read the Tamron and Tokina lens brochures. some of them are designated ELD.
Sigma uses SLD for super low dispersion. extra low dispersion means that the
different wavelengths of light are bent more uniformly across the spectrum
than plain optical glass, dispersion being when they are not bent uniformly
and end up acting more like a prism than an ideal optical element. this
leads to less chromatic aberration. a side effect of using much of this type
of glass is that it also has a higher refractive index and that means it
bends light more.
Herb....
----- Original Message -----
From: "mike wilson" <[EMAIL PROTECTED]>
To: <[email protected]>
Sent: Tuesday, April 05, 2005 3:38 PM
Subject: Re: Pentax's sudden infatuation with ED glass.
Indeed. If it was Extra low dispersion, then the initials would be ELD.
Manufacturers wouldn't miss the opportunity to stick _another_ letter into
a lens designation - except, maybe, Pentax.
