How to Calculate the F-stop of the Human Eye

Your eye has more in common with your DSLR than you might think

What if our photos looked as good as our eyes could see?Popular photography

Every photographer has had a moment when they wished their eye was a camera. It seems that no matter how hard we try, there are always some images and experiences that just look better through our own eyes, than through our camera. There are a lot of factors that go into how the eye takes in and processes information, but the F-number for your eye can easily be calculated using the human eye's focal length (~22mm) and physical aperture size.

The eye’s pupil can be as large as 6–7 mm wide open, which translates into the maximum physical aperture, meaning the f-number of the human eye varies from about f/8.3 in a very brightly lit place to about f/2.1 in the dark. According to the incoming rays of light (what we actually see), the focal length of the eye is a bit longer, resulting in minimum f-number of f/3.2, but again, that’s different that f/3.2 on your DSLR, because the eye cannot be considered an ordinary air-filled camera since it’s filled with light refracting liquid.

Still interesting to think about the next time your images fall short of what you saw with your eyes.