OPTI-201/202 Geometrical and Instrumental Optics © Copyright 2018 John E. Greivenkamp 23-1 Section 23 Illumination Systems OPTI-201/202 Geometrical and Instrumental Optics © Copyright 2018 John E. Greivenkamp 23-2 z Image Optics Imaging formity, and the angular spread of light such as microscopes, slide projectors, ing system that also provides the illumination system that also provides ing for the optical system. Important for the ing the system about the object and ing the system about Object Optics Condenser Source considering the reflection. Opaque objects can be included by fold Opaque considerations are the amount of light, its uni as seen by the object. A projector is the general term for an imag include systems for the object. This would systems, copiers, comparators, etc. enlargers, photolithography The illumination system provides the light Illumination Systems OPTI-201/202 Geometrical and Instrumental Optics © Copyright 2018 John E. Greivenkamp 23-3 by the condenser optics into the EP of by the condenser spread is incident on the object. There is no the object. There spread is incident on fficient.also include This description could stem. This type of system is simple and ons of illumination systems is not standardized. standardized. not is illumination systems ons of ciency, specular illumination is used for most illumination ciency, specular is used is imaged directly onto the object. directly onto is imaged Source to Pupil Coupling Source No Source Coupling Source to Object Coupling Source • illumination – Critical source light the that the naming of these three classificati Note optical systems designed with an integral light source. with an optical systems designed provides uniform illumination, but it is light ine ambient or natural lighting conditions. There are three basic classifications of illumination systems: • illumination Specular – light the source is imaged light effi of its imaging optics. Because good attempt to image the source into imaging sy • illumination Diffuse – light with a large angular Illumination Classifications OPTI-201/202 Geometrical and Instrumental Optics © Copyright 2018 John E. Greivenkamp 23-4 z Image The projection lens diameter should The Image Source e the source is coupled into the EP of the er lens should be designed to as fast as on is the projection condenser system. A system. on projection condenser is the not universally used for this type of system. not universally used e transparent object, images the source into Lens bend source rays going through the edge of the Projection Object Transparent Lens Condenser often faster than f/1 on the source side). W Source be larger than the size of the source image. be larger The condenser lens serves as a field to condenser The object back into the projection lens. The condens into the projection lens. object back possible (f/# imaging system. Note that the term imaging system. Note specular is specific implementation. this actually refers to a although is sometimes used, term Koehler The The most common example of specular illuminati in close proximity to th lens, placed condenser pupil of the projection or imaging lens. Specular illumination Specular systems refer to wher Specular Illumination OPTI-201/202 Geometrical and Instrumental Optics © Copyright 2018 John E. Greivenkamp 23-5 Lens Rays Miss z .  is limited by the projection lens.  Lens Projection rectly between the source and the projection ection of the transparency, and non-uniform and ection of the transparency, llected and used is defined by the solid ould project only the center of image. ould Object ze of the projection lens  Source The amount of the source energy that is co The amount of the source energy angle given by the angular si Without a condenser lens, the light collection angle lens, a condenser Without Each point on the source illuminates only a s illumination can result. Only object points di small source w A lens will be projected. Need for the Condenser Lens for the Condenser Need OPTI-201/202 Geometrical and Instrumental Optics © Copyright 2018 John E. Greivenkamp 23-6 z Image Source ze (or the object size). A greater A ze (or the object size). Lens Projection tire source. As a result, very uniform tire source. size or geometry. There is no requirement There is no size or geometry. ll the light collected by the condenser passes ll the light collected by condenser ource illuminates all the object, and points on Object '  Lens ' is limited lens si by the condenser Condenser  Source Uniformity and Light Efficiency Uniformity and With a condenser lens, each point on the s a condenser With each point on the object is illuminated point on by the en each illumination can result regardless of the source the source size to project entire object. on The collection angle A is collected. fraction of the source energy the projection lens. through OPTI-201/202 Geometrical and Instrumental Optics © Copyright 2018 John E. Greivenkamp 23-7 z z z Object Object Object is limited by the angular size of source. Lens Diffuser ent –to be large. appears source the Condenser   Source Source Source With a diffuser – a diffuser With are pres all angles With a bare source, the apparent source size the apparent a bare source, With – a condenser With same apparent angular source size results. the This defines the angular range of the illumination This defines the angular range at the object. Apparent Source Size OPTI-201/202 Geometrical and Instrumental Optics © Copyright 2018 John E. Greivenkamp 23-8 z Image/Screen Image Source a condenser lens f/# (usually as fast a condenser be well corrected as its is only to purpose than the source image size. This determines image size. than the source ect-image distances are determined by the by the object size and any needed separation Lens (magnification and object-image distance). (magnification and Projection Object Transparent Lens Condenser Source The projection lens diameter must be larger projection lens diameter must be larger The screen position and size and the object size •lens diameter is determined condenser The the object. Pick lens and the condenser between The condenser focal length can then possible). be found. •image in the projection lens. position places the source source The • the f/# of projection lens. not lens need aberrations of the condenser The into the aperture of projection lens. image the source •the obj projection lens focal length and The Projection Condenser Design Projection Condenser OPTI-201/202 Geometrical and Instrumental Optics © Copyright 2018 John E. Greivenkamp 23-9 z Image Image Source form of illumination in optical systems ed to be two coupled optical The systems. the chief ray of imaging system, and into the pupil of the lens, the source is into the pupil of lens, source the marginal ray of the imaging system. the marginal Lens can be thought of as a field lens. Projection Object Transparent Lens Condenser Source conjugate to the pupil, and the condenser to the pupil, and conjugate The projection condenser system can be consider system becomes ray of the condenser marginal system becomes chief ray of the condenser Specular illumination is the most commonly used with integral sources. Since the condenser lens images the source Since the condenser Coupled Optical Systems OPTI-201/202 Geometrical and Instrumental Optics © Copyright 2018 John E. Greivenkamp 23-10 z Objective Object changes the color or temperature of changes ws the overall light level to be varied by nt applied to the source. With tungsten illumination in microscopes to often used used, and the field diaphragm changes the Substage Diaphragm Substage Condenser Lens Condenser Field Diaphragm Source provide control of the illumination. An intermediate source image is produced. The control of the illumination. intermediate provide An source image is produced. substage diaphragm (at the source image) allo that is of the source the amount changing amount of the object that is illuminated. Koehler illumination is a type of specular Koehler Illumination Using the substageUsing the illumination the source size and level is to change condenser the voltage or curre preferable to changing filaments, changing the voltage or current also filaments, changing the light. OPTI-201/202 Geometrical and Instrumental Optics © Copyright 2018 John E. Greivenkamp 23-11 z Image Lens Projection rectly onto the object. While very light Source Images ore also appears as a brightness modulation ore also appears ed. The source brightness distribution is required; an example is a tungsten ribbon Object type of system is typically small. type Lens Condenser Source filament. The field of view of this field of view filament. The efficient, critical us illumination is rarely superimposed directly on the object and theref is very uniform source of the image. A Critical illumination images the light source di source light the Critical illumination images Critical Illumination OPTI-201/202 Geometrical and Instrumental Optics © Copyright 2018 John E. Greivenkamp 23-12 z Image rtion of a diffuser into the system. Very diffuser into the rtion of a opal glass. Other materials such as white systems tend to be very light inefficient. systems tend to be Lens ciency and degree of diffuseness on ciency depends and degree of diffuseness so used. The diffuser is The diffuser transilluminatedso used. and Projection the source resulting in greater uniformity of Object Diffuser Source illumination. glass or are commonly made of ground Diffusers drafting film or translucent plastic are al and The light effi placed behind the transparency. the material choice. The diffuser increases the apparent size of diffuser The uniform illumination but these can be achieved, Diffuse illumination is usually achieved by the inse Diffuse Illumination OPTI-201/202 Geometrical and Instrumental Optics © Copyright 2018 John E. Greivenkamp 23-13 ure. Different grinding grit sizes can be grinding the surface of a glass plate. be more efficient and less be more efficient uniform than has been flashed with a thin milky-white The light distribution depends on the details on light distribution depends The the thickness of opal coating, multiple The light distribution from opal glass can be glass can light distribution from opal The peaked in the forward direction. Ground glass direction. Ground in the forward peaked of the light is directed backwards. by dispersing crystallites such as fluorine focusing screens in cameras. Surface diffusers, such as ground glass, tend to such as ground Surface diffusers, such as opal glass or translucent plastic volume diffusers, sheets. compounds into the volume of coating. compounds The surface becomes a random “prismatic” struct glass. coarse or fine ground to produce used of the grind, and this distribution is often or as viewing is also used surface one glass is a plate where Opal coating. The white color is produced of close to uniform or Lambertian. Because scattering can occur and a large fraction Ground glass diffusers are formed roughening or glass diffusers are formed roughening Ground Ground Glass Ground and Opal Glass OPTI-201/202 Geometrical and Instrumental Optics © Copyright 2018 John E. Greivenkamp 23-14 Out Lens Imaging Ray Scattered If specular or narrow angle or narrow If specular the used, illumination is scratch will scatter the light out of the optical system, the scratch will appear and dark in the image. In Ray Scattered Ray Lens Imaging Scattered on the object, such as a scratch or defect in the object, such on object is not hidden even by diffuse object illumination. is not hidden even by diffuse ansparency becomes part of the object and will part of the object and ansparency becomes Transparency Diffuser present with diffuse illumination provides Transparency Angle Narrow scratch suppression that will hide phase errors phase that will hide scratch suppression the substrate of object transparency. This greater range of illumination angles Scratch Suppression With diffuse illumination, many diffuse With input angles are present, different and while some rays are scattered the scratch, out of the system by other rays will scattered into the be The aperture of the imaging lens. visibility of the scratch in image is significantly decreased. A scratch or defect in the transmission of the A For example, a scratch in the emulsion of tr For example, in the image. be seen Illumination OPTI-201/202 Geometrical and Instrumental Optics © Copyright 2018 John E. Greivenkamp 23-15 An integrating bar or light pipe provides or light pipe integrating bar An diffuse light with a significant increase in bar has simple diffusers. The efficiency over a rectangular cross section with polished surfaces. The source is placed at one end of the bar, and TIR occurs at each face. The at that the transparency tunnel diagram shows the other end of bar sees a rectangular (2D) array of source images. The effect is of greater range similar A to a kaleidoscope. illumination angles or diffuseness results. The bar geometry and the TIR critical angle images. With six limit of source the number polished faces, integrating bars are expensive. Diffusers can also be placed over the input and/or output ends of the bar to further mirror increase the diffuseness. Hollow instead of solid glass. be used tunnels can Integrating Bars Source Source Images Images Source OPTI-201/202 Geometrical and Instrumental Optics © Copyright 2018 John E. Greivenkamp 23-16 as the angle of incidence decreases with the source images appear on a sphere, and there increase or decrease the size of source relative In this case, to the transparency. is some loss of TIR for the outside images multiple bounces. The number of source images is reduced. The integrating bar can also be tapered to Tapered Integrating Bars OPTI-201/202 Geometrical and Instrumental Optics © Copyright 2018 John E. Greivenkamp 23-17 Exit Port Port Entrance Source The ultimate in diffuse illumination is provided illumination is diffuse ultimate in The by an integrating sphere. The inside of a hollow sphere is coated with a highly-reflective diffuse white coating. Light directed into the entry port undergoes many random reflections before escaping through the exit port. The output light that is a brightness is extremely uniform with independent of viewing angle. It is a very good This approximation to a Lambertian source. system is also extremely light inefficient. The two ports are usually at 90° to prevent the direct viewing of the source and first source in also used are reflection. Integrating spheres replacing precision measurement radiometers by with a detector. the source Integrating Sphere OPTI-201/202 Geometrical and Instrumental Optics © Copyright 2018 John E. Greivenkamp 23-18 z increase the light level in projection t to the source. An improvement of less An t to the source. stem is redirected back into the system. stem is redirected back ource at the center of curvature mirror. Condenser Image Source Source R Mirror Concave system. The classic solution is to place the s system. The sy of the out originally heading Light that was The source image is placed on top of or adjacen is obtained. than a factor of two Placing a concave mirror Placing a concave behind the source can Concave Source Mirrors OPTI-201/202 Geometrical and Instrumental Optics © Copyright 2018 John E. Greivenkamp 23-19 z ondenser lens. In addition, a concave cold lens. In addition, a concave ondenser e heat or infrared IR radiation to exit out Condenser projectors. Heat absorbing glass or a hot projectors. Heat absorbing the heat management in the optical system. the heat management he cold) and transmits he cold) and the IR light. hot) and transmits hot) and the visible light. Heat Absorbing Glass or Hot Mirror Heat Source Concave Cold Mirror Heat Management A cooling fan is often required to supplement cooling A A cold mirror reflects the visible light (t A Heat management is a significant issue for most mirror the source and c can be placed between mirror the source to allow th can be added behind of the system. the back hot mirror reflects the IR light (the A OPTI-201/202 Geometrical and Instrumental Optics © Copyright 2018 John E. Greivenkamp 23-20 z Lens Image Source Projection finity. The designs of systems of this type CONDENSER f bolic mirror (at its the solid focal point), and r by placing the source at the focus of by the condenser by a factor of ten or more. by the condenser by s not influence the light collection efficiency. condenser. The mirror shape is usually sr. The amount of light intercepted and reflected by the of light intercepted and reflected by The amount sr. Transparency  Condenser HA Glass Source MIRROR f The direct light from the source imaged by the condenser lens. direct light the condenser The from the source imaged by with the reflected light. source image produced The Mirror Parabolic concave mirror. The source image occurs at in source image occurs mirror. The concave almost ignore the forward light through the lens doe f/# of the condenser parabolic. The Dramatic increases in illumination level occu Parabolic Reflectors The source can be located deep inside the para angle of the mirror can be more than 2 the light directly collected exceed mirror can images are formed: two source mirror, a parabolic concave With OPTI-201/202 Geometrical and Instrumental Optics © Copyright 2018 John E. Greivenkamp 23-21 Source Source Images be segmented into small To provide a greater level of diffuseness, the a greater level of diffuseness, provide To can surface of the parabola each behind is formed virtual source A flat mirrors. source images are located in a plane These facet. details The of the vertex of reflector. behind the faceted parabolic reflector are complicated, but it for design purposes can be modeled as an source located at or near the concave extended mirror. mirror The aperture defines the extent of The condenser lens images extended source. the The aperture into the pupil of projection lens. match this image. projection lens aperture should With the smooth reflector, there is little diffuseness, there will non-uniformity in the illumination and be of the light in the reflected bulb to the shadow due light. Faceted Reflectors OPTI-201/202 Geometrical and Instrumental Optics © Copyright 2018 John E. Greivenkamp 23-22 de of the light bulb. of the light from center reflector. of the reflector can deviate from a parabola. gned so that uniform illumination so is achieved gned forward through the aperture defined by its coming out of the si Bulb Light Source Images The light from each source image is directed facet. In addition, the light bulb will block some facet. In addition, the light bulb will block size and tilt of the facets are desi The number, overall “shape” The at the object transparency. The design of the reflector utilizes the light Faceted Reflector Design OPTI-201/202 Geometrical and Instrumental Optics © Copyright 2018 John E. Greivenkamp 23-23 z Lens Images Projection Reflected flector. The total view is limited by the flector. aperture is imaged into the projection lens. Because of the difference in sold angles Because the direct image contains much less light. ews the individual source images through the the individual source images through ews Condenser with Slide Source Faceted Reflector of the reflector versus the condenser lens, of the reflector versus the condenser A direct image of the source is also formed. direct image of the source A The transparency or condenser system The transparency or condenser vi the re the respective facets on formed by windows This overall overall aperture of the reflector. System with the Facet Reflector Source Images OPTI-201/202 Geometrical and Instrumental Optics © Copyright 2018 John E. Greivenkamp 23-24 z Source R  = 110°: R  Reflector Parabolic . The amount of light is determined by the Source Images greatly exceeds the collection by the condenser the collection by greatly exceeds r r s s Half Angle z 00  30° .842 Condenser 110° 8.43 C CC  RR 

2(1cos)       0 0    Source   Parabolic Reflector: The source is inside the parabola. Assume The source is inside the parabola. Parabolic Reflector: Condenser or Classic System: Assume an f/1 collection angle: Assume or Classic System: Condenser lens in the classic projection condenser system lens in the classic projection condenser the source. optics as seen by of the collection or condenser solid angle The light collection of a parabolic reflector Light Collection Efficiency The exact gain is difficult as filament bulb to estimate factors such geometry and exact gain is difficult due The shadowing. OPTI-201/202 Geometrical and Instrumental Optics © Copyright 2018 John E. Greivenkamp 23-25 Parts of the filament Parts of the are when partially obscured viewed from different locations on the object. coil of a tungsten wire. larger light bulb is not always an option an always is not larger light bulb ith a little For example, diffusion added. may shadow other parts of the filament. may shadow This tly etched or a weak ground glass added. In at there is never enough light!!). The system light!!). The enough at there is never specular first and then add diffusers. E 3D structure. It is often a structure. It is often 3D Filamant Illumination (A major rule of optical engineering is th should be designed as specular illumination w lens might be ligh side of the condenser one these systems, be sure to design them as The filament in a light bulb is a of this structure, the filament itself Because can result filament in non-uniform illumination. shadowing In many applications the image quality of diffuse illumination In many is required, but the of specular illumination A throughput is needed. Illumination Issues OPTI-201/202 Geometrical and Instrumental Optics © Copyright 2018 John E. Greivenkamp 23-26 e source into a small aperture. The source is image is formed at the other focus. An image is formed at the other focus. Source Reflector Smooth Elliptical placed at one focus of the ellipse, and a real fiber optic bundle. light into a is coupling example An elliptical reflector can be used to focus th Elliptical Reflectors OPTI-201/202 Geometrical and Instrumental Optics © Copyright 2018 John E. Greivenkamp 23-27 Side View View Top behind the presenter. In addition to bending behind collapsed into radial zones. An image is An into radial zones. collapsed on from the projection screen introduces a Fresnel Condenser Platen To Screen To Fold Mirror Source To determine parity, the diffuse reflecti the diffuse determine parity, To other reflection. like any parity change the light path, the fold mirror creates the proper image parity for the audience. the light path, fold mirror creates the proper lens is impractical condenser a conventional of the large size transparency, Because thick lens is The a Fresnel lens is used. and by each zone, and these images add incoherently, so that produced the diffraction-based resolution is that of a single zone. The overhead projector uses projection condenser illumination projector uses projection condenser to project a large overhead The transparency onto a projection screen located Overhead Projector OPTI-201/202 Geometrical and Instrumental Optics © Copyright 2018 John E. Greivenkamp 23-28 z Image Stop Central f y features or defects on an object. In a y features or defects on ect is inserted, any feature or imperfection ect is inserted, any ) some light past the obscuration. These e of the source as well final image. que disk or a knife edge. With no object disk or a knife edge. que Imaging Lens que are aerodynamic flow visualization and Object Scattered Rays Collimator Source inspecting glass for inhomogeneity and stria. and inspecting glass for inhomogeneity Some applications of the schlieren techni schlieren light system, from a small is collimated the source before passing through imaging lens forms an imag An object plane. The image of the source is by an opa blocked the obj black. When present, the image appears the object will scatter on (or refract or diffract bright in the image. the object will appear localized areas on Narrow angle illumination Narrow can be used to identif Schlieren Systems OPTI-201/202 Geometrical and Instrumental Optics © Copyright 2018 John E. Greivenkamp 23-29 Gary Settles, University of Pennsylvania Gary Settles, Schlieren Images Schlieren is a German term meaning “streak” OPTI-201/202 Geometrical and Instrumental Optics © Copyright 2018 John E. Greivenkamp 23-30 Side Point Illumination Scattering Objective Surface ng directional light is lighting. The source the orientation of features, or surface bright in the image. This technique is ection Setups for transmission microscopy. ed knife edge (schlieren) or by directional tion within the FOV of the objective misses tion within the FOV . Features or imperfections the surface . on in a ring around the lens. If object is in a ring around Ring Point Source Scattering Objective Surface derivatives, can be measured using an orient field). illumination (dark With both dark field and schlieren techniques, field and dark both With placed to the side of objective lens, or perfectly smooth (a mirror), a specular reflec the image is dark the objective aperture, and appear objective and will scatter light into the especially common in machine vision and refl dark field measurements also exist. Dark field illumination is another technique usi field illumination technique is another Dark Dark Field Illumination OPTI-201/202 Geometrical and Instrumental Optics © Copyright 2018 John E. Greivenkamp 23-31 Tissue Paper Fibers -Tissue Wikipedia Grain Boundaries - www.cartech.com www.ma-tek.com Bright Field and Dark Field Images OPTI-201/202 Geometrical and Instrumental Optics © Copyright 2018 John E. Greivenkamp 23-32

Photon Engineering they hit something. At the surface, ount as well as a lens element. The input ional model of the system. Rays are stem in optical order according to the stem in optical order according surfaces in any order and number of refraction occurs. It is used to design, It is used refraction occurs. flected and/or scattered according to defined scattered according flected and/or e “daughter” rays each propagate until another prescription. At each surface, reflection or mirrors. lenses and tolerance systems of optimize and use a three-dimens Non-Sequential Raytracing from launched a source and they propagate until ray can be partially transmitted, partially re surface properties. The can be a lens m ray is split into a number of rays, and thes ray can encounter A surface is encountered. times. Sequential Raytracing traces rays through a sy traces rays through Sequential Raytracing Non-Sequential Raytracing OPTI-201/202 Geometrical and Instrumental Optics © Copyright 2018 John E. Greivenkamp

Photon Engineering 23-33 ajectories of rays as they interact with Reflector and Integrating Bar Reflector and trained by a predetermined order of surfaces. - Projectors - and architectural Automotive - Backlighting - design Illumination -scattered light analysis or Stray - Ghost images/Lens flare - modeling Source Weightings can be applied to Weightings of light for the percentage account associated with each resulting ray. the optical system. The rays are not cons Important applications of non-sequential raytracing include: Non-Sequential Raytracing follows the physical tr Non-Sequential Raytracing OPTI-201/202 Geometrical and Instrumental Optics © Copyright 2018 John E. Greivenkamp 23-34 Photon Engineering Example – Reflector Automotive OPTI-201/202 Geometrical and Instrumental Optics © Copyright 2018 John E. Greivenkamp 23-35 Optical Research Associates Optical Research Roadscene with Headlights and LED Streetlights Scene Simulation OPTI-201/202 Geometrical and Instrumental Optics © Copyright 2018 John E. Greivenkamp 23-36 Optical Research Associates Optical Research Example –Projector LCD OPTI-201/202 Geometrical and Instrumental Optics © Copyright 2018 John E. Greivenkamp 23-37 Addition of a baffle at Addition of a baffle the primary mirror. Addition of a second baffle. pplications/lens/straylight.html http://www.integra.jp/en/specter/a Catadioptric Lens System –Catadioptric Lens Baffles Light and Stray Scattering from edges of lenses and mounts OPTI-201/202 Geometrical and Instrumental Optics © Copyright 2018 John E. Greivenkamp

www.lightworkdesign.com 23-38 Because these images are out of focus, they Because ff an even number of surfaces, so that there are fracting surfaces in the optical system. effects of scattered light and ghost images. images. ghost scattered light and of effects red light, ghost images are unintended images images are unintended red light, ghost , then  = 1%, the relative irradiance  where N is the number of reflections. where N caused by specular Fresnel reflections from re To form a ghost image, the light must reflect o etc. four reflection ghosts, two-reflection ghosts, of the iris as shape diaphragm. often appear Unlike the degradation of images from scatte Ghost Images and Lens Flare Ghosts are usually only formed by bright formed by are usually only Ghosts sources within or just outside the field of If the surface reflectivity is view. relative irradiance of an will have the ghost  For example, a two reflection a two ghost from For example, uncoated glass will have an irradiance 0.16% of the direct image about AR coated the ghost. For source producing glass with will be 0.01%. In addition to overall will be 0.01%. transmission, the minimization of ghosts is coatings AR reason for high quality a good on camera lenses. Lens flare is the term applied to the combined the to term applied flare is the Lens