[rubylark]

Interesting, this eye drop seems to just do the opposite of what those eye dilation drops used at the eye doctor. It makes sense considering that dilation drops make it impossible to read things up close that an inverted purpose drop could help people with weak pupil response.

[kortex]

In optics, there's a thing called the circle of confusion (1). It's the locus of points that maps to a single point source of photons. A "perfect" focus maps a point source to a point on the image: perfect contrast. Ability to focus is basically how tight you can get this circle, for a focal distance. (this is all super simplified, perfect lenses, no aberration, etc).

The smaller the aperture, the more constrained the light field, thus the smaller the circle of confusion (at the expense of light collection). That's how pinhole cameras work in fact.

Shrinking the aperture also increases the depth of focus. Pinhole cameras have ~∞ depth of field because there is ~1 path every photon can take (ignoring hole width, diffraction, etc).

1 - https://en.m.wikipedia.org/wiki/Circle_of_confusion

[toss1]

Yup, and this makes me think that the advice to put brighter light on your reading to make things sharper doesn't work because of greater light availability, but because it provokes the pupil to narrow and increase the pinhole camera effect -- or more to the point, not that the bright light doesn't itself help, but how much is due to more light vs provoking smaller pupil opening?