There used to be illustrations of this on the web but I am not finding
them now. Essentially, a lens can either be designed to draw the
energy of the point as distributed as a concentrated central point
with a light, airy disc of lesser energy surrounding it, or a light
airy central disc with a more concentrated ring of energy surrounding
it on the periphery. One yields higher resolution, the other higher
edge contrast/accutance...
But the notion is that it is the distribution of energy around how the
lens draws a point of light which accounts for the difference...
Eric Goldstein
--
On 11/8/07, Richard Knoppow <dickburk@xxxxxxxxxxxxx> wrote: (snipped)
If one charts the energy distribution of a beam of
light focused by the lens one finds that the high contrast
lens concentrates the light in a small beam or spot but has
many smaller peaks or beams surrounding the main beam. These
cause a sort of flare around the main beam lowering the
contrast. By suitable adjustment these secondary beams can
be much reduced at the cost of making the main beam broader.
The second condition reduces the resolution but increases
the contrast. The process is known as apodisation or removal
of the feet. For those familiar with radio antennas or
acoustic radiators an exactly analagous condition exists
there, the suppression of minor lobes with the concurrent
broadening of the main lobe.
---
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