Autofocus of Iris Patterns Using a Triangle Aperture

This paper shows that, by simply adding a triangle aperture (TA) in front of a camera lens, iris autofocus can be easily achieved. Through the TA, the corneal reflection of a light source forms a triangle glint on the image plane. The size and orientation of the glint can be used to infer the amount and the direction of the focus adjustment. A gradient-descent autofocus control law is proposed for uncalibrated lenses. Results from theoretical analysis and real experiments show that the proposed method is more efficient and accurate than the conventional circular aperture approach.