The reason for this seems to be 1) extended depth of field with a smaller pupil in bright sunlight (smaller aperture) that keeps objects at a wider range in fo

The reason for this seems to be 1) extended depth of field with a smaller pupil in bright sunlight (smaller aperture) that keeps objects at a wider range in focus 2) biochemical cascade responding to certain wavelengths in sunlight that produce a “stop growth” signal in the retina