Ah yes,
I had forgotten the physics experiment of years ago in which we made
a difraction image using a point ( well almost ) source and an
intervening object.
With sufficient exposure time on photo paper ( I think the time was
about 10 minutes ) one obtained a shadow image of the object
surrounded by 'halo' rings of diminishing intensity as you have
described. So a sufficiently sensitive sensor could image such
'halos' and record them.
Nice that you pointed that out.
Cheers,
James
At 09:39 AM 12/30/2007 -0800, you wrote:
One of the natural sources...
Another source... Consider a distant point light source, for
example, a star. When it passes through a fixed aperture, the light
is defracted. What is actually passed to the film or sensor through
a perfect lens is no longer a parallel rays of light focused to a
point without dimentions. Rather, it's the light rays diffracted and
spread to form a circular pattern. The intensity decreases from the
center out. For mathematicians who may be curious, the intensitiy
follows a second order bessel function. For non mathematicians, the
function appears similar to a sine(x)/x curve. Anyway, as the
intensity of the source light increases, more of the tail of the
function (extending out the radius from the center) becomes visible
and the bright object (say, a star) becomes "larger". Eventualy, the
lobes of the function become visible as rings or halos of
diminishing intensity around the central point.
Extending this, every single point of the image is actually made up
of these patterns - overlapped. Further, the difraction does not
just take place at the aperture but also outside the camera in fron
of the lens. A highly backlit subject will also show this, such as a
bright light behind a subject with the "halo" around it's edges -
perhaps your model's head.
Regards,
Bob
James Schenken
