"Alan B. Pearce" wrote:
>
> >I'm not sure why this is, but if you stand facing a mirror and hold a
> >digital clock with the display facing the mirror (so you can see its
> >reflection) and move it around quickly, often you can see the individual
> >numbers broken apart.
>
> It does not need to be in a mirror. If you have a calculator or digital
> watch with LED display and wave it about in front of you while looking at a
> fixed point you can see this effect.
>
> Another effect that I have noticed is that a TV screen will show flicker
> when seen out the corner of your eye. Peripheral vision is much more
> sensitive to these effects, and does not have the "afterglow" effect of
> straight ahead vision. The other effect I have noticed is when there is an
> oscilloscope screen off centre of vision, it is sometimes possible to get
> the effect of the spot scan being stopped mid screen when you move your
> head. This is somewhat dependant on the scope scan speed and the direction
> of movement of your eyeball relative to the trace scan direction.
>


I was once testing a circuit that generated pulses at a slow rate. The
scope took a good fraction of a second to sweep across the CRT when
viewing the pulses. I noticed that the scope sweep was nonlinear -- the
pulses were bunched at one edge of the screen. I spent some time trying
to find what was funny about the scope.

It turned out that it was an illusion. My eyes fixed at the left side of
the screen waiting for the sweep to start and then took a while to catch
up with the slow sweep of the beam across the screen. This made the
pulses look closer together at the start of the sweep if I remember
correctly.


-- Rich



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