If something really small with eyes, like an ant, were to stumble upon something very small humans can’t see, would they be able to see it?
In: Biology
# ELI5
Small organisms with eyes can’t see small things humans can’t see because their sight isn’t as good. Small eyes can’t have as good sight as large eyes can have because light bends while passing through small apertures and that distorts the image.
# More elaborate explanation
Human eyes have certain aperture (the hole through which the light passes) size and it determines how much light is diffracted while passing through the aperture. [Diffraction](https://en.wikipedia.org/wiki/Diffraction) is bending of light waves while passing through an aperture. Light diffracts more in smaller slits. The size of human eye aperture allows to [see with the resolution of around 1 angular minute](https://en.wikipedia.org/wiki/Naked_eye#Basic_properties). Smaller animals with non-compound eyes therefore have worse sight than that.
Insects use [compound eyes](https://en.wikipedia.org/wiki/Compound_eye), where each light sensor is in its own tube and with its own lens and detects only light travelling rougly in the direction of the tube. These eyes are simpler in construction than non-compound eyes and have low resolution. But, if insects had non-compound eyes, they wouldn’t see better because their eyes are so small that the diffraction would make the eye’s resolution as low as it’s in their compound eyes.
# Caveat
It could be said that smaller eyes can get closer to the seen object, therefore see it in a larger angle. An insect with could see an object as small as one ommatidium in its eye, which could be very small in small insects, if it was placed right next to the eye. But then it could be said that humans can see tiny [eye floaters](https://en.wikipedia.org/wiki/Floater), particles floating in the vitreous body of an eye, which can get so close to the retina that they can be seen although they are so small.
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