[Leica] Does anyone have a simple way to explain this

[jsmith342 at gmail.com (Jeffery Smith)]

Diffraction occurs on the edge of the iris diaphragm. Because the diameter 
of the aperture opening is determined by 2?r but the area of the aperture is 
determined by ?r?, the greater the radius, the greater the area:diameter 
ratio. Thus, the smaller the radius of the aperture, the greater the impact 
of diffraction. The shorter the wavelength, the less the diffraction, but it 
isn't much of a factor until you get to 1,000-power on a microscope.


On Nov 27, 2010, at 6:11 PM, afirkin at afirkin.com wrote:

> Diffraction Limits:
> 
> The diffraction limit is dependent on the wavelength of the light and the
> f-stop.   It is calculated as the size of an Airy disk (Sir George Airy). 
> This describes the size of a circle from a point of light as it passes
> the edges of the aperture.   Fundamentally, as you decrease the aperture
> size (increase the f-stop) the size of the Airy disks increases.   An Airy
> disk can also be called a blur circle at the image plane similar to the
> CoC for DOF.   The simplified calculation (estimation) is 1500 divided by
> the aperture.   Thus, f/8 yields .005 mm and f/64 yields .042 mm.   The
> relationship between the size of the Airy disk and resolution is known as
> the Rayleigh criteria.   Since it takes two of these points of light to
> define resolution the respective resolutions are 100 lp/mm for f/8 and 12
> lp/mm for f/64.   Obviously, stopping down the aperture to increase depth
> of field can lead to increased diffraction that blurs the entire image.
> 
> Most photographers would agree that 35mm cameras become diffraction
> limited at f/22.   At smaller aperture sizes diffraction trumps depth of
> field and the overall image loses resolution.   For a typical digital
> sensor size the diffraction limit is a factor at f/16.   Diffraction
> limits are less significant with medium and large format cameras.   This
> is only because there is less need for enlargement therefore the CoC
> values can be relaxed.
> 
> 
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