| Meaning of “2.5 inch” | A 2.5-inch lens format generally indicates an image circle of about 63.5 mm; it does not mean the focal length is 2.5 inches. | Confirm the lens’s stated image-circle coverage. The sensor’s diagonal must fit within it, preferably with some margin to accommodate tolerances and avoid corner shading. |
| Sensor format and approximate active area | 1-inch: 13.2 × 8.8 mm; APS-C: approximately 23.5 × 15.6 mm; full-frame: 36 × 24 mm. | Compare the sensor’s actual active dimensions and diagonal with the lens image circle. Format labels are approximate and can vary between sensors. |
| Sensor diagonal check | Diagonal = √(sensor width² + sensor height²). A 36 × 24 mm sensor has a diagonal of about 43.3 mm. | A lens with a 63.5 mm image circle can geometrically cover that example sensor. Check the lens data sheet for usable image quality across the full sensor area, not just nominal coverage. |
| Field of view (FOV) | At 0.5× magnification, an 13.2 mm-wide sensor covers about 26.4 mm across the object plane: FOV ≈ sensor width ÷ magnification. | Calculate FOV using the sensor dimension in the direction being scanned. Include any required edge margin and verify the result at the actual working distance. |
| Magnification | Magnification ≈ sensor width ÷ required object width. A 13.2 mm sensor covering a 26.4 mm object width requires approximately 0.5×. | Choose a lens that supports the required magnification while maintaining adequate image quality. Do not assume focal length alone determines magnification or working distance. |
| Pixel size and object sampling | With 3.45 µm pixels at 0.25× magnification, object-plane sampling is approximately 13.8 µm per pixel: pixel size ÷ magnification. | Compare object-plane sampling with the smallest feature to be detected. A feature spanning only one or two pixels may be difficult to resolve reliably; optical performance, contrast, and processing also matter. |
| Lens resolving power | Resolution depends on lens performance, sensor pixel pitch, magnification, focus, aperture, and wavelength. | Check resolution or MTF specifications at the sensor’s pixel scale and across the required image area. Center-only performance may not represent the corners. |
| Working distance and focus range | Working distance is measured from the front of the lens to the object and depends on the optical design and focus setting. | Confirm that the lens can focus at the scanner’s available distance, including fixture clearance and any protective window. Request the working-distance range at the intended magnification. |
| Scanner motion and exposure | For a moving object, image blur increases with object speed and exposure time. | Match exposure and scan speed to the required sharpness. Consider synchronized illumination or a line-scan setup where continuous motion is part of the application. |
| Mount and mechanical clearance | Mount type, flange distance, lens diameter, and camera-body clearance are system-specific. | Verify the camera interface, adapter requirements, focus-ring access, and clearance inside the scanner before ordering. |
| Aperture, illumination, and depth of field | Stopping down can increase depth of field but reduces the light reaching the sensor; very small apertures can also reduce fine-detail contrast through diffraction. | Balance depth of field, exposure time, illumination, and resolution. Test at the working aperture rather than relying only on the lens’s best-case specification. |
| Final system validation | Test with the actual sensor, scanner distance, target, lighting, and scan speed. | Check FOV, corner sharpness, distortion, shading, focus repeatability, and detection of the smallest required feature across the complete scan area. |
