[rollei_list] Re: Contrast and Resolution

  • From: Choiliefan@xxxxxxx
  • To: rollei_list@xxxxxxxxxxxxx
  • Date: Thu, 8 Nov 2007 21:56:44 EST

 
In what ways, if any does refraction affect this as the lens is stopped down?
This distribution of energy must give individual lenses their signature bokeh 
then, no?
I'm trying to get a grasp on this...
Health, Peace
Lance
Selma, NC 27576
~~~~~~~~~~~~~~~~~~~~~~~
In a message dated 11/8/2007 8:40:22 PM Eastern Standard Time, 
egoldste@xxxxxxxxx writes:

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.
---
Rollei List





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