Line scan systems fail more often on integration than on optics. Before you swap the lens, walk through these eight checks — ordered by how often each turns out to be the real cause.
1 — Focus Is Set Along the Scan Line, Not at One Point
An area camera focuses at a point; a line scan lens must be sharp across the whole scan width. Focus at the centre, then re-check sharpness at both ends of the line. Our LS series holds field curvature low enough that one focus works end to end — but only if check 2 is also true.
2 — Lens Axis Square to the Web
A tilted axis shows up as one edge of the image sharper than the other, and as width-dependent magnification. Shim the camera mount until a precision straight-edge images the same width at both ends of the scan.
3 — Square Pixels: Encoder Scaling
If the web advances 12µm per line while your pixel is 7µm, every object is stretched 1.7× along the scan direction. Set encoder scaling so that millimetres-per-line equal the pixel pitch; geometry is then true in both axes and measurements do not need direction-dependent correction.
4 — Exposure Time vs Web Speed
At 300 mm/s and 7µm pixels, exposure must stay under about 23µs or the image smears along the scan direction. If you cannot expose that short, add light or open the aperture — do not slow the production line to suit the vision system.
5 — Illumination Aperture Matches the Lens Field
The light must cover the full scan width at the object plane, uniformly, in the geometry (bright field / dark field) your defect class needs. A light 10% narrower than the lens field darkens the image edges and masquerades as a “lens problem”.
6 — Image Circle Covers the Sensor
Match the line-scan format to the image circle: 4K×7µm needs φ32mm, 8K5µm needs φ46mm, 8K7µm needs φ62mm, 16K5µm needs φ82–φ90mm. A larger-format lens used on a smaller sensor is fine; the reverse vignettes.
7 — F-Number: Depth of Field Across Web Flutter
Web flutter consumes depth of field in the Z direction. Set the F-number so the depth of field covers the flutter envelope, then verify resolution at that F-number — not wide open on the bench.
8 — Thermal and Vibration Drift
Re-check focus after the station reaches operating temperature, and lock the focus and iris screws — standard on our FA and LS barrels — so vibration cannot walk the settings away.
To shortlist lenses by sensor format and image circle, use the line scan series tables or the lens selector; the line scan selection guide covers the optical math in more depth.
Still Failing?
Send us the camera model, web speed, pixel pitch and the defect class — we return a complete setting proposal with sample-shooting advice within one business day. Start here →