マシンビジョン向けイメージセンサーの選定：用途に応じた解像度、シャッター方式、およびレンズの組み合わせ

Global Shutter vs Rolling Shutter for Machine Vision

Global shutter starts and ends integration for every pixel together, giving all rows one common exposure interval; the capture is not instantaneous, and motion blur still scales with exposure time. Rolling shutter exposes rows sequentially over a readout period lasting microseconds to milliseconds. For a stationary scene, the difference is invisible. For anything that moves relative to the camera (the object, the camera, or both), rolling shutter introduces geometric distortion because the scene changed between when the first row and the last row were sampled.

Strobed illumination needs care on rolling shutter. If the strobe fires while only part of the array is integrating, only those rows record the flash, leaving a bright band. Under strobe-dominated illumination with negligible ambient, the pulse width sets effective exposure and motion blur; otherwise the programmed exposure accumulates ambient smear too. The exposure setting only has to open a window in which every row integrates at once.

Whether that window exists depends on the sensor timing: an exposure longer than the full readout creates one, and parts with a global reset mode start all rows together instead. Fire the short pulse inside that window to freeze motion.

The tradeoff comes down to motion and the geometric error the task tolerates. Global shutter is the safer default when the camera or object moves during exposure (conveyors, robotics, pick-and-place, strobed illumination, precision measurement): a 200mm/s conveyor moves 0.2mm during a 1ms readout, a real error for a 10µm feature.

Rolling shutter fits when nothing moves during readout (document capture, static label reading, kiosk scanning, cost-sensitive embedded modules). It can still work with motion when readout is short, skew stays inside the task tolerance, or a strobe freezes the scene; speed, motion direction, triggering, correction, cost, and noise move that line.

Shutter type also correlates with lens mount: global shutter cameras in higher-accuracy industrial systems commonly pair with C-mount lenses, whose adjustable iris ring gives depth-of-field control (practical because illumination is usually programmatically controlled). Rolling shutter sensors dominate compact embedded modules paired with M12 lenses for size and weight. The Commonlands M12 vs C-mount vs CS-mount guide covers the full tradeoff.

NIR Sensitivity and Illumination Strategy

Sensor spectral response should follow the illumination strategy, not the other way around. Standard silicon CMOS sensors retain meaningful quantum efficiency into the near-infrared, typically out to 1000–1100nm, but most machine vision cameras ship with an IR-cut filter installed to preserve visible-light color accuracy.

If your system illuminates with 850nm or 940nm LEDs (common for covert lighting, low-visible-light environments, or combined day and night operation), remove the IR-cut filter or specify a NIR-optimized variant. Then confirm the sensor's QE curve at your chosen wavelength rather than assuming uniform NIR sensitivity across parts.

At 850nm, most silicon sensors keep higher QE than at 940nm, at the cost of a faint visible red glow that is sometimes undesirable in public-facing installations. 940nm light is invisible to the eye, but silicon QE there is often around half, with the exact ratio sensor-specific, so it needs brighter illumination or a faster aperture to compensate. Match sensor, filter, and illuminator wavelength as one decision, not three: a NIR-sensitive sensor behind a standard visible bandpass filter gains nothing from the illuminator.

Sensor Format and Lens Coverage

Sensor format is the physical size of the imaging area. The diagonal measurement sets how large a lens image circle you need. If the image circle is smaller than the sensor diagonal, the corners fall outside the rated coverage and receive little to no light, producing vignetting whose severity depends on the lens and how the image circle is defined.

Larger sensor formats capture a wider field of view at a given focal length, or let you use a longer focal length to hold the same field of view with a shallower depth of field. See sensor size and lens compatibility for the format-to-dimension reference and the vignetting math.

A lens rated for a 2/3" sensor leaves the corners of a 1.1" sensor well outside its rated image circle, so severe corner shading is the expected outcome at any aperture; the exact falloff depends on the image-circle definition, aperture, and conjugate, so judge it from relative illumination data rather than the format label alone. Stopping down cannot fix a coverage mismatch: the shortfall is geometric, not a depth-of-field effect.

Always match or exceed the sensor format with the lens specification. Oversizing the lens format covers the diagonal, but coverage alone does not qualify the pairing: check CRA against the sensor's microlens and filter stack, MTF and relative illumination at your pixel pitch, mechanical clearance, and the design conjugate, and expect some added cost.