Machine Vision Lenses for Quality Inspection

Start with your smallest defect size and work backward. Calculate the pixels needed to detect it reliably (3 to 5 pixels per defect minimum), which sets your sensor resolution requirement. Working distance is usually fixed by your physical setup, and it determines focal length through the rectilinear focal length equation. Aperture then sets your depth of field. Work through the specifications in this order: defect size, sensor resolution, working distance, focal length, aperture, sensor format.

Only if you are measuring dimensions where perspective error is unacceptable, such as checking heights or diameters from above. For most surface defect detection, barcode reading, seal checks, and print verification, a standard entocentric C-mount or M12 lens works and costs significantly less. Telecentric lenses require precise working distance control and have a limited field of view. Commonlands does not currently sell telecentric lenses; reserve them for true metrology applications through a specialist vendor.

Yes, for embedded inline inspection where size and cost are the primary constraints and the inspected surface is flat or near-flat. Most M12 lens models cover sensors up to 1/1.8", with select models reaching 1/1.7" to 1/1.6". For larger sensors, precision measurement requiring an adjustable aperture, or depth-of-field control on curved or uneven surfaces, C-mount is the better tool: its iris ring makes stopping down for depth of field practical when illumination is programmatically controlled.

Working distance directly determines focal length: EFL = (working distance × sensor width) / field-of-view width. Shorter working distance requires a shorter focal length at a given field of view and sensor size. Longer working distance requires a longer focal length but provides more physical clearance for conveyor hardware, robot arms, or enclosures. Working distance is usually constrained by your physical setup before you ever open a lens catalog.

For flat parts at a fixed working distance, open the aperture for maximum light throughput, MTF permitting; many industrial lenses are aberration-limited wide open and reach peak sharpness one to three stops down. For 3D parts or components with varying heights, stop down to increase depth of field. Diffraction sets a practical ceiling: above F# ≈ 2 × pixel_pitch_µm, diffraction softening typically exceeds the DOF and resolution gain from stopping down further. For a sensor with 3.45 µm pixels, that ceiling is roughly F/7.

When the packaging or label surface is not flat. Bottles, pouches, blister packs, and formed containers create height variation of a few millimeters across the inspection zone, which pressures depth of field at wide apertures. An adjustable iris lets you stop down and recover exposure with illumination power, a routine tradeoff since inspection illumination is usually programmable. M12 lenses typically ship with a fixed aperture, which removes that option and is fine for flat surfaces but a real constraint on curved or uneven ones.