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LD-Hybrid Aspherical/AD-Hybrid Aspherical Elements
The use of LD and AD glass permits Tamron lenses to provide unparalleled optical quality while eliminating chromatic aberrations that can denigrate image contrast and sharpness.
However, the mass-production of a high-performance lens, as revolutionary as the Tamron AF28-300mm (where AD-Hybrid is used) or SP AF28-105/2.8 (where LD-Hybrid is used), required that Tamron's engineers develop new methods of lens manufacturing. The material characteristics of the optical resin, which requires an optimized temperature during the molding process, and the fragile physical nature of LD glass during the polishing and coating process, all but prevented their use in tandem until Tamron devised a method by which a specially-treated aspherical layer could be adhered to the finished LD or AD glass element that would ensure perfect bonding of the two elements. By precisely monitoring temperature control during the production process two different types of lens elements are made into one enabling the Tamron AF28-300mm ad SP AF28-105/2.8 to provide image quality that other lenses simply cannot approach. (Models A06 and AF76)
Model A06 Optical Construction
Hybrid Aspherical Elements Provide the Ultimate in Compactness and Image Quality
By using the latest advances in technology, spherical aberration and image distortion, often prevalent in high zoom ratio lenses, have been eliminated in Tamron's high-power zoom lens series. Through application of Tamron's exclusive Hybrid Aspherical technology, (which can take the place of multiple optical elements) to LD glass, a never-before-possible level of image quality and compactness has been attained. Weighing a mere 20.6oz (585g)*, with a retracted length of 3.7" (93.6mm)* and a maximum barrel diameter of 3.2" (80.4mm)*, the Tamron AF28-300mm gives you the freedom to break the gravitational pull of uncreative photography. *Values for Nikon AF mount.
Compensation effect with an aspherical lens element
Special Glass Materials Employed for High Image Quality - LD (Low Dispersion) and AD (Anomalous Dispersion) Lenses
In order to reduce and eliminate secondary (residual) chromatic aberration that cannot be removed by conventional optical glass, we have actively incorporated special, highly effective LD (Low Dispersion) and AD (Anomalous Dispersion) glass materials. These costly glass materials result in clear, vivid image quality.
About LD (Low Dispersion) Lens Elements
Chromatic aberration is a form of optical noise that reduces the sharpness of an image. LD elements are made from special glass materials with extremely low dispersion indices (characteristics that separate or refract a ray of light into rainbow colors) that effectively compensate for chromatic aberration that is particularly a problem at the telephoto end. (Model 371/471D, Model 185/285D)
The difference in chromatic aberration (dispersion characteristics) between normal optical glass and LD glass elements
About AD (Anomalous Dispersion) Lens Elements
Anomalous Dispersion glass is a special optical glass that delivers an abnormally large partial dispersion ratio (amount of dispersion at a given wavelength range within visible light) relative to a specific wavelength zone. By combining AD glass elements with elements made of normal glass with different dispersion characteristics, dispersion factors of a specific wavelength can be controlled, resulting in effective compensation of on-axis chromatic aberration on telephoto lenses, or lateral chromatic aberration often associated with wideangle lenses of conventional optical configuration. (Model 190D)
The difference in partial dispersion factors between normal optical glass and AD glass elements