In article <4tj8vg$mle@csd5b.erim.org>, stahl@erim.org says...

>It is also worth noting that the resolution and sesitivity of the eye is
>not evenly distributed across the visual field. The center (most
>attended to area)also known as the fovea is more densly packed with
>cones (daylight, color receptors) that the rest of the retina. Outside
>the fovea are both Rods (larger, sensitive to lower light levels, less
>sensitive to color) and cones (less concentrated than atthe center).
>It is as if you had a fine grain color film at the ceter and a very
>fast but grainy (low color saturated to almost B&W) film arround the
>outside. The difference is usually noticeable at dusk. As the light
>fades you can see better by looking off center at things because of the
>greater low light performance of the rods arround the periphery compared
>to the cones at the fovea. I was actually trained to do this as a
>forward observed in the field artillery.

Yes, like having a super-wide-angle, super-wide-range zoom (8mm fisheye to 5000mm super telephoto equivalent for 35mm film), which is only reasonably good from maybe 100mm to 1000mm..... BTW, my peripheral vision is fairly
good, and I have learned to be able to place my attention spot somewhere
other than just the center, or to have a few attention spots simultaneously, or to attend to the whole field of view at once (I've heard that Navy plane spotters were trained to do that, also).
Hope This Helps