Digital booths
When the centre is sharp but the strip edges are soft
Test whether edge softness follows the lens field rather than guest distance.
A booth camera can focus correctly near the centre while faces near the frame edge look softer. One possible optical cause is field curvature: the best-focus surface is not perfectly flat. It is different from a guest leaning closer or the camera missing focus entirely.
Compare points at equal distance
Place a flat detail target parallel to the camera at the portrait plane. Include a fine pattern in the centre and near both sides, then capture without changing focus. If the centre is crisp but both edges lose contrast in a similar way, the lens field may contribute. If one edge alone is soft, first check camera tilt or target alignment.
Evidence: Optics manufacturer application note
Separate curvature from distortion
Distortion bends or shifts straight image geometry; it does not necessarily mean that detail is out of focus. Field curvature affects which plane is sharply rendered. Photograph a grid and a detail chart together: bowed lines indicate geometry change, while softened edge marks indicate a focus or contrast issue.
Evidence: Optics manufacturer application note
Check practical framing
Keep guests away from the extreme image corners during a repeatable test and compare the saved strip. For a permanent booth, use the target at the exact camera-to-subject distance and intended crop. A generic lens chart cannot certify performance after a crop, focus change or protective window is added.
Evidence: Optics manufacturer application note
Sources & further reading
Sources for the specific facts and product descriptions above. Our worked examples, interpretations and practical suggestions are original editorial guidance.
- Edmund Optics, Comparison of Optical AberrationsOptics manufacturer application note