I've searched a bit in google about the vision of the common housefly but most studies are on the drosophilia. First, am I right thinking that they see in 2 dimensions rather than 3? Because to see in 3 dimensions would require a somehow large distance between the extremum of their "eyes" and it's actually quite small compared to the separation between human eyes. Second, I read that their vision is actually excellent in term of speed and precision. I guess that's basically why a fly can follow without any problem another fly that is zigzaging extremely fast for us. And apparently they can see the edges of objects really accurately, they have an extremely high resolution (can see better than a 1 mm thick object even 2 meters away from it http://phys.org/news129545593.html). However I discovered by myself that I can actually approach a fly and even touch it without it seeing me. I would like to know what in their vision is failling in the following "test", or "set up": let's say you are at about 40 cm away from a fly resting over a table. Point toward the fly with your index finger and go toward the fly slowly. It won't see it. You can go really close to it, and if you don't mind having a dirty finger you could just press the fly against the table. Obviously the fly doesn't see your finger getting bigger and bigger. Or should I say closer and closer. I have read nothing about this... So it doesn't seem a well known fact? I've tested this on many flies since I'm around 10 years of age. So if they have such an amazing vision, how come they can't see a finger coming slowly to them? I should mention that if you don't go toward the fly with your finger in a straight line, the fly will see you and get away as soon as you deviate from a straight line.