> > these extreme apertures, coma, vignetting and other optical
>
> coma ? as in, oh my god, how expensive is this lens *faint* or as in when it
> falls on your head ?
> :-)
>From the Canon Lens Work book (just in case you didn't know):
Coma, comatic aberration
Coma, or comatic aberration, is a phenomenon visible in the
periphery of an image produced by a lens which has been
corrected for spherical aberration, and causes light rays
entering the edge of the lens at an angle to converge in the
form of a comet instead of the desired point, hence the name.
The comet shape is oriented radially with the tail pointing
either toward or away from the center of the image. The
resulting blur near the edges of the image is called comatic
flare.
...
The elimination of both spherical aberration and coma for a
subject at a certain shooting distance is called aplanatism,
and a lens corrected as such is called aplanat.
Lars
--
Lars Michael [EMAIL PROTECTED]
87GT http://www.larsmichael.com/
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