SP 17-50mm F/2.8 XR Di-II VC LD Aspherical For Canon APS-C Digital SLR Cameras Black

The optical design of this lens uses a high-performance xld (extra low dispersion) element, which is manufactured out of a special glass with an extremely low refractive index
The refractive index describes the ability of the lens to split a light beam into its spectral colours
The dispersive properties are even lower than standard LD lenses and are at a level similar to fluorite
Xld lens in combination with the ld element delivers the highest contrast and brilliance
effectively prevents the problem of chromatic aberration in telephoto photography and delivers a high level of sharpness even in the peripheral regions