Yes, you are absolutely correct. To at least some extent, this aperature
effect makes brighter stars appear larger on the sensor. This diffraction
phenomina I described is real and can produce a similar effect often seen in
backlit photos and sometimes described as a halo. Bright light diffracting
through backlit hair can produce this halo without observed halation.
Asrtophotographers are (or should be) familiar with the phenomenon as it
also produces the star cross pattern from diffraction caused by the angled
mirror supports. As I understand it, a halo is often a reference to a glow
around a person or object and relates to representations as seen in
renaissance paintings, i.e., the references to a halo in other art forms, do
not refer to halation. Halation is a phenomena specific to photography,
though the word is derived from "halo" - [Origin: 1855-60; hal(o) + -ation].
Halo would then be generic to what is observed or depicted?
Regards,
Bob...
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From: "karl shah-jenner" <shahjen@xxxxxxxxxxxx>
: 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.
you're describing an Airy disk pattern of diffraction, not a halo or
halation
http://hyperphysics.phy-astr.gsu.edu/hbase/phyopt/cirapp2.html
and a nice explanation:
http://www.oldham-optical.co.uk/Airy%20Disk.htm
all sensors will record this, paper just recorded it slowly in your
experiment as the paper is slow
k
