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I +81-3-3944-6210 Figure 2 2 θ EUROPE: JAPAN: | Divergent vs. Collimated Source Divergent Source Collimation Light rays scattering off the edges of an object Figure 2: Figure 1: Figure 3: f +1-856-547-3488 | +65 6273 6644

USA: ASIA: The rays of of hit the edges source The rays the divergent an object at many (see to light scattering which leads angles, different properties, based on the geometry material and light varies tered of part the such as smoothness and reflectivity, under inspection. originate to appear rays scattered the where effect an creates This of boundaries physical the within ofrays The partthe itself. col the reduces on, which dramatically hit the object straight source limated background the between edge well-defined a creates and scatter light and the silhouette. The smaller the divergence of the suited The smaller the divergence the better source, a light silhouetting illumination. is for light source with differently interact source light and a divergent a collimated how an object under inspection. ------(1) displays the displays , the diameter , the diameter θ ) shows the relationship the relationship shows Equation 1 Equation f D ( -1 Equation 1 Equation tan outlines a simple collimating set-up and | www.edmundoptics.com ® =

SILHOUETTING ILLUMINATION IN MACHINE VISION MACHINE IN ILLUMINATION SILHOUETTING θ Figure 1

EDMUND OPTICS

light collection. of the end diameter how demonstrates beam is equal the collimated that ofto the collimating lens used. does not factor in other aspects that may affect the quality of affect in other aspects that may does not factor a col of factor shape the as such beam, limated errors, or figure lens, the ofthe roughness surfaces. the refractive tradeoff and resultant divergence necessary that is often between limated the resultant beam is. beam is. the resultant limated beam in the collimated divergence left over between This equation length f. focal of collimating lens’s and the D, a source object. By positioning a divergent source at a positive lens’s focal focal lens’s at a positive source a divergent positioning object. By The size of refraction. undergoing after will collimate point, the rays well col lens used will determine and the specific how the source lel to one another. This is achieved by using optics to manipulate a manipulate using optics to by This is achieved one another. lel to away far sufficiently source placing a divergent beam or by divergent the the time is reaches by an object that it appears collimated from moves forward, the source is defined as a collimated light source, light source, is defined as a collimated the source forward, moves with the most common being a laser. ofparal light occurs when the rays Collimated propagate a source axis. A divergent light source is one whose illumination profile grows grows profile is one whose illumination light source A divergent axis. a standard like much its initial point, from away in size as it moves Ifflashlight. it in size as to grow appear does not source an optical viewing the divergence and numerical aperture (NA) of aperture and numerical (NA) viewing the divergence both optical of The divergence lenses is required. and imaging a source sources its optical to at with respect propagate is the angle that the light rays Divergence and Numerical Aperture and Numerical Divergence types ofthe different outlining Before re silhouetting illuminators, backlights, collimated backlights, and telecentric illuminators. Each illuminators. and telecentric backlights, collimated backlights, that, depend and disadvantages has distinct advantages illuminator be best integrated. ing on the application, may set-up will reduce scattering effects that may occur in other illumina that may effects scattering set-up will reduce and provide detection, edge accurate more for allow tion systems, that distinct illuminators four are There contrast. image overall better masked backlights, illumination: conventional silhouetted help create detail and the background ofdetail and the background using an illumination consider an image, in conjunction When used silhouetting illumination. called technique lighting a silhouetting lens, imaging quality telecentric with a high Machine vision applications requiring precise detection and mea detection precise applications requiring Machine vision ofsurement demand challenging il often and small defects edges an important between maximize the contrast To lumination set-ups. ILLUMINATION ® COPYRIGHT 2018 EDMUND OPTICS, INC. ALL RIGHTS RESERVED - has 0 10 Figure 6 90 +44 (0) 1904 788600 80

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L 0 6 | XE I P . 50 Fiber Optic Based Backlights 0 4 Figure 4: Edge Profile Obtained with Conventional Backlight Figure 5 Silhouette of Objective using Conventional Backlighting 30 Figure 6: +1-856-547-3488 | +65 6273 6644 Figure 5:

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| www.edmundoptics.com ® source lens SILHOUETTING ILLUMINATION IN MACHINE VISION IN MACHINE ILLUMINATION SILHOUETTING NA NA EDMUND OPTICS in microscopy applications or with objects which are non-reflective. non-reflective. are which with objects or applications microscopy in of their backlights are The additional advantages these conventional and smaller construction, wide availability price, lower comparably set-ups. space-constrained into integrate making them easy to optical fibers, behind a diffuser to create a light source for use in less a light source create to behind a diffuser optical fibers, com are These light sources setups. demanding silhouetting imaging is not necessary detection such as edge used when precise monly Conventional backlights are divergent light sources placed behind light sources divergent backlights are Conventional either constructed by often the object under inspection. They are oriented such as LEDs or randomly small light sources, placing many more critical. more Backlights Conventional silhouetting illumination would be beneficial, such as gauging the be beneficial, such as silhouetting illumination would lenses will often shape and size of on an object. Telecentric defects focal fixed standard to smaller numerical apertures compared have chosen even making the illumination thereby lenses, length imaging as the imaging lens. Due to their construction, the telecentric lens’s their construction, lens’s Due to the telecentric lens. as the imaging closer or farther moved remains constant as they are magnification applications where them ideal for the object. This makes from away scatter and stray light. When the NA of light. When the NA and stray than scatter larger a lens is much appear dim and lack sufficient contrast. may an image the source, used lens is often a telecentric In a silhouetting illumination set-up, ertures of as close to should be lens and source both the imaging Ifequal as possible. the numerical aperture of is much the source experience issues with one may than what the lens can handle, larger To maximize the efficiency numerical ap the system, To of an imaging ing the inverse ofing the inverse its F-number (as in resolution define the can also be used to the NA related, directly are and depth of field of lens. an imaging The numerical aperture of be included as part lens may an imaging of us also be estimated but it may the manufacturing specifications, that describes its ability to collect off-axis light. collect its abilitythat describes to ofthat the NA by its divergence, is defined source a Numerical apertureNumerical is one of most important the consider aspects to an im for pair a suitablewhen choosing source and illumination lens The numerical aperture of system. aging unit-less number a lens is a ® COPYRIGHT 2018 EDMUND OPTICS, INC. ALL RIGHTS RESERVED - 0 10 . 90 is an example of is an example +44 (0) 1904 788600

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L 0 6 | XE I P Collimated Backlight 50 Figure 11 Figure 9: 0 4 Edge Profile Obtained with Collimated Backlight Silhouette of Objective using Collimated Backlight 30 Figure 11: Figure 10: +1-856-547-3488 | +65 6273 6644

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.1 .2 .3 .4 .5 .6 .7 .8 .9 0 0 0 0 0 0 0 0 0 RELATIVE INTENSITY (ARB.) INTENSITY RELATIVE USA: ASIA: noticeable in silhouetting lighting setups. noticeable in silhouetting lighting setups. sharper with a edge. scatter profiled edge reduced ofThe appearance is confirmed a clean edge when looking at the of profile intensity the edge. about 20 dark, taking place over light to from slope in the transition the noise as in from and does not suffer pixels Collimated Backlights Collimated back collimated backlights, constructionSimilar in conventional to but a diffuser, and light sources divergent disparate lights contain ofreduce the divergence to collimating film an additional the have within a certain angular rays light allows only backlight. This film light source. profile low divergence, a lower exit, creating to range the benefit film provides without scatter This integrated low edge of the hassle of sized objects. different masking an existing backlight for is the improvement not trulyWhile these backlights are collimated, - - -

compares a backlight that compares Figure 8 | www.edmundoptics.com ® Edges of Objective using Conventional Backlight , the object under inspection is often much much is often , the object under inspection (Left) and Masked Backlighting (Right) Conventional Backlighting vs. Masked Backlighting SILHOUETTING ILLUMINATION IN MACHINE VISION IN MACHINE ILLUMINATION SILHOUETTING Figure 8: Figure 7: Figure 7 EDMUND OPTICS has been masked to one that has not. to has been masked that the mask will not eliminate the edge scatter completely, and the completely, scatter the edge that the mask will not eliminate sized objects. different for re-masked be continually need to light may in the lens field of as they move inspected Objects that are view also be masked. cannot effectively should be used to block offshould be used to portions of not the backlight that are because necessary the application. This method is advantageous for is to a light. The downside cost modification it is a quick and low In order to mask a backlight, an opaque material such as flock paper material mask a backlight, an opaque to In order

blocking these extraneous rays. blocking these extraneous the edges ofthe edges scattering edge and brighter the object and cause larger with the interacting edge near the be with just the rays than it would by can be reduced scattering the backlight, edge masking object. By As shown in As shown size ofsmaller than the overall that light the backlight. This means portions the unused from ofrays also be hitting the backlight may effect from the inherent divergence of divergence the inherent from remains prob effect the backlight lematic. creasing the distance between the backlight and object will make the object will make the backlight and between the distance creasing the always this is not However, appear less divergent. rays backlight’s light ifbecause solution best much too away far too is backlight the Iflost. be may scatter the object, the to close too is backlight the Masked Backlights Masked If of light at the edges scattered con a from obtained the silhouette in an application, backlight is unacceptable for divergent ventional, ® COPYRIGHT 2018 EDMUND OPTICS, INC. ALL RIGHTS RESERVED

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L 0 | 6 XE I P 50 0 4 Edge Profile Obtained with Telecentric Illuminator Edge Profile Obtained with Silhouette of Objective using a Telecentric Backlight Silhouette of Objective using a Telecentric 30 Figure 14: +1-856-547-3488 | +65 6273 6644 Figure 13:

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Achieving these high contrast silhouettes does have its disadvantag its have does silhouettes contrast high these Achieving larger higher in cost and much are illuminators telecentric Often es. Because of options. discussed backlighting than the previously the optical design of the size of lens, a telecentric element will the front determine the size of spot. If a is needed, the illuminated FOV a large size system increasing will be necessary, illuminator telecentric large of NA low the im an Additionally weight. and create helps source a difficult. alignment more but can make effects, scatter from free age If off and lens are illuminator the telecentric the alignment between will appear the illuminator by , the spot created a degree by even will be reduced. contrast dim and edge extremely out are when a lens and illuminator suffers the profile quickly how of alignment.

------confirms this back lit by a tel a by lit back Figure 14 Figure 10 Telecentric Illuminator Telecentric | www.edmundoptics.com ® Figure 12: SILHOUETTING ILLUMINATION IN MACHINE VISION IN MACHINE ILLUMINATION SILHOUETTING shows the same object from from object same the shows EDMUND OPTICS than 10 pixels. ecentric illuminator. The object exhibits none of ef scatter ecentric illuminator. the edge backlight and a sharper transi edge a conventional from seen fects backlight. the collimated to tion compared less dark occurringsharp light to over with the slope from transition, nation profile that creates sharp silhouettes and matches the NA of the sharp and matches that creates silhouettes nation profile than other backlighting methods. lens better imaging a telecentric Figure 13 typically within less than a degree of within less than a degree typically truetypes collimation. These of positioning precisely constructed are by illuminators telecentric an illumi creating LED, lens and a small powerful positive a large The main advantage of high degree is the advantage main The illuminator telecentric a of LED its optical design. Divergent through collimation achieved rays, collimated create that assemblies into integrated are sources

systems are used in conjunction they offer superior performance superior and used in conjunction they offer are systems backlight options. mentioned the previously to compared contrast source. A telecentric illuminator works similarly to a telecentric imag a telecentric to similarly works illuminator A telecentric source. of but instead ing lens, the aper optical elements projecting front the optical When these two a light source. it projects infinity, to stop ture Telecentric Illuminators Telecentric mea demand the most accurate applications When high precision as a light be considered should illuminator telecentric a surements, A collimated backlight is used where edge scatter is a concern, scatter but edge is used where backlight A collimated use of the do not allow restraints budget space and il a telecentric luminator. ® COPYRIGHT 2018 EDMUND OPTICS, INC. ALL RIGHTS RESERVED . - - - -

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L 0 | 6 Not truly collimated DISADVANTAGES Alignment Sensitive XE I Fair to Poor Uniformity P High NA leads to wasted light High NA Not a “one-size-fits-all”approach 50 High Divergence creates edge scattering Higher cost compared to conventional backlights 0 4 Inefficient when paired with low NA Telecentric lenses Inefficient when paired with low NA Similar disadvantages to conventional in un-masked portions 30 Collimated Backlighting (Green), and Telecentric Illumination Telecentric Collimated Backlighting (Green), and Combined Edge Profiles Obtained Using Conventional Backlighting (Blue), Combined Edge Profiles Obtained +1-856-547-3488 | +65 6273 6644

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.9 .8 .7 .6 .5 .4 .3 .2 .1 0 0 0 0 0 0 0 0 0 RELATIVE INTENSITY (ARB.) INTENSITY RELATIVE ofprofiles edge the shows against plotted object same the Figure 16: USA: ASIA: sized objects are under inspection. Collimated backlights are often often are backlights inspection. Collimated under are objects sized illumina telecentric to in cost and smaller in size compared lower Tel high precision. applications that require not satisfy but may tors, best uniformity and most the overall provide ecentric illuminators to their every set-up due not fit into but may detection, edge accurate size and higher cost. larger over about twice the amount ofover the conven The slope from pixels. backlight at to the collimated tional backlight has a similar profile ofby the high divergence induced first, but the additional scattering reach darker struggles that the profile to quickly the backlight shows backlight profile in the conventional The inconsistencies intensities. of on the edge lettering from are visible due to object that is only the another possible issue when highlighting scattering, the higher edge backlight. using a conventional the most importantKnowing aspects of ap your a lighting set-up for informed a more backlight choice help make plication will ultimately Conclusion Figure 16 the transition pixels many how one another as a comparison over The place. takes and the dark edge the bright background between cutoff, consistent most and quickest the has illuminator telecentric place slope that takes backlight has a consistent while the collimated - - - - Low Cost Low Profile High Uniformity High Uniformity ADVANTAGES East to Set-up and Align East to Set-up and Advantages and Disadvantages of Silhouetting Illumination Methods Larger sizes available in smaller package Lowers scatter vs Conventional Backlights Table 1: Table Smaller divergence to reduce edge scattering Easy & low cost Modification to existing backlight Lowest divergence creates highest contrast silhouettes Allows for a greater seperation of light source and object | www.edmundoptics.com ® SILHOUETTING ILLUMINATION IN MACHINE VISION IN MACHINE ILLUMINATION SILHOUETTING Masked Backlight Illuminated Spots Produced in Alignment (left) and 20 arcmin out of alignment (right) Illuminated Spots Produced in Alignment Collimated Backlight TYPE OF LIGHTING Telecentric Illuminator Telecentric Conventional Backlight Figure 15: EDMUND OPTICS backlights can help, but can be a time consuming process if process consuming time a be can but help, can backlights multiple backlights and the best choice will ultimately depend on your specific depend on your backlights and the best choice will ultimately backlight because use a standard to be tempting application. It may of unacceptable scat leads to but this often space and cost concerns, Masking the unused portions contrast. of poor edge and tering these Silhouetting illumination can be produced with different types of with different Silhouetting illumination can be produced mum diameter of diameter mum size of light beam, the physical the collimated the the These specifications provide numerical aperture. and the lens, lighting and lens combination. choosing an appropriate basis for the physical distance between the light and an object can be much much the light and an object can be distance between the physical a tel When considering distance. as a working than a stated larger the maxi the most applicable specifications are ecentric illuminator, focus properly. A telecentric illuminator does not focus light or create light or create does not focus illuminator A telecentric properly. focus not useful. Because of so this number is often an image, the efficient illuminator, telecentric light collection and collimation in a well-made The manufacturer’s specifications of may The manufacturer’s telecentric illuminator a is a mean distance value confusion. A working sometimes lead to as it lens, imaging telecentric ingful specification when used with a of distance (or range describes the physical distances) the lens can