Diffractive Lens vs. Google Cardboard’s Asphere

As I mentioned in my last post, Google Cardboard is the interim hardware for developing Daydream apps.  The lenses look very similar to those used in the Oculus Rift development kits, although a bit faster and smaller in diameter.  The field of view is also a bit smaller.  On-axis, the MTF is nearly perfect, but off axis (with the eye still centered in the eyebox), it’s quite poor.

Diffractive lens designGoogle Lens MTF

Now, if I make one surface diffractive and reoptimize, the MTF improves dramatically.  Much of the improvement comes from chromatic correction, including the longitudinal variety, which cannot be corrected in image processing.

DO lens design modulation transfer function