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

[afirkin at afirkin.com (afirkin at afirkin.com)]

Its the potential to cause problems with the photographic image and esp.
now with digital sensors which interests me. Not that many of my lenes
will stop down below f16/ f22 and mostly I'll use f8 or wider, but with
the creek shots etc I was using f22 to increase exposure. Perhaps I'd be
better with some ND filters.

Cheers

Alastair

> 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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>
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