I saw a comic about this once (xkcd, probably?) and going by the scene in the movie, where Legolas has human sized eyes, they deduced that Middle Earth must have an exotic atmosphere

Gives any what? Sorry I can't read that heavily obscured text.

It depends on the atmosphere. On earth, the average 'size' of the atmospheric distortion experienced by a photon over 15 miles would far exceed the angular resolution of any pupil-sized aperture. This is a very simple explanation which groups a number of propagation effects broadly under the term "distortion." Even without atmospheric distortion, there is a limit to the "information" a given aperture can resolve due to purely thermal noise. In theory, if you have an aperture temperature of absolute zero, the thermal resolution is infinite, but also then there is no process by which information can be generated by an I cident photon.