How far can flies see?

Human eyes are spherical, but flies' eyes are hemispherical. Flies' eyes can't move like human eyes. When a fly looks at something, it turns its eyes to the object by its neck and body. The fly's eyes have no eye sockets, eyelids and eyeballs, and the cornea on the outer layer of the eyes is directly connected with the surface of the head. From the outside, the surface of fly eye (cornea) is smooth and flat. If you put it under a microscope, people will find that the fly eye is composed of many small hexagonal structures. Every small hexagon is a small eye. Scientists call it small eyes. In a fly's eye, there are more than 3000 small eyes, and a pair of fly's eyes have more than 6000 small eyes. This kind of eye, which consists of many small eyes, is called compound eye. Every small eye in a fly's eye has its own system, including an imaging system composed of cornea and lens dimension, a retina composed of photosensitive visual cells, and an optic nerve leading to the brain. So every little eye sees things separately. Scientists have done experiments: peeling off the cornea of a fly as a photographic lens and taking pictures under a microscope can take hundreds of identical images at a time. There are many animals with compound eyes in the world. Almost14 animals use compound eyes to see things. Common insects such as dragonflies, bees, fireflies, scarabs, mosquitoes, moths and crustaceans have compound eyes. Scientists are interested in fly eyes because they have many amazing functions.