I once heard a biologist remark that if we were to run across any sort of complex alien life form they would probably have recognizable eyes, because eyes, of various types, have evolved separately many times (i.e., mammalian eyes vs. insect compound-eyes). In fact she gave a specific number of time, a single digit.
So what are these different types of eyes? What are the differences between them and when and where did they evolve?
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Unless I’m mistaken, Octopuses (Squids?) evolved vision along a different evolutionary path than our own. Also, as you pointed out, flys vision works differently than ours.
Evolutionary biologist, Ernst Mayr, wrote that the eye has evolved independently at least 40 different times on our planet. He said:
Since the eye seems to be fairly ubiquitous on Earth, it stands to reason that it would be with alien lifeforms, as well (assuming that alien lifeforms exist).
I’ve never seen a list, so I can’t answer your second question. I don’t know where Mayr came up with 40…