| Optical Resolution | Image detail, edge definition, contrast, and performance at the intended working distance. | Select a lens that provides sufficient detail for the smallest feature to be inspected. Higher nominal resolution is not useful if illumination, sensor quality, or focus is inadequate. | Compare measured images using the same camera, lighting, distance, and display conditions. Review line-pair or resolution-chart results where available. | High | Keep optical surfaces clean; inspect for scratches, haze, and loss of contrast. |
| Field of View | The visible angle and amount of surrounding anatomy, machinery, or cavity area. | A wider field of view improves orientation and coverage; a narrower field may provide a more detailed view of a small target. Match the lens to the inspection task. | Common endoscope viewing angles include approximately 0°, 30°, 45°, and 70°. Confirm the actual angle and usable image circle before purchase. | High | Clean the objective window carefully because contamination is more noticeable across a wide field. |
| Working Distance and Focus | Distance from the lens to the target and the available depth of field. | Choose a fixed-focus lens when the inspection distance is stable. Choose an adjustable or appropriate close-focus design when the target distance changes significantly. | Verify the minimum and maximum usable focus distances with a real test target, not only with a catalog diagram. | High | Avoid forcing focus mechanisms and protect threads or adjustment rings from debris. |
| Mechanical Durability | Resistance to impact, vibration, bending, insertion force, and repeated handling. | For industrial use, prioritize a protected housing, secure lens retention, strain relief, and a design suitable for the expected insertion environment. | Request documented vibration, shock, insertion-cycle, or cable-flex testing relevant to the application. Check the smallest bend radius of the complete assembly. | High | Use protective caps, storage reels, and controlled insertion procedures; do not exceed the specified bend radius. |
| Sealing and Environmental Protection | Resistance to dust, moisture, immersion, chemicals, and temperature changes. | Select the required ingress protection level only after defining exposure conditions. A water-resistant lens is not automatically suitable for immersion or chemical contact. | Check the stated IP rating, operating temperature, storage temperature, immersion conditions, and chemical-compatibility limitations. | High | Dry the lens after use, inspect seals, and follow the approved cleaning-fluid list. |
| Optical Compatibility | Connection to the endoscope, relay optics, camera coupler, eyepiece, or imaging sensor. | Confirm thread type, mount geometry, flange distance, image-circle size, and mechanical clearance. A visually similar connector may still produce vignetting or focus loss. | Use a dimensioned mechanical drawing and perform a fit test with the exact endoscope and camera configuration. | High | Keep mating surfaces clean and use only approved adapters; avoid cross-threading. |
| Camera and Sensor Matching | Sensor format, pixel size, active area, sensitivity, and image-processing characteristics. | Match the lens image circle to the sensor. An undersized image circle causes dark corners, while an unsuitable lens may waste sensor area or reduce sharpness. | Test for vignetting, chromatic aberration, distortion, and corner sharpness at the intended resolution and frame rate. | High | Recheck alignment after changing cameras, couplers, or adapters. |
| Illumination Efficiency | Light transmission, illumination uniformity, glare, and compatibility with the light source. | Use a lens and light guide combination that produces even illumination without excessive hotspots. Highly reflective targets may require angled lighting or polarization. | Evaluate brightness uniformity, flare, and glare at the actual working distance and with the intended light source. | Medium–High | Clean light-guide interfaces and inspect for cracks, discoloration, or reduced transmission. |
| Chemical and Cleaning Compatibility | Resistance of coatings, adhesives, seals, and housing materials to approved cleaning agents. | Choose materials and coatings that tolerate the planned cleaning process. Never assume that compatibility with water implies compatibility with solvents or disinfectants. | Obtain a written chemical-compatibility list and follow concentration, contact-time, rinsing, and drying instructions. | High | Use lint-free materials and approved solutions; avoid abrasive powders and unverified solvents. |
| Sterilization or Disinfection Method | Whether the lens assembly supports the required cleaning, high-level disinfection, or sterilization process. | For medical applications, select only a configuration whose reprocessing instructions explicitly match the facility’s validated procedure. | Verify compatibility with the required method, temperature, pressure, exposure time, and number of reprocessing cycles. | Critical | Document each cycle and inspect seals, coatings, and image quality at scheduled intervals. |
| Temperature Performance | Operating and storage limits, thermal shock resistance, and focus shift with temperature. | Allow the lens to stabilize when moving between environments with a large temperature difference. Select a wider temperature range for outdoor, engine, or process inspections. | Check specified operating and storage ranges, then test image focus and sealing after the expected thermal transition. | Medium–High | Prevent condensation; store the lens dry and capped when it is not in use. |
| Distortion and Measurement Accuracy | Geometric distortion, scale accuracy, and suitability for dimensional inspection. | For measurement work, use a calibrated system and a lens with documented distortion performance. Do not use an uncalibrated visual lens for precise dimensional conclusions. | Validate against a certified reference target at the intended distance and field position; record calibration conditions. | High | Repeat calibration after impact, lens replacement, major temperature changes, or camera relocation. |
| Serviceability and Spare Parts | Availability of replacement windows, seals, adapters, cables, cleaning tools, and repair procedures. | Prefer a design with documented service procedures and replaceable wear components when downtime or contamination risk is costly. | Confirm spare-part availability, repair turnaround expectations, inspection intervals, and warranty terms before approval. | Medium–High | Maintain service records and replace damaged protective components promptly. |
| Routine Cleaning and Storage | Daily cleaning steps, drying requirements, storage temperature, and protection from dust or impact. | Choose a lens that can be cleaned consistently by the operating team without complex tools or excessive disassembly. | A practical procedure should cover pre-cleaning, approved solution, rinsing, drying, visual inspection, protective caps, and storage. | Medium–High | Clean after each use when exposed to residue; store in a padded, dry, dust-protected container. |
| Acceptance Testing Before Purchase | Whether the lens meets actual image, fit, environmental, and workflow requirements. | Run a documented trial using the intended endoscope, camera, light source, target materials, cleaning process, and operators. | Record focus range, field of view, image uniformity, distortion, connector fit, cleaning outcome, and any handling limitations. | Critical | Use the test results as the baseline for future preventive-maintenance inspections. |
