Placement-tolerant optics for a smartphone dermatoscope

Challenge

The existing three-lens design lost image quality once the phone camera sat a fraction of a millimeter off center, and the outer field collapsed as that offset grew. Real users cannot seat a phone that precisely. Every mechanical interface, from lens thickness to the phone case, had to stay the same.

Approach

We traced the root cause to the phone aperture acting as a moving system stop, then re-optimized only the molded asphere shapes against a model with the phone deliberately misplaced. A Bayesian optimization campaign scored candidates directly on MTF instead of wavefront proxies. A ghost screen of the internal reflection paths, an AR coating decision, and a full structural-thermal-optical tolerance suite followed.

Result

Worst-case contrast across a sub-millimeter placement box improved about 100x while the barrel, retention, and case carried over unchanged. The adopted design passed the tolerance load cases.

Key figures

• ~100x

  worst-case contrast under sub-millimeter phone misalignment

• ~300x

  lower flare peak at the sensor

• ~15%

  light throughput