Optics
This section covers the values that are settled by calculation first: the size of one pixel on the object, working distance (WD) and depth of field. How many pixels a defect occupies on screen is decided by these numbers before any algorithm runs.
Start with these
- How to Calculate Machine-Vision Lens Focal Length — the basic formula from FOV, WD and sensor size
- Machine Vision Lens Calculator — where the shortcut formula breaks at higher magnification, plus depth of field and diffraction
- Vision Types Split First by Wavelength and Pixel Size — several vision methods compared in one table
- In SWIR, One Stop Down Erases a 3.4 µm Pixel — how diffraction covers a pixel as wavelength grows
Unfamiliar terms are explained in the Glossary, and a reading order across topics is in the Start Here guide.
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Reserve Room for Vision Cameras and Lighting at the Mechanical Design Stage
After mechanical design is done, there is no room for the light. A ring light for a 100 mm FOV needs a 106.5 mm opening at 30 mm, and a 40 mm low-angle…
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For Scratches on Highly Reflective Metal, Choose the Lighting First
Scratch lighting on polished or plated metal is chosen by surface shape: coaxial for flat mirrors with a 0.93° tolerance without a diffuser, a dome for curves, 15° low-angle light for hairlines, and…
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Changing the Sensor Means Recalculating the Illumination
A quantum efficiency of 15 % at 940 nm demands 4.9 times the photons and 2.85 times the watts of lighting compared with 550 nm, rising to 14.6 and 8.5 when the exposure…
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Why Are the Ends of a Line Scan Image Dark?
The ends of a line scan image sit at 0.77 of the center from cosine fourth falloff. A 1.3 gain fixes brightness but leaves SNR at 0.88, so shape the light 1.3 times…
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An 850 nm Band-Pass Filter Erases Factory Lights but Leaves Sunlight
An 850 nm band-pass filter erases factory LED light but keeps sunlight. What remains shrinks by the overdrive factor, not by the shorter exposure: a 40-level swing drops to 2 levels with the…
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A Mono Camera Catches PCB Color Differences When You Choose the Wavelength
With 625 nm light on a mono camera, 80 μm of copper exposed through a green mask images at 4.9 px, while the red channel of the color version of the same sensor…
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On Thick Parts, Silhouette Measurement Error Comes from the Backlight’s Angle
Gauge a 3 mm thick metal part on a diffuse backlight and the edge smears over 7.6 px; switch to collimated light with 0.29° divergence and it narrows to 1.5 px. In exchange,…
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Coaxial Light Alone Does Not Settle Fine Scratches on Polished Metal
Turn on collimated coaxial light over polished metal and only 31.8% of a 75 mm lens field lights up, while a 1° tilt shifts the bright circle 7.2 mm. Add a diffuser and…
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When Light Runs Short, a SPAD Sensor Counts Photons Instead of Extending Exposure
Split 100 photons over 30 frames and a standard CMOS sensor's signal-to-noise ratio falls from 7.5 to 4.5, while a SPAD adds them without read noise. But 256 pixels see only 4.27 mm,…
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In SWIR Imaging, Lighting and Aperture Keep the Defect Contrast
Film lifting in a film insert molded cover darkens by 7.7 % in SWIR transmission but only by 3 % for a 0.1 μm gap, and at 1,450 nm a 3.45 μm pixel…
