Line scan imaging is the least forgiving corner of machine vision. A 16K camera runs a φ82mm image circle, the web moves while you expose, and a lens that looks perfect on paper can still cost you 30% contrast at the edges. This guide covers the four numbers that actually decide whether a line scan lens works in your machine — and the three mistakes we see most often in RFQs.
1. Start From the Sensor, Not the Focal Length
Line scan sensors are specified by pixel count and pixel size, and those two numbers define the image circle you need:
| Sensor format | Pixel size | Active width | Required image circle |
|---|---|---|---|
| 2K | 7µm / 10µm | 14.3 / 20.5 mm | φ30 mm class |
| 4K | 7µm | 28.7 mm | φ32 mm |
| 8K | 5µm | 40.0 mm | φ46 mm |
| 8K | 7µm | 56.0 mm | φ62 mm |
| 16K | 5µm | 81.9 mm | φ82–φ90 mm |
Rule of thumb: a larger circle always works downward. An 8K7µm lens (φ62mm) will cover a 4K camera; the reverse produces vignetting. If you plan to upgrade the camera in 18 months, buy the circle you will need then, not the one you need today.
2. Magnification Comes From the Web Width
Example: an 8K5µm camera (40mm active) inspecting a 400mm-wide lithium electrode → 40 / 400 = 0.1X. The same camera on a 1200mm-wide glass sheet → 0.033X. Both are valid; they simply sit in different lens families.
Our LS families are grouped by the magnification band they are corrected for — roughly 0.01X–0.1X for wide-web and large-format work, 0.2X–0.5X for general web inspection, and 0.7X–3X for high-resolution small-part scanning. Selecting outside the corrected band is the single most common cause of a “soft at the edges” complaint.
3. Working Distance Is a Mechanical Constraint, Not an Optical One
Every CLARIOPTICS LS datasheet lists three distances: the center working distance, the WD range over which the specified MTF holds, and the object-to-image (O/I) conjugate distance. Machine designers habitually use the first and ignore the third — then discover the camera body collides with the frame.
Always check O/I against your fixture envelope before you freeze the layout. If the conjugate is too long, the usual fix is a shorter focal length at the same magnification, not a different mechanical redesign.
4. Mount, Flange-Back and Rotation
M42 and M58 cover most 4K and 8K configurations; M72, M90 and M95 appear on large-format 16K and high-magnification bodies; F-mount persists on some 8K and 100MP setups. Beyond the thread, verify two things buyers forget:
- Flange-back distance — the lens must reach focus on your camera's sensor plane. Adapters exist but add tolerance stack-up.
- Rotation / phase adjustment — on a line scan camera the sensor line must be parallel to the lens's sharpest axis. A lens with a rotation-adjustable mount turns a two-hour alignment job into ten minutes.
Three Mistakes We See in RFQs
Mistake 1 — specifying focal length before FOV
“We need a 60mm line scan lens” is not a requirement; it is a guess. Give us the sensor, the scan width and the available WD, and the focal length falls out of the calculation.
Mistake 2 — ignoring the lighting geometry
A coaxial or line-light setup changes the effective aperture and can introduce specular artifacts that no lens can fix. Tell us the illumination type and we will flag it before you build.
Mistake 3 — no tolerance for web flutter
If the web moves ±2mm vertically, you need depth of field, not just resolution. That usually means closing the aperture one stop and accepting the light loss, or moving to a longer WD with a higher-power line light.
Get a Selection Proposal
Send us your camera model, scan width and working distance envelope. Our engineers return a complete proposal — recommended model, magnification, WD range, mount and lighting note — within one business day. Start here → or run the numbers yourself in the Lens Selector.