Sharpens edges by reducing ‘colour fringing’
Chromatic aberration occurs when a lens element refracts different wavelengths of a ray of light – its rainbow colours – at very slightly different angles. This results in the ‘colour fringing’ that reduces the sharpness of an image. LD elements are made from special glass materials with extremely low dispersion indices (i.e. the refraction of a ray of light into rainbow colours is extremely narrow). Thus they effectively compensate for chromatic aberration at the centre of the field (on axis), a particular problem at long focal lengths (the telephoto end of the zoom range), and for lateral chromatic aberration (toward the edges of the field) that often occurs at short (wideangle) focal lengths.
Although costly, LD glass materials result in clear, vivid image quality.
Controls the dispersion of specific wavelengths of light
AD glass is a special type of optical glass that is used to achieve more precise control of chromatic aberrations, thereby enhancing overall imaging performance. Glass of this type provides an abnormally large partial dispersion ratio (amount of diffraction) for light of specific wavelength ranges (colours) within the visible spectrum. By combining AD glass having these special characteristics with elements made of normal glass having different dispersion characteristics, it is possible to control the dispersion factors of a specific wavelength.
This enhanced level of control results much lower levels of on-axis (central) chromatic aberration for telephoto lenses (or zooms used at telephoto settings) and a significant reduction of lateral (peripheral) chromatic aberration for wide-angle lenses (or zooms used at wideangle settings).
Like LD glass, AD glass material is costly but provides clear, vivid image quality.
Far superior image quality – while reducing lens size and weight
Tamron uses several hybrid aspherical lens elements in its lenses bearing the Aspherical designation. The benefits are two-fold: first, their non-spherical shapes virtually eliminate spherical aberration and image distortion. Second, as one hybrid aspherical lens element can take the place of multiple elements without compromising performance, they allow the lens to be much more compact.
As a result, these innovative optics have played a crucial role in delivering uniformly high image quality across all apertures and focal lengths of extraordinarily compact ultra-zoom lenses.
Broad-Band Anti-Reflective coating
Cleaner, crisper images without flare or ghosting
BBAR (Broad-Band Anti-Reflection) coatings reduce the lens reflection and dispersion that cause ghosting and flare. The coatings enhance light transmission in both the short and long wavelength ranges, ensuring excellent performance in all photographic conditions. Additionally, internal surface coatings are applied to cemented surfaces of all lens elements to deliver sharp, high-contrast images and flawless colour reproduction.