What does it mean when wildlife biologists say that “an eagle can see a rabbit in a field from miles away”? Does this imply that their vision is automatically more zoomed in? Do they have better than 20/20 vision, or is their vision simply clearer?

Question

What does it mean when wildlife biologists say that “an eagle can see a rabbit in a field from miles away”? Does this imply that their vision is automatically more zoomed in? Do they have better than 20/20 vision, or is their vision simply clearer?

In: Biology

Answer 1

Bigger eyeballs with larger pupils. Ever wonder why telescopes have a large diameter? It improves their angular resolution – what the angular separation of two objects has to be for them to be resolved as two separate objects. The bigger the aperture, the smaller the angle between two objects can be such that they can be resolved as separate objects. This is based on diffraction of light passing through the aperture. Smaller apertures increase diffraction and decrease resolution. If you are a photographer, you know that closing down your aperture too much will give you blurry photos due to diffraction. Notably, this is also wavelength dependent as well. When the wavelength increases, the aperture diameter needed for equivalent resolution also increases. Since radio waves are enormously longer wavelength than visible light, radio telescopes have to be enormous to have decent resolution. The physics is a little above the 5yo level, LOL. I taught about this for 30+ years as a physics prof (recently retired.)

Have a look at:

[http://hyperphysics.phy-astr.gsu.edu/hbase/phyopt/Raylei.html](http://hyperphysics.phy-astr.gsu.edu/hbase/phyopt/Raylei.html)

[https://phys.libretexts.org/Bookshelves/College_Physics/College_Physics_1e_(OpenStax)/27%3A_Wave_Optics/27.06%3A_Limits_of_Resolution-_The_Rayleigh_Criterion](https://phys.libretexts.org/Bookshelves/College_Physics/College_Physics_1e_(OpenStax)/27%3A_Wave_Optics/27.06%3A_Limits_of_Resolution-_The_Rayleigh_Criterion)

Here is a really great interactive simulation I used with my students. It lets you vary the separation of the objects and the wavelength of the light to see how it affects the resolution of the two objects. You may have to reload the page to get the simulation to run properly.

[https://www.olympus-lifescience.com/en/microscope-resource/primer/java/imageformation/rayleighdisks/](https://www.olympus-lifescience.com/en/microscope-resource/primer/java/imageformation/rayleighdisks/)