Selection Guides
Decide when telecentric optics are justified by measurement tolerance, part height variation and fixture repeatability.
Direct answer
A telecentric lens is justified when perspective error from part height or position changes can alter the measurement result. Use it for gauge-style edge, hole, gap and diameter inspection only when tolerance risk supports the cost and size.
Use a telecentric lens when perspective error from part height or position would change the measurement result, especially for edges, holes, pins, gaps and diameters.
They reduce perspective error, but they do not solve weak edge contrast, loose fixtures, poor lighting or a tolerance that has not been defined.
Provide object size, tolerance, height variation, sensor size, working distance, mechanical clearance, lighting route and sample edge photos.
A regular lens changes apparent size when the part moves closer or farther from the camera. Telecentric optics reduce that perspective shift for edges, holes, pins, gaps and diameters where a few pixels can change pass/fail.
If the inspection target is only presence, label checking or a large visual defect, a standard FA lens may be the practical route. Telecentric cost is justified when part height variation, fixture tolerance or Z-position change would create measurement error.
Telecentric lenses are less forgiving than ordinary lenses. Object size, sensor size, magnification, working distance and mechanical clearance should be checked as one set before model selection.
A telecentric lens does not fix weak contrast or loose fixturing. Measurement projects should test the lens with the real edge, backlight route, exposure, threshold method and production fixture before acceptance.
How to test before buying
Test the telecentric lens with the intended backlight or surface light, real part height variation and the final threshold method before accepting the measurement route.
Decision checks
Use telecentric optics when Z variation changes apparent size with a normal lens.
Telecentric is safer when the acceptance rule depends on a small edge, hole, diameter or gap tolerance.
Object-side FOV and camera sensor must match the lens magnification.
Decision table
| Factor | Practical rule | RFQ impact |
|---|---|---|
| Part height variation | Use telecentric optics when Z variation changes apparent size with a normal lens. | Send expected part height range, tolerance and fixture repeatability. |
| Measurement tolerance | Telecentric is safer when the acceptance rule depends on a small edge, hole, diameter or gap tolerance. | Send tolerance, target feature and required repeatability. |
| FOV and sensor size | Object-side FOV and camera sensor must match the lens magnification. | Send full part size, required measured area and camera model if fixed. |
| Lighting route | Backlight is common for silhouette measurement; coaxial or structured lighting may be needed for surface marks. | Send target feature photos and whether top-surface detail matters. |
| Cost control | Use a regular low-distortion lens when perspective error is not the limiting factor. | Prevents over-specifying optics for simple inspection. |
Application proof
Small parts need fast dimensional verification without slow manual measurement or inconsistent operator positioning.
Small connector features require stable contrast, low distortion and repeatable part positioning before a pass/fail threshold can be trusted.
Wide moving material needs even illumination, encoder synchronization and enough line rate to avoid missing small defects.
Common mistakes
Factory handoff
The factory route review starts by checking whether the image can be made stable with lighting and fixture control. Then the camera, lens, reader or 3D sensor route is sized against speed, resolution, interface and installation constraints.
If you already have a Keyence, Cognex, Basler, OPT, LMI, Hikrobot or barcode-reader reference, include it as a reference model. Deyi Vision uses it to understand the application class; final selection still depends on real samples and production limits.
Guide to RFQ
Use the guide to frame the question, then send the details so engineering can recommend a route.
Request engineering RFQGuide FAQ
It is used for repeatable dimensional inspection where perspective error from part height or position changes would affect the measurement.
No. It is better for measurement stability, but it is larger, more expensive and less flexible. For presence, label or general defect inspection, a regular low-distortion lens may be enough.
Send object size, sensor size, working distance, tolerance, part height variation, target edge or feature, lighting condition and fixture constraints.
