Thanks to Kragen Sitaker for sending me feedback about my sunlight experience. He writes:
This is painful at first because too much light enters your eye; after a while, your iris adjusts, your pupil shrinks, and the light level in your eye falls to a tolerable level. One side-effect of your pupil shrinking is that your depth of field increases. (If you’re a photographer, you know this happens when you go to a smaller aperture (f/stop).) Intuitively, your eye is becoming more like a pinhole camera, for which everything is in focus.
Aha! I’ll have to work this into my worldview some more…