[rollei_list] Re: Contrast and Resolution
- From: "Eric Goldstein" <egoldste@xxxxxxxxx>
- To: rollei_list@xxxxxxxxxxxxx
- Date: Thu, 8 Nov 2007 20:38:36 -0500
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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