The term "apperations" is a portmanteau of the words "aberration" and
"apparition" used by lens designers to describe a highly specific and
little-understood quality of lenses made from certain rare-earth
glasses. The off-axis tangential coma can be corrected fully by the
use of a symmetrical design such as the Planar, but a residual amount
of barrel distortion towards the periphery of the image circle will
result, which causes a fundamental change in the bokeh of a lens as
one moves from the center to the edges. In effect, out-of-focus
points in the center will be rendered normally but OOF points of
light toward the edges take on a more diffuse, some say almost
"spiritual" quality. This phenomenon was studied by Kaspar Geist of
Zeiss in the 1930s, a shadowy figure himself in the annals of Zeiss
history, but his research came to a halt as his supply of rare-earth
glasses interrupted was interrupted during the war.
Among Zeiss lens designers, the term was also used ironically to
describe those whose jobs brought them into constant contact with
such lenses.
I hope this helps clear up any confusion.
Best regards, Aaron
On May 15, 2006, at 9:33 AM, Neil Gould wrote:
You use the term "apperations", above, that I have not seen and couldn't
find a definition, although the tangential references were intriguing.
Could you explain this term?
