From the Manufacturer
Tamron's original development of proprietary core technologies such as Aspherical element production, Multiple Cam Mechanism and Integrated Focus Cam design lend to the creation of the world's lightest, most compact 11x zoom lens made for digital SLR cameras.
AF18-200mm F/3.5-6.3 XR Di II Highlights Di II
|Zoom in for a macro shot |
Lenses are designed for exclusive use on digital cameras with smaller-size imagers and inherit all of the benefits of our Di products. These lenses are not designed for conventional cameras and digital cameras with image sensors larger than 24mm x 16mm. Extra Refractive Index Glass (XR)
|Special glass for better performance and more compact lens designs |
Extra Refractive Index (XR) glass can bend light rays at steeper angles, thereby decreasing the physical length of the lens while enhancing imaging performance by minimizing optical aberrations. This has allowed Tamron to develop a line of shorter, smaller-diameter, lighter lenses without sacrificing lens speed, and actually upgrading image quality compared to older designs. XR glass is costlier than conventional glass but it yields enhanced optical power distribution, making possible many of the outstanding and innovative lens designs that bear the XR designation. XR glass, with its superior light-bending power, makes it possible to design a short-barrel lens with the same light-gathering ability (aperture value) as a long-barrel lens—even with a smaller lens diameter. By using this principle Tamron has been able to shorten the length of the entire optical system and produce lighter, more compact lenses of the same speed, and also to provide greater zoom ranges in lenses that are much more convenient to carry by hand. Low Dispersion (LD)
Low dispersion (LD) glass elements in a lens help reduce chromatic aberration; the tendency of light of different colors to come to different points of focus at the image plane. Chromatic aberration reduces the sharpness of an image, but glass with an extremely lowdispersion index, has less of a tendency to separate (defract) a ray of light into a rainbow of colors. This characteristic allows the lens designer to effectively compensate for chromatic aberration at the center of the field (on axis), a particular problem at long focal lengths (the telephoto end of the zoom range), and for lateral chromatic aberration (towards the edges of the field) that often occurs at short focal lengths (the wide-angle end of the zoom range.)
Internal Focus (IF)
|Low Dispersion (LD) Glass for Greater Lens Sharpness |
Internal focusing (IF) provides numerous practical benefits to photographers including a non-rotating front filter ring that facilitates the positioning of polarizing and graduated filters, and more predictable handling because the lens length does not change during focusing. Even more important, Tamron’s Internal Focusing (IF) system provides a much closer minimum focusing distance (MFD) throughout its entire focusing range. In addition, IF improves optical performance by minimizing illumination loss at the corners of the image field, and helps to suppress other aberrations that become more troublesome at different focusing positions. Zoom Lock
Another original Tamron mechanical engineering concept is the Zoom Lock (ZL), a simple convenience feature that prevents undesired extension of the lens barrel when carrying the camera/lens unit on a neck strap.
The AF 18-200mm F/3.5-6.3 XR Di-II is a high power zoom lens made for exclusive use with digital SLR cameras. The lens inherits the qualities and concepts of the existing AF28-300mm F/3.5-6.3 XR Di. It covers a powerful zoom range that is the 35mm film camera equivalent to a 28-300mm* on a digital SLR camera with a APS-C size imager. The lens provides the convenience of handling many photographic scenes and the capability of shooting ultra wide-angle to ultra telephoto shots without changing lenses. Tamron uses three hybrid aspherical lens elements and two LD (Low Dispersion) glass elements to achieve effective compensation of on-axis and lateral chromatic aberrations, a critical factor that enhances the optical quality of digital photography. Systematic countermeasures against ghosting and flare, annoying factors in digital photography, are also adopted with new technologies such as "Internal Surface coatings" and new multiple-layered coating technology for ordinary elements. In addition, the Minimum Focus Distance is 45cm (17.7") so you will be able to enjoy close-up (macro) photography of 1:3.7 at a 200mm setting. Di II Lenses - Designed for exclusive use on digital cameras with smaller-size imagers and inherit all of the benefits of the Di products. These lenses are not designed for conventional cameras and digital cameras with image sensors larger than 24mm x 16mm. Key Features: Lightweight and Compact Design for Excellent Potability Flower-shaped Lens Hood Internal Surface Coating to Reduce Ghosting and Flare Dedicated for Digital SLR Cameras Optical System Uses Special Glass and is Optimized for Digital SLR Characteristics in order to Enhance Optical Quality in a Compact De