Tamron SP AF11-18mm F/4.5-5.6 Di-II LD Aspherical (IF)
The optical system uses one element each of HID (High Index/High Dispersion glass) and LD (Low Dispersion) glass to minimize on-axis and lateral chromatic aberrations that are the greatest hindrance to high optical quality. In addition, the lens uses a high-precision, large clear aperture, glass-molded aspherical element and two hybrid aspherical elements to thoroughly compensate for spherical and chromatic aberrations and distortion, in order to achieve outstanding optical quality.
The zoom lens also uses a new optical system designed to confine the changing angle of incidence of light rays reaching the imager within a certain scope over the entire image field from the center to the periphery, by considering the effects of variances due to zooming.
Ghosting and flare caused by aberrations are annoying factors in digital SLR
photography, so Tamron has adopted various countermeasures against the problem
including the employment of "Internal Surface Coatings" (i.e., multiple-layer
coatings on cemented surfaces of plural elements) and new multiple-layer coating
technology on ordinary elements in order to minimize reflections that occur
when light enters through the front element and to reduce image degrading effects
caused by the imagers themselves.