Diffraction is based on focal ratio, not simply focal length or physical
size of the aperture. Diffraction in a lens is caused by light rays
bending around the edges of the lens retaining cells and especially the
blades of the diaphragm. The larger the focal ratio the greater
relative distance the beams have to travel after passing the diaphragm
blades and the greater the linear displacement from where they're
supposed to land on film or sensor. The smaller the size of the pixel
the greater the chance that the wayward beam will fall outside the pixel
position it was intended for. The same happens with film, of course,
except no one paid attention then.
Chuck Norcutt
Ken Norton wrote:
>> Thanks for Wayne and Chuck's confirmation, then we may only be able to
>> shoot
>> at F4 with the 7-14 at 7mm :-) I would prefer to use my 16mm fisheye with
>> OM5D II.
>
>
>
> Sorry, at 7mm, the lens is diffraction limited at F1.4 according to the
> calculations.
>
> ;)
>
> AG
--
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