Skip to main content
2 of 8
added 598 characters in body
mattdm
  • 143.6k
  • 52
  • 421
  • 745

The blur from a wider aperture is distinct from the blur from motion. I'm going to crib from my answer to an earlier question on aperture:

When the aperture is very small, the admitted light is highly "collimated", which is a fancy way of saying "all the rays are nicely parallel to each other". This results in a sharp focus for all the light that comes in. When the aperture is more open, only the rays which closely match the focus point are collimated — which means that whatever you've focused on is sharp, but farther or closer parts of the scene will be increasingly blurry.

Basically, the smaller the aperture, the more restricted-to-exactly-in-focus the light is. A bigger aperture lets in more light, but the "price" is that it's less controlled.

This surely happens with the human eye as a lens as well. I think it's just really hard to control your experiment, since you can't actually snap a picture to compare side by side. In the time between evening and midday — or even in the half hour it takes your eyes to acclimate to a dark room — you lose the perfect memory of how much blur there was. This is further complicated by the fact that your brain is working very hard to correct all defects from the eyes and present a mental model of the entire world in perfect focus. (That's what the brain part of the human vision system does.)

mattdm
  • 143.6k
  • 52
  • 421
  • 745