinematic mount having alignment structures, where the first kinematic mount can be attached to a first substrate having a first array of active optical elements; and a second portion of the telecentric optical link including a second kinematic mount having recesses configured to mate with the alignment structures, where the second kinematic mount can be attached to a second substrate having a second array of active optical elements. Additionally, the first and second kinematic mounts, when mated, can align optical beams between the first array of active optical elements and the second array of active optical elements.

Abstract: In an optical system for projection that is telecentric on a reduction side, a correction lens group substantially consisting of a part of lens groups in the optical system for projection is configured to move in the direction of an optical axis to correct a shift in a focal position caused by a change in temperature, and predetermined conditional formulas are satisfied.

Abstract: The invention relates to a telecentric modular zoom system for mapping an object plane on a sensor, in particular in a digital transmitted light microscope or incident light microscope having interchangeable lenses, comprising a fixed tube lens unit (LG1) and multiple optical assemblies (LG2, LG3, LG4, LG5, LG6), at least two of which are adjustably arranged relative to one another for the purpose of changing the magnification, characterized in that [sic]. According to the invention, a physical aperture (BL) conjugated relative to the rear focal points of the objectives used and having a variable diameter may be arranged in the beam path, wherein the rear focal points of the objective may be mapped in the space between a sensor image (BIE) and the intermediate image (ZB), the images of the rear focal points of the objectives (aperture BL) and the sensor image (BIE) do not lie within or migrate through the optical assemblies (LG2, LG3, LG4, LG5, LG6, LG7).

Abstract: A compact, lens suitable for airborne photography and mapping has distortion less than 0.6% and is athermal from ?15° C. to +40° C. The lens is near-telecentric to less than 11°, apochromatic over the wavelength range 450 nm-650 nm, and has a full field of view of 60° (high quality field over 53°). The lens can be secondary color corrected. In embodiments, the focal length is 101 mm and the back working distance is more than 10 mm. Embodiments have a focal plane diameter of 104 mm and are compatible for use with a CMOS 1.8 gigapixel multiple FPA. In embodiments, the lens comprises three groups of optical elements, with an aperture located within the second optical group. In some embodiments the first group includes two elements, the second group includes six or seven elements, and the third group include three elements. In embodiments the lens (without window) is less than 180 mm long.

Abstract: A wide-angle lens comprising: an imaging lens system, including: a front lens group, an aperture, and a rear lens group, arranged in that order from an object side to an image side; wherein said front lens group comprises first and second lens elements, having negative power respectively, and a third lens that is a positive lens, arranged in that order from the object side to an aperture side; wherein said rear lens group comprises fourth and fifth lens elements, having positive power respectively, arranged in order from the aperture side to the image side; where an incident angle to an optical axis of the imaging lens system of a chief ray of a maximum angle of view passing through the aperture is ?I, the following Expression 1 is satisfied. 40° (degrees)<?I<60° (degrees)??Expression 1.

Abstract: A finder optical system includes, in the order from a display device side to an eye point side, a first lens group to increase a light beam height of a light beam bundle incident from a display device side and to emit the light beam bundle to the eye point side, and a second lens group having an image formation action.

Abstract: A variable-magnification projection optical system substantially consists of a negative first lens group that is disposed at the most enlargement-side position and is fixed during magnification change, a positive last lens group that is disposed at the most reduction-side position and is fixed during magnification change, and a plurality of lens groups that are disposed between the first lens group and last lens group and are moved during magnification change. The most enlargement-side lens group (the second lens group) of the lens groups that are moved during magnification change has a negative refractive power. Predetermined conditional expressions relating to a back focus of the entire system on the reduction side at the wide-angle end, a focal length of the entire system at the wide-angle end, a focal length of the second lens group and a focal length of the last lens group are satisfied.

Abstract: A variable magnification optical system for projection includes a first-lens-group having negative refractive power, and which is fixed when magnification of the system is changed, a second-lens-group having negative refractive power, and which is movable when magnification of the system is changed, a third-lens-group having positive refractive power, and which is movable when magnification of the system is changed, and a fourth-lens-group having positive refractive power, and which is fixed when magnification of the system is changed, which are arranged from the magnification side of the system in the order mentioned. The reduction side of the variable magnification optical system is telecentric, and formula 1.5<Bf/fw is satisfied, where Bf: back focus in air of entire system at wide angle end, and fw: focal length of entire system at wide angle end.

Abstract: In a projection optical system for use in an image projection apparatus illuminating an image display panel forming an image in accordance with a modulating signal with illumination light from a light source, the projection optical system includes first and second optical systems arranged along an optical path defining an upstream-downstream direction in the order described from upstream to downstream on the downstream side of the image display panel. The first optical system includes at least one dioptric system and has positive power. The second optical system includes at least one reflecting surface having power and has positive power. The image formed by the image display panel is formed as an intermediate image in the optical path, and the intermediate image is magnified and projected.