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`Articles
`Application Notes | Articles | EO Tech Tools | FAQ and Glossary | Marketing Literature | Video Resources
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`Sort by: Date
`06/2009 - "Telecentric Illumination for Vision-System Backlighting" by Bruce Butkus - Machine Design
`04/2009 - "Optical Fabrication: Advances in sputtering benefit coating costs" by Iain Macmillan - Laser Focus World
`04/2009 - "A Vision System for the E-Pedigree Era" by Gregory Hollows and David Pfleger - Pharmaceutical
`Manufacturing
`03/2009 - "Optical Advances Speed Rapid Prototyping" by Amr Khalil - Design World
`03/2009 - "Matching Lenses and Sensors" by Gregory Hollows and Stuart Singer - Vision Systems Design
`03/2009 - "Putting More Meaning in Imaging" by Mike May - Bioscience Technology
`03/2009 - "Souping up optics with design and simulation software" - BioOptics World
`02/2009 - "Optical coatings industry: the picture looks bright" by Caren Les - Photonics Spectra
`02/2009 - "Special Report: The Largest Market in the World" by Barry Hochfelder - Advanced Imaging
`12/2008 - "Edmund Optics Doubles Precision-Asphere Production Capacity" by John Wallace - Laser Focus World
`11/2008 - "Sleeping with the Dragon: The yin and yang of doing business with China" by Robert Edmund - Laser Focus
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`11/2008 - "Manufacturing high-quality aspheres – conventional or in a hybrid process" by Jeremy Govier and Martin
`Weinacht - Photonik
`11/2008 - "Precision Prism Manufacturing Art or Science?" by Andrew Lynch - Nasa Tech Briefs
`10/2008 - "Glasses roll aspheres into the mainstream" by Gregg Fales - Optics & Laser Europe
`09/2008 - "Getting inside optical filters" by Mike May - BioOptics World
`09/2008 - "Into the UV" by Andrew Wilson - Vision Systems Design
`08/2008 - "Tracking fluid flow with two channels" by Hank Hogan - BioPhotonics
`07/2008 - "Optics optimizes fluorescence" by Kristin Vogt - BioOptics World
`07/2008 - "Innovate or Die" by Kathy Sheehan - SPIE (Copyright 2008, SPIE Professional Magazine. Used with
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`Phone: 1-800-363-1992 or 1-856-573-6250, Fax: 1-856-573-6295
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`Home > Matching Lenses and Sensors
`Matching Lenses and Sensors
`March 1, 2009
`
`Social Media Tools
`
`With pixel sizes of CCD and CMOS image sensors becoming smaller, system
`integrators must pay careful attention to their choice of optics
`
`Share
`
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`
`Greg Hollows and Stuart Singer
`Each year, sensor manufacturers fabricate sensors with smaller pixel sizes. About 15
`years ago, it was common to find sensors with pixels as small as 13 µm. It is now
`common to find sensors with standard 5-µm pixel sizes. Recently, sensor
`manufacturers have produced pixel sizes of 1.4 µm without considering lens
`performance limits. It is also common to find sensors that contain 5 Mpixels and
`individual pixel sizes of 3.45 µm. In the next generation of image sensors, some manufacturers expect to produce devices
`with pixel sizes as small as 1.75 µm.
`
`Sponsored by:
`
`Click here to enlarge image
`
`In developing these imagers, sensor manufacturers have failed to communicate with lens manufacturers. This has resulted in
`a mismatch between the advertised sensor resolution and the resolution that is attainable from a sensor/lens combination. To
`address the problem, lens manufacturers now need to produce lenses that employ higher optical performance, lower f-
`numbers (f/#s), and significantly tightened manufacturing tolerances so that these lenses can take advantage of new
`sensors.
`Understanding light
`To understand how lenses can limit the performance of an imaging system, it is necessary to grasp the physics behind such
`factors as diffraction, lens aperture, focal length, and the wavelength of light. One of the most important parameters of a lens
`is its diffraction limit (DL). Even a perfect lens not limited by design will be diffraction limited and this figure, given in line
`pairs/mm, will determine the maximum resolving power of the lens. To calculate this diffraction limit figure, a simple formula
`that relates the f/# of the lens and the wavelength of light can be used.
`
`DL = 1/[(f/#)(wavelength in millimeters)]
`
`After the diffraction limit is reached, the lens can no longer resolve greater frequencies. One of the variables affecting the
`diffraction limit is the speed of the lens or f/#. This is directly related to the size of the lens aperture and the focal length of the
`lens as follows:
`
`f/# = focal length/lens aperture
`
`APPL-1025 / Page 2 of 15
`APPLE INC. v. COREPHOTONICS LTD.
`
`

`

`http://www.vision-systems.com/articles/print/volume-14/issue-3/features/matching-lenses-and-sensors.html
`The diffraction pattern resulting from a uniformly illuminated circular aperture has a bright region in the center, known as the
`Airy disk, which together with the series of concentric bright rings around it is called the Airy pattern. The diameter of this
`18 captures
`pattern is related to the wavelength of the illuminating light and the size of the circular aperture.
`10 Aug 2012 - 27 Dec 2017
`
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`
`JUL AUG APR
`
`10
`2011 2012 2016
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`
`FIGURE 1. The Airy disk is the
`smallest point on which a beam
`of light can be focused (top).
`The center bright spot contains
`approximately 84% of the total
`spot image energy, 91% within
`the outside diameter of the first
`ring, and 94% of the energy
`within the outside diameter of
`the second ring. The 3-D light
`intensity of the Airy disk shows
`how the light is distributed
`(bottom).
`Click here to enlarge image
`
`This is important since the Airy disk is the smallest point a beam of light can be focused. The disk comprises rings of light
`decreasing in intensity and appears similar to the rings on a bulls-eye target. The center bright spot contains approximately
`84% of the total spot image energy, 91% within the outside diameter of the first ring and 94% of the energy within the outside
`diameter of the second ring and so on (see Fig. 1a and 1b). The Airy disk diameter (ADD) can be calculated by
`
`ADD = (2.44)(f/#)(wavelength)
`
`The image spot size can be considered the diameter of the Airy disk, which comprises all its rings. The spot size that a lens
`produces has an increasingly significant role in digital imaging. This is because the individual pixel size on the latest sensors
`has been reduced to the point where it is comparable or smaller than the Airy disk size.
`
`It is important to consider the Airy disk diameter at a particular f/# since the Airy disk diameter can be considerably larger
`than the individual pixel size. Using a lens set to f/8.0 will be performance limited by an individual pixel size <12.35 µm (see
`Table 1). In the table, all the values are given using a 632.8-nm wavelength.
`
`APPL-1025 / Page 3 of 15
`APPLE INC. v. COREPHOTONICS LTD.
`
`

`

`http://www.vision-systems.com/articles/print/volume-14/issue-3/features/matching-lenses-and-sensors.html
`
`18 captures
`10 Aug 2012 - 27 Dec 2017
`
`Go
`
`JUL AUG APR
`
`10
`2011 2012 2016
`
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`
`
`f 🐦
`▾ About this capture
`
`Click here to enlarge image
`
`null
`Sensor resolution
`While the diffraction limit in line pairs/mm determines the resolving power of the lens, the resolution limit of the image sensor,
`commonly referred to as the Nyquist frequency (NF), is also expressed in terms of line pairs/mm where
`
`NF = 1/[(pixel size)(2)]
`
`Table 2 shows the Nyquist frequency limits for pixel sizes now available in machine-vision cameras. What is required is a
`lens system with a fairly low f/# to even theoretically achieve the sensor limited resolution. It is common practice for such
`lenses to be calibrated with f/#s relating to infinity.
`
`Click here to enlarge image
`
`As an object is viewed at a finite distance in most machine-vision systems, these f/#s are no longer valid. A new “finite” f/#
`value must be calculated and employed on all system calculations such as spot size and resolution limits. A simple way to
`calculate the “finite” f/# (ff/#) is
`
`APPL-1025 / Page 4 of 15
`APPLE INC. v. COREPHOTONICS LTD.
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`

`Go
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`
`ff/# = (infinity f/#)(magnification+1)
`http://www.vision-systems.com/articles/print/volume-14/issue-3/features/matching-lenses-and-sensors.html
`
`18 captures
`Using the above equation, and assuming a unity optical magnification of 1, the ff/# for the lens is twice the infinity f/# value.
`10 Aug 2012 - 27 Dec 2017
`Thus, as a rule of thumb, a lens listed with an f/# of 1.4 can be estimated to have an f/# of 2.8 when used in a machine-vision
`systems. Smaller and smaller pixel sizes force lenses to run at very low f/#s to theoretically achieve the resolutions limits of
`the sensor.
`
`As the f/# gets lower and lower, it become more difficult to design and manufacture lenses that approach the theoretical limit.
`While some lens designs can approach theoretical limits, once manufacturing tolerances, different wavelength ranges,
`sensor alignment, microlenses, different lens mounts, and the desire to use these lenses over a range of working distances
`are taken into account, it becomes nearly impossible to approach the limits.
`Lens design
`When designing lenses, optical engineers take into account many different factors to achieve the desired resolution. In any
`lens design, whether for a web camera or for a high-resolution imaging system, the lens performance varies with the working
`distance, ff/#, or the wavelength range.
`
`Each lens has a sweet spot where the best performance is obtained. As factors such as working distance are varied, system
`performance fall-off will occur. The higher the resolution of the system, the faster this will happen.
`
`In the case of Sony’s 5-Mpixel sensor that features 3.45-µm pixels, for example, sensor-limited resolution really cannot be
`achieved even theoretically both at very short working distances and at longer working distances with the same lens. Thus, it
`is critical to discuss with lens manufacturers what the working distance for a specific application will be and to understand
`how the lens will perform at that distance.
`
`Any lens product cannot be used to make such systems work effectively. Remember: A lens is not guaranteed to perform in
`a 5-Mpixel camera simply because it is specified as a 5-Mpixel lens.
`
`In the past, machine-vision systems used lenses developed for microscopy, photography, and security applications. While
`these lenses can be very good, they do not maximize the capabilities of imagers used in machine vision. Additionally, the
`high level of price pressures in these markets requires loosened manufacturing tolerances and such lenses may omit the
`features of those specifically designed for machine vision.
`Tighter tolerances
`The tighter the tolerance of the manufacturing process, the more closely the lens will achieve the parameters of an ideal
`design. Tighter manufacturing tolerances also lead to a more repeatable lens—important when installing multiple systems—
`and better image quality across the entire sensor. Because image quality generally falls off at the corner of the image first,
`loosening tolerances only enhances and in many cases accelerates these effects.
`
`System developers do not require a background in optical mechanical design to determine if lens tolerances are tight
`enough. However, it should be determined whether the design information is for the ideal/nominal design or for the tolerance
`design. Since many lenses are specified using tolerance design information, the lens vendor may need to provide test
`images set for a specific application requirement.
`
`The higher the resolution of the system, the lower the f/#needs to be to resolve spots small enough to match the camera’s
`resolution. The lower the f/# of the lens, the larger the cone of light for a specific distance that the lens is working in, and the
`faster rays will diverge before and after best focus. If the alignment of the lens to the sensor is not tight enough, even a lens
`that meets specific resolution requirements may not yield a system that meets specification.
`
`Figure 2 shows a sensor (in red) tipped in relation to the lens system where the dashes represent individual pixels. The solid
`red line (right) indicates the point at which the defocusing of the cones of light produced by the lens grows larger than the
`pixels, creating out-of-focus imaging beyond those points. If enough pixels are added and the alignment is not perfect, the
`system will become defocused.
`
`FIGURE 2. A sensor (red) may be tipped in relation to the lens system.
`
`APPL-1025 / Page 5 of 15
`APPLE INC. v. COREPHOTONICS LTD.
`
`

`

`Red dashes represent individual pixels; solid red line indicates the point at
`http://www.vision-systems.com/articles/print/volume-14/issue-3/features/matching-lenses-and-sensors.html
`which the defocusing of the cones of light produced by the lens grows
`larger than the pixels, creating out-of-focus imaging beyond those points. If
`18 captures
`enough pixels are added and the alignment is not perfect, the system will
`10 Aug 2012 - 27 Dec 2017
`become defocused.
`
`Click here to enlarge image
`
`Go
`
`JUL AUG APR
`
`10
`2011 2012 2016
`
`👤 ⍰ ❎
`
`
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`▾ About this capture
`
`Asking a camera manufacturer how they guarantee the alignment of their sensor with relation to the camera lens mount is
`the best way to reduce the risks associated with this issue. Higher levels of alignment do add cost, but performance is
`maximized. For high levels of pixel density in linescan and 11-Mpixel and 16-Mpixel cameras, alignment tools may be
`designed into the lens or camera.
`Increasing fill factor
`Microlenses increase the fill factor of the sensor by capturing as much light as possible. However, like any lenses they have
`an acceptance angle at which they will still effectively collect light and focus it onto the active portion of the pixel (see Fig. 3).
`If the external lens used to form an image on sensors that use microlenses exceeds this angle, then the light does not reach
`the sensor (see Fig. 4).
`
`FIGURE 3. Microlenses increase the fill factor of the sensor by capturing
`as much light as possible. However, they have an acceptance angle at
`which they will effectively collect light and focus it onto the active portion of
`the pixel.
`
`Click here to enlarge image
`
`As sensors grow larger and larger, the acceptance angles of each of these microlenses do not change. The angle of light
`from the center of the external lens to the pixels farther and farther from the center of the sensor does change, as can be
`seen by the green and red ray traces of Fig. 4.
`
`FIGURE 4. If the external lens
`used in a design exceeds the
`acceptance angle of the
`microlens used with the
`sensor, light from objects
`farther from the center field of
`view of the lens (green and
`red) may not reach the
`sensor.
`Click here to enlarge image
`
`As sensor resolutions increase, light must still reach individual microlenses on the sensor at angles as low as 7° so that
`shading or roll-off does not occur. To overcome this, lens manufacturers such as Schneider Optics and Edmund Optics will
`be offering external lenses that are near telecentric in image space. In such designs, the angle of light farther and farther
`from the center will remain on-axis and no angular roll-off will occur (see Fig. 5).
`
`APPL-1025 / Page 6 of 15
`APPLE INC. v. COREPHOTONICS LTD.
`
`

`

`http://www.vision-systems.com/articles/print/volume-14/issue-3/features/matching-lenses-and-sensors.html
`
`18 captures
`10 Aug 2012 - 27 Dec 2017
`
`Go
`
`JUL AUG APR
`
`10
`2011 2012 2016
`
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`
`
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`▾ About this capture
`
`FIGURE 5. To overcome
`the problem associated with
`microlens-based sensors,
`lens manufacturers will offer
`external lenses that are
`near telecentric in image
`space. The angle from light
`farther and farther from the
`center will remain on-axis
`and no angular roll-off will
`occur.
`Click here to enlarge image
`
`Many have enjoyed the advances in sensor development associated with consumer cameras, but products designed for
`consumer applications and those for machine vision are vastly different. There will always be overlap and commonality
`between these areas, but understanding machine-vision optics is mandatory for those building high-resolution imaging
`systems.
`
`Greg Hollows is director, machine vision solutions, at Edmund Optics, Barrington, NJ, USA; www.edmundoptics.com; and
`Stuart Singer is vice president of Schneider Optics, Hauppauge, NY, USA; www.schneideroptics.com.
`
`Share
`
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`APPL-1025 / Page 7 of 15
`APPLE INC. v. COREPHOTONICS LTD.
`
`

`

`Matching Lenses and Sensors
`
`Close
`
`With pixel sizes of CCD and CMOS image sensors becoming smaller, system integrators must pay careful
`attention to their choice of optics
`Greg Hollows and Stuart Singer
`Each year, sensor manufacturers fabricate sensors with smaller pixel sizes. About 15 years ago, it was
`common to find sensors with pixels as small as 13 µm. It is now common to find sensors with standard 5-
`µm pixel sizes. Recently, sensor manufacturers have produced pixel sizes of 1.4 µm without considering
`lens performance limits. It is also common to find sensors that contain 5 Mpixels and individual pixel sizes
`of 3.45 µm. In the next generation of image sensors, some manufacturers expect to produce devices with
`pixel sizes as small as 1.75 µm.
`
`Click here to enlarge image
`
`In developing these imagers, sensor manufacturers have failed to communicate with lens manufacturers.
`This has resulted in a mismatch between the advertised sensor resolution and the resolution that is
`attainable from a sensor/lens combination. To address the problem, lens manufacturers now need to
`produce lenses that employ higher optical performance, lower f-numbers (f/#s), and significantly tightened
`manufacturing tolerances so that these lenses can take advantage of new sensors.
`Understanding light
`
`APPL-1025 / Page 8 of 15
`APPLE INC. v. COREPHOTONICS LTD.
`
`

`

`To understand how lenses can limit the performance of an imaging system, it is necessary to grasp the
`physics behind such factors as diffraction, lens aperture, focal length, and the wavelength of light. One of
`the most important parameters of a lens is its diffraction limit (DL). Even a perfect lens not limited by
`design will be diffraction limited and this figure, given in line pairs/mm, will determine the maximum
`resolving power of the lens. To calculate this diffraction limit figure, a simple formula that relates the f/# of
`the lens and the wavelength of light can be used.
`DL = 1/[(f/#)(wavelength in millimeters)]
`After the diffraction limit is reached, the lens can no longer resolve greater frequencies. One of the
`variables affecting the diffraction limit is the speed of the lens or f/#. This is directly related to the size of
`the lens aperture and the focal length of the lens as follows:
`f/# = focal length/lens aperture
`The diffraction pattern resulting from a uniformly illuminated circular aperture has a bright region in the
`center, known as the Airy disk, which together with the series of concentric bright rings around it is called
`the Airy pattern. The diameter of this pattern is related to the wavelength of the illuminating light and the
`size of the circular aperture.
`
`FIGURE 1. The Airy disk is the smallest
`point on which a beam of light can be
`focused (top). The center bright spot
`contains approximately 84% of the total
`spot image energy, 91% within the
`outside diameter of the first ring, and
`94% of the energy within the outside
`diameter of the second ring. The 3-D
`light intensity of the Airy disk shows how
`the light is distributed (bottom).
`Click here to enlarge
`image
`
`This is important since the Airy disk is the smallest point a beam of light can be focused. The disk
`comprises rings of light decreasing in intensity and appears similar to the rings on a bulls-eye target. The
`center bright spot contains approximately 84% of the total spot image energy, 91% within the outside
`diameter of the first ring and 94% of the energy within the outside diameter of the second ring and so on
`(see Fig. 1a and 1b). The Airy disk diameter (ADD) can be calculated by
`
`APPL-1025 / Page 9 of 15
`APPLE INC. v. COREPHOTONICS LTD.
`
`

`

`ADD = (2.44)(f/#)(wavelength)
`The image spot size can be considered the diameter of the Airy disk, which comprises all its rings. The spot
`size that a lens produces has an increasingly significant role in digital imaging. This is because the
`individual pixel size on the latest sensors has been reduced to the point where it is comparable or smaller
`than the Airy disk size.
`It is important to consider the Airy disk diameter at a particular f/# since the Airy disk diameter can be
`considerably larger than the individual pixel size. Using a lens set to f/8.0 will be performance limited by an
`individual pixel size <12.35 µm (see Table 1). In the table, all the values are given using a 632.8-nm
`wavelength.
`
`Click here to enlarge image
`
`null
`Sensor resolution
`While the diffraction limit in line pairs/mm determines the resolving power of the lens, the resolution limit
`of the image sensor, commonly referred to as the Nyquist frequency (NF), is also expressed in terms of line
`pairs/mm where
`
`NF = 1/[(pixel size)(2)]
`Table 2 shows the Nyquist frequency limits for pixel sizes now available in machine-vision cameras. What
`
`APPL-1025 / Page 10 of 15
`APPLE INC. v. COREPHOTONICS LTD.
`
`

`

`is required is a lens system with a fairly low f/# to even theoretically achieve the sensor limited resolution.
`It is common practice for such lenses to be calibrated with f/#s relating to infinity.
`
`Click here to enlarge image
`
`As an object is viewed at a finite distance in most machine-vision systems, these f/#s are no longer valid. A
`new “finite” f/# value must be calculated and employed on all system calculations such as spot size and
`resolution limits. A simple way to calculate the “finite” f/# (ff/#) is
`ff/# = (infinity f/#)(magnification+1)
`Using the above equation, and assuming a unity optical magnification of 1, the ff/# for the lens is twice the
`infinity f/# value. Thus, as a rule of thumb, a lens listed with an f/# of 1.4 can be estimated to have an f/#
`of 2.8 when used in a machine-vision systems. Smaller and smaller pixel sizes force lenses to run at very
`low f/#s to theoretically achieve the resolutions limits of the sensor.
`As the f/# gets lower and lower, it become more difficult to design and manufacture lenses that approach
`the theoretical limit. While some lens designs can approach theoretical limits, once manufacturing
`tolerances, different wavelength ranges, sensor alignment, microlenses, different lens mounts, and the desire
`to use these lenses over a range of working distances are taken into account, it becomes nearly impossible
`to approach the limits.
`Lens design
`When designing lenses, optical engineers take into account many different factors to achieve the desired
`resolution. In any lens design, whether for a web camera or for a high-resolution imaging system, the lens
`performance varies with the working distance, ff/#, or the wavelength range.
`
`APPL-1025 / Page 11 of 15
`APPLE INC. v. COREPHOTONICS LTD.
`
`

`

`Each lens has a sweet spot where the best performance is obtained. As factors such as working distance are
`varied, system performance fall-off will occur. The higher the resolution of the system, the faster this will
`happen.
`In the case of Sony’s 5-Mpixel sensor that features 3.45-µm pixels, for example, sensor-limited resolution
`really cannot be achieved even theoretically both at very short working distances and at longer working
`distances with the same lens. Thus, it is critical to discuss with lens manufacturers what the working
`distance for a specific application will be and to understand how the lens will perform at that distance.
`Any lens product cannot be used to make such systems work effectively. Remember: A lens is not
`guaranteed to perform in a 5-Mpixel camera simply because it is specified as a 5-Mpixel lens.
`In the past, machine-vision systems used lenses developed for microscopy, photography, and security
`applications. While these lenses can be very good, they do not maximize the capabilities of imagers used in
`machine vision. Additionally, the high level of price pressures in these markets requires loosened
`manufacturing tolerances and such lenses may omit the features of those specifically designed for machine
`vision.
`Tighter tolerances
`The tighter the tolerance of the manufacturing process, the more closely the lens will achieve the parameters
`of an ideal design. Tighter manufacturing tolerances also lead to a more repeatable lens—important when
`installing multiple systems—and better image quality across the entire sensor. Because image quality
`generally falls off at the corner of the image first, loosening tolerances only enhances and in many cases
`accelerates these effects.
`System developers do not require a background in optical mechanical design to determine if lens tolerances
`are tight enough. However, it should be determined whether the design information is for the ideal/nominal
`design or for the tolerance design. Since many lenses are specified using tolerance design information, the
`lens vendor may need to provide test images set for a specific application requirement.
`The higher the resolution of the system, the lower the f/#needs to be to resolve spots small enough to match
`the camera’s resolution. The lower the f/# of the lens, the larger the cone of light for a specific distance that
`the lens is working in, and the faster rays will diverge before and after best focus. If the alignment of the
`lens to the sensor is not tight enough, even a lens that meets specific resolution requirements may not yield
`a system that meets specification.
`Figure 2 shows a sensor (in red) tipped in relation to the lens system where the dashes represent individual
`pixels. The solid red line (right) indicates the point at which the defocusing of the cones of light produced
`by the lens grows larger than the pixels, creating out-of-focus imaging beyond those points. If enough
`pixels are added and the alignment is not perfect, the system will become defocused.
`
`APPL-1025 / Page 12 of 15
`APPLE INC. v. COREPHOTONICS LTD.
`
`

`

`FIGURE 2. A sensor (red) may be tipped in relation to the lens system. Red dashes represent
`individual pixels; solid red line indicates the point at which the defocusing of the cones of light
`produced by the lens grows larger than the pixels, creating out-of-focus imaging beyond those
`points. If enough pixels are added and the alignment is not perfect, the system will become
`defocused.
`Click here to enlarge image
`
`Asking a camera manufacturer how they guarantee the alignment of their sensor with relation to the camera
`lens mount is the best way to reduce the risks associated with this issue. Higher levels of alignment do add
`cost, but performance is maximized. For high levels of pixel density in linescan and 11-Mpixel and 16-
`Mpixel cameras, alignment tools may be designed into the lens or camera.
`Increasing fill factor
`Microlenses increase the fill factor of the sensor by capturing as much light as possible. However, like any
`lenses they have an acceptance angle at which they will still effectively collect light and focus it onto the
`active portion of the pixel (see Fig. 3). If the external lens used to form an image on sensors that use
`microlenses exceeds this angle, then the light does not reach the sensor (see Fig. 4).
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`FIGURE 3. Microlenses increase the fill factor of the sensor by capturing as much light as
`possible. However, they have an acceptance angle at which they will effectively collect light and
`focus it onto the active portion of the pixel.
`Click here to enlarge image
`
`As sensors grow larger and larger, the acceptance angles of each of these microlenses do not change. The
`angle of light from the center of the external lens to the pixels farther and farther from the center of the
`sensor does change, as can be seen by the green and red ray traces of Fig. 4.
`
`FIGURE 4. If the external lens used
`in a design exceeds the acceptance
`angle of the microlens used with the
`sensor, light from objects farther from
`the center field of view of the lens
`(green and red) may not reach the
`
`sensor.Click here to enlarge
`image
`
`As sensor resolutions increase, light must still reach individual microlenses on the sensor at angles as low
`as 7° so that shading or roll-off does not occur. To overcome this, lens manufacturers such as Schneider
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`Optics and Edmund Optics will be offering external lenses that are near telecentric in image space. In such
`designs, the angle of light farther and farther from the center will remain on-axis and no angular roll-off
`will occur (see Fig. 5).
`
`FIGURE 5. To overcome the
`problem associated with microlens-
`based sensors, lens manufacturers
`will offer external lenses that are
`near telecentric in image space.
`The angle from light farther and
`farther from the center will remain
`on-axis and no angular roll-off will
`
`occur.Click here to enlarge
`image
`
`Many have enjoyed the advances in sensor development associated with consumer cameras, but products
`designed for consumer applications and those for machine vision are vastly different. There will always be
`overlap and commonality between these areas, but understanding machine-vision optics is mandatory for
`those building high-resolution imaging systems.
`Greg Hollows is director, machine vision solutions, at Edmund Optics, Barrington, NJ, USA;
`www.edmundoptics.com; and Stuart Singer is vice president of Schneider Optics, Hauppauge, NY, USA;
`www.schneideroptics.com.
`
`To access this Article, go to:
`http://www.optoiq.com/optoiq-2/en-us/index/display/oiq-articles-tool-template.articles.vision-
`systems-design.volume-14.issue-3.features.matching-lenses-and-sensors.html
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