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Approaching a Videoscope’s Highest
Physics-Limited Resolution to Improve RVIWhat goes into optimizing inspection resolution to increase probability of detection?
Frank Lafleur
Long Beach, CA — October 25th, 2016
Premise of RVI
Acquire an image that is not possible to see with the human eye on its own.
Need to see as much of the area in front of the remote viewing device as
possible and have the entire view in focus and with ideal light and color.
Better technology alone does not achieve these two key factors, but design and
assembly skill maximize physics.
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Main Components of a Remote Video Image
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Physics & skill Technology
Physics Challenges Acting Against Achieving a Good RVI Image
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Diameter
Flexibility
& access
requirements
Portability
Durability
The Physics of Maximizing Resolution
In reference to optics
– Aberrations and distortions
In reference to aperture
– Light
– Diffraction
– Circle of confusion
In reference to camera chip
– Size of chip
– Size of pixels
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Optics — Monochromatic Optical Aberrations
Spherical aberration
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Optics — Monochromatic Optical Aberrations
Astigmatism
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Optics — Monochromatic Optical Aberrations
Distortion
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Optics — Monochromatic Optical Aberrations
Modulation transfer function (MTF) and line pair capability
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Optics — Chromatic Optical Aberrations
Chromatic aberrations: axial and lateral
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Aperture — Effects of Aperture on Image
Light availability and dispersion
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Aperture — Effects of Aperture on Image
Diffraction and airy disc
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Aperture — Effects of Aperture on Image
Depth of field and circle of confusion
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Chip — Physics Considerations of Camera Chip
Size of chip
– It must typically fit inside a 4 mm or 6 mm distal end. If that isn’t a limitation,
the CCD size and aperture size are also not limited.
Size of pixels
– Pixel sizes from 1.9 µm to 5.6 µm are common. At this size, the precision of
the required optic system is critical. Based on this, as pixel sizes approach
2.0 µm, diffraction patterns must be kept to 4–5 µm or they risk being
diffraction limited.
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Common Corrective Measures
Lens materials
– The ability to use multiple materials to make a lens system opens many
possibilities.
– This type of system costs more and is more complex, including durability
considerations.
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Common Corrective Measures
Stopping aperture
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Makes it darker; not
good for inspections.
Common Corrective Measures
Offset aperture
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Longer distal end;
often not acceptable for
navigation/inspections.
Common Corrective Measures
Lens systems
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Best solution, but costly
and requires greater
assembly skill.
Where are physics causing bottlenecks?
Micro-optics manufacturing
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Greater chip density makes even the
smallest aberrations more obvious.
Where are physics causing bottlenecks?
Diffraction limitation and aperture requirements
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Higher density chip will not correct
for diffraction limitation.
Conclusion and Advice
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• Be aware of the major physics factors:
• Micro manufacturing and assembly
• Diffraction limitation for <=6 mm videoscopes
• Don’t be lead astray by inconsequential specifications that don’t translate to
image quality:
• Pixel count, lumens, pixel size
• Use MTF and line pairs as guides, but color reproduction can only really
be evaluated in person.
• See videoscopes for yourself, on your application.