	Machine Vision Systems

Lens Characteristics

Distortion

Lens with Minimal Distortion for High-precision Measurement

Lenses with a short focal distance have high image distortion. Fish eye lenses, with a visual field of 180°, have very high image distortion.

Among the lenses that we carry, the 50 mm model achieves the least amount of distortion. Minimum distortion lenses are preferred for high precision measurements.

Depth of Field

Vertical Deflection

Depth of field is linked to the range of focal distance. The deeper the depth of Field, the greater the lens tolerance against vertical deflection.

Conditions Deepening the Depth of Field

	Images with a short focal distance and large working distance have a large depth of field.
	It should be noted that the depth of field becomes shallower if a photograph ring or macro lens is used. Small apertures increase the depth of field.
	To facilitate focusing, the aperture may be closed and the object illuminated brightly.

Telecentric Lens

Special Lens for High-Precision Measurement

Distortion or depth of field is not a big issue for general inspections such as presence check or size detection. Even for measurements, a macro lens is good enough if the working distance is fixed. However, telecentric lenses provide high magnification, low distortion and a long depth of field. Although costly and slightly larger than conventional lenses, telecentric lenses allow highly accuracte measurements. The following figure shows the configuration.

Unlike a normal lens, parallel optical axes means the workpiece size remains unchanged, even in the event of vertical deflection.

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