Diffraction and macro

[P3D Dylan The Hippy Wabbit <spacey@xxxxxxxxxxxxx>]

Hi,

Josh asked:-

>If diffraction is caused by edges, what if the aperture were a small
>circular gradient on a transparent film where the diaphragm would
>otherwise be, instead of a sharply-defined hole?  Then there wouldn't be
>an edge per se.  Would that eliminate or minimize the diffraction?

Wouldn't it also minimise the benefit in terms of depth of field?  The
circle of confusion would have fuzzy edges, making it larger as if you had
used a bigger aperture.  My *guess* is that the diffraction and depth of
field would both resemble what you'd get at an aperture of the average
size of your diffuse hole.

I suspect that the dangers of diffraction are overstated in any case.
Diffraction is most significant when the aperture is of the same order of
magnitude as the wavelength.  Since we measure apertures in mm rather than
*angstroms* I wouldn't worry.

Dave Spacey


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When you break rules break 'em good and hard.   - Terry Pratchett


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