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

video guy - www.locoworks.com wrote: 
The focal plane is where the film is.  The place you describe is the
nodal point, where the rays of light cross within the lens.  But you do
not need a lens.  A thin piece of brass with a small hole drilled in it
and mounted in or over the lens opening of the camera body will serve.


Too small of a pinhole creates diffraction due to the "tunnelling"
effect.  As the diameter of the hole approaches the thickness of the
material, the hole becomes a tunnel and the light bounces off those
tunnel surfaces, softening the image.  If your material is thin enough
the image can be quite sharp, although you tend to get portholing (a
circular darkening around the edges of the image).  I made a pinhole
camera out of a view camera in photography school by punching a pinhole
in some black foil and taping it over the place where the lensboard was
attached.  The exposure time for Plus-X was several minutes in
sunlight.

This type of lens is also extremely wide-angle, which is a good thing
when photographing models.

Diffraction has nothing to do with 'tunneling'. Diffraction occurs when the pinhole is so small thet the light coming through it approaches being a 'point source' of light, and that light then radiates in ALL directions (as from a point), thus losing the very focus you had tried to obtain with the pinhole.

The functional principal of a pinhole depends on light traveling in straight lines ... once diffration starts to take over, due to a too small pinhole, that no longer holds.

Diffraction is due to light BENDING, not bouncing off 'tunnel' walls.

Dan Mitchell
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Relevant Pages

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