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.
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.