Sigma Switches to FLD Glass in New Lenses
New lenses coming out of Sigma will be a little bit different than the company's other offerings. All of their new high end lenses will be switching from traditional glass to new F Low Dispersion (FLD) glass. It's got the same performance as fluorite glass but it's much cheaper.
FLD glass is the top tier of low dispersion glass. It's got extremely high light transmission and a low refractive index when compared with traditional optical glass. FLD also benefits from excellent correction for residual chromatic aberration, which can't be done by optical glass.
Four elements of FLD glass have been included in the Sigma 8-16mm F4.5-5.6 DC HSM, while two elements have been introduced to Sigma's APO 70-200mm F2.8 EX DG OS HSM and the Sigma 17-50mm F2.8 EX DC OS HSM.