You also have to bear in mind that the human eye is only good for one
arc minuet in ideal conditions. that means you will struggle to see
anything smaller than 3cm at a range of 100m.
At 10km you will struggle to see a 3m white object against a black
background. That's not good if you want to see a grey mast against
a hazy blue background from a moving boat, even if it is not obscured
against the curvature of the earth.
__________________
|