| Object-Side and Image-Side Telecentricity | Critical Prefer a design with low angular deviation on both sides; the acceptable error depends on measurement tolerance and field size. | Confirm whether the lens is truly bi-telecentric rather than only object-space telecentric. Compare telecentricity error across the full specified field and working-distance range. | Optical specification sheet, telecentricity-error plot, measurement conditions, and a sample image taken at different object distances. |
| Magnification Stability | For dimensional inspection, magnification should remain effectively constant when the object moves within the stated depth range. A tolerance of about 0.1% or better is commonly targeted for demanding metrology. | Compare magnification variation, nominal magnification, and whether the stated value applies at the calibrated working distance or throughout the usable depth of field. | Certified calibration data, magnification-versus-distance curve, and dimensional test results using traceable artifacts. |
| Optical Distortion | High-precision inspection systems commonly seek distortion below 0.1%; applications requiring tighter dimensional accuracy may require substantially lower values. | Check maximum distortion, distortion type, measurement field, and whether the value is measured optically or corrected through software. | Distortion map, calibration report, raw image examples, and details of any software correction or polynomial model. |
| Field of View and Sensor Coverage | Field of view is determined by magnification and sensor size. The image circle should fully cover the selected sensor without corner shading or loss of resolution. | Compare compatible sensor formats, image-circle diameter, usable field, and the relationship between magnification and field of view. | Optical layout drawing, sensor-compatibility table, illumination test images, and corner-resolution measurements. |
| Resolution and MTF | Resolution must support the smallest feature to be inspected. MTF should be evaluated at relevant spatial frequencies across the center and edges of the field. | Compare MTF at multiple field positions, operating wavelengths, apertures, and working distances rather than relying only on a center-field resolution value. | MTF charts, test wavelength, aperture setting, image height, test target type, and measured-versus-modeled performance data. |
| Depth of Field | Bi-telecentric lenses are often selected for stable dimensional imaging, but usable depth of field still depends on magnification, aperture, illumination, and allowable blur. | Compare depth of field at the required resolution and measurement tolerance. Avoid comparing figures measured with different blur criteria. | Depth-of-field calculation, focus-stack images, allowable-circle-of-confusion value, and test results at the intended aperture. |
| Working Distance | Working distance should provide sufficient clearance for parts, fixtures, lighting, and actuators. Common machine-vision designs may range from several dozen to several hundred millimetres. | Compare nominal and usable working distance, mechanical clearance, front-element position, and performance changes near the limits of the specified range. | Mechanical drawing with tolerances, working-distance performance data, and clearance recommendations for coaxial or ring lighting. |
| Numerical Aperture and Light Throughput | Higher numerical aperture can improve resolution and light collection but generally reduces depth of field and may increase sensitivity to alignment. | Compare NA, f-number, aperture adjustment range, transmission, and the balance between resolution, exposure time, and depth of field. | Aperture specification, transmission curve, illumination recommendations, and sample exposure settings at the intended camera configuration. |
| Spectral Compatibility | For visible-light inspection, performance is commonly specified across approximately 400–700 nm. Extended visible, near-infrared, ultraviolet, or monochromatic use requires dedicated verification. | Compare wavelength range, chromatic aberration control, coating design, and performance when used with the selected lighting wavelength. | Transmission curve, spectral MTF data, chromatic-focus-shift data, coating information, and wavelength-specific test images. |
| Chief-Ray Angle and Illumination Uniformity | A low and consistent chief-ray angle is beneficial for sensors with direction-sensitive pixels and for uniform telecentric illumination setups. | Compare chief-ray-angle data, relative illumination across the field, vignetting, and compatibility with coaxial, dome, or backlighting systems. | Relative-illumination chart, chief-ray-angle data, flat-field image, and recommended lighting geometry. |
| Mechanical Interface | Mounting thread, flange distance, adjustment access, and housing rigidity should match the camera and machine structure. | Compare mount type, outer diameter, length, mass, filter access, locking features, and the availability of adapters or custom mechanical interfaces. | Dimensioned CAD drawing, interface-control document, tolerance table, and vibration or mounting guidance. |
| Calibration and Traceability | For metrology, calibration should be linked to known standards and performed under documented environmental and optical conditions. | Compare calibration method, uncertainty reporting, reference artifacts, calibration interval, and whether calibration files can be supplied for machine integration. | Calibration certificate, uncertainty budget, traceability statement, test procedure, and sample measurement report. |
| Manufacturing Consistency | Production-to-production variation should be controlled for magnification, distortion, telecentricity, and focus position. | Compare stated tolerances, incoming inspection, final optical testing, serial-number traceability, and availability of lot-specific test data. | Quality-control plan, inspection records, acceptance criteria, and statistical process-control information where available. |
| Environmental Reliability | Industrial installations may require resistance to temperature changes, vibration, dust, and humidity. Requirements should be defined by the machine environment. | Compare operating and storage temperature, humidity limits, vibration resistance, sealing level, thermal focus shift, and service-life expectations. | Environmental test reports, ingress-protection rating where applicable, thermal-drift data, and installation limitations. |
| Customization Capability | Special applications may require non-standard magnification, working distance, spectral band, mount, filter, or image-circle dimensions. | Compare engineering support, prototype capability, optical redesign limits, minimum order requirements, sample approval process, and change-control procedures. | Non-disclosure and development process, prototype schedule, optical simulation, design-review documents, and first-article inspection report. |
| Lead Time and Supply Continuity | For global projects, predictable production and replenishment are often more important than the shortest initial quotation. | Compare standard versus custom lead times, production capacity, component availability, forecast requirements, packaging, and spare-unit recommendations. | Formal quotation, delivery schedule, capacity statement, continuity plan, packaging specification, and replacement-part policy. |
| Documentation and Technical Support | Complete documentation should enable optical selection, mechanical integration, calibration, operation, and troubleshooting without undocumented assumptions. | Compare the quality of datasheets, drawings, manuals, optical data, integration guidance, response time, and support during commissioning. | Sample technical package, application notes, installation manual, response-time commitment, and documented escalation process. |
| Total Cost of Ownership | Purchase price should be evaluated together with calibration, adapters, lighting compatibility, integration labour, replacement risk, and expected service life. | Compare delivered cost, warranty, calibration services, repair policy, spare availability, shipping terms, taxes, and cost of future design changes. | Itemized quotation, warranty terms, service-rate card, repair turnaround time, shipping terms, and lifecycle-cost estimate. |