Approaching a Videoscope's Highest Physics-Limited Resolution to Improve RVI

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.