Re: Digital cameras & depth of field (my experience)

video guy - www.locoworks.com wrote: 
Dan, light does not bend.  It reflects, it refracts, it diffuses, but
it does not bend, at least in this universe.  If you don't understand
that, you have no business trying to explain something as simple as a
pinhole.

If you don't think light bends, you've just flunked physics, and if it doesn't lots of optics devices would not work, and Einstein and several others would not be famous! You're still stuck in oversimplified and outdated 'ray' optics concepts. Like Newtonian mechanics, that only 'sort of' works, sometimes, in some situations. You have to think in terms of 'wave' optics, and wavefronts to begin to understand diffraction. Light is bent by diffraction, refraction, and gravity (at least).

And, the physics of pinholes is NOT simple.

The thickness of the material the pinhole is made from has nothing to do with diffraction, it occurs at the geometric face of the pinhole, even if it had NO thickness (which of course is physically impossible). Even pinholes in the thinnest materials create diffraction.

I can see that some form of the 'tunneling' you mention could also occur, but that's NOT diffraction. In physics one usually tries to get the thinnest possible material (metal foils) to make pinholes (or slits) in, to get the BEST (cleanest) possible diffraction, free of your so called 'tunneling' effects.

Actually ALL holes create diffraction, but only at their edges. For larger holes, most of the light passing through goes straight, and is not significantly diffracted. The small fraction that passes near the edge of the hole is diffracted just as for a pinhole, but it's a very small part of the total, and is largely 'lost' as unwanted noise. The effect is to sightly softens the "focus' of ANY light passing through ANY aperture (or past ANY edge). Which is to say, there are NO 'sharp' edged shadows.

When a 'pinhole' size is approached, most of the light passing through the hole begins to interact with the edges of the hole, and diffraction becomes a very significant part of the total transmission. Most of the light is diffracted, and hardly any passes straight through.

All this can be demonstrated analogously with a water 'ripple tank'.

Dan Mitchell
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Relevant Pages

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