On 11-04-06 10:13 AM, Matthew Hunt wrote:
On Wed, Apr 6, 2011 at 10:06 AM, steve harley<p...@paper-ape.com> wrote:
interesting technique, and thanks for sharing, but it doesn't seem intuitive
that spherical aberration alone can describe soft focus
a thought experiment: if you aimed a soft-focus lens at just the right
concave surface, would everything be sharp? i think there'd still be more
going on
You're confusing spherical aberration with field curvature. Spherical
aberration is an on-axis aberration; it's what you get from a
spherical telescope mirror instead of a parabolic mirror. If you have
rays of light from a point source on axis (i.e. at field center), rays
of light at the edge of the mirror/lens come to a different focus than
rays that pass near the center. So even a single star at the center of
the field is blurred. It was the aberration that afflicted the Hubble
Space Telescope at launch.
And we think Pentax QA is bad. :-)
So how did they fix that? Send up a new mirror?
-bmw
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