Tamron AF18-250mm Di II With Built-In Motor For Nikon Mount
By Shutterbug Staff January 17, 2008 — Tamron has announced the AF18-250mm F/3.5-6.3 Di-II LD Aspherical (IF) Macro, a lightweight, compact and ultra high power zoom lens designed exclusively for digital SLR cameras with APS-C sized image sensors with a Built-In Motor for Nikon (Model A18N II). The AF18-250mm F/3.5-6.3 Di-II LD Aspherical (IF) Macro boasts the world’s greatest zoom ratio of 13.9X.

The optical system uses an LD (Low Dispersion) glass element and one AD (Anomalous Dispersion) lens in the first group to minimize on-axis chromatic aberration while achieving the 250mm ultra-tele focal length. In addition, suitable positioning of two hybrid aspherical lens elements serves to meet the desired compactness despite its 13.9X zoom power. In particular, Tamron’s engineers have pursued a thorough analysis of the optical configuration of the third lens group for optimum power distribution in the overall optical system. The approach has resulted in the sufficient compensation of aberrations, including astigmatism; the compactness, thanks to downsizing of the first group; the high zoom power; and optimum optical quality.

The new zoom lens achieves a minimum focus distance of 0.45m (17.7”) throughout the entire zoom range, top of the class capability among high power zoom lenses for digital SLR cameras, which results in a maximum magnification ratio of 1:3.5 at the 250mm tele-end.

The zoom lens uses an optical system designed to confine the changing angles of incidence of light rays reaching the imager within a certain scope over the entire image field by considering the effects of variance due to zooming.

Through the use of "Internal Surface Coatings" (i.e., multiple-layer coatings on cemented surfaces of plural elements) and new multiple-layer coating technology on ordinary elements, ghosting and flare due to reflections that occur when light enters through the front element and reflections caused by the imager itself are reduced to the absolute minimum.

A flower-shaped lens hood is included as a standard accessory. The special hood provides optimum shading of superfluous light rays that enter from the rectangular frame outside the image field.

Improvements have been made to the external design by adding a gold-colored and between the focus and zoom rings to enhance the appearance and make the product stand out as a Di-II lens. Also, the black coating over the entire lens barrel creates a high-quality, sophisticated look. The focus and zoom rings use ergonomic rubber patterns to provide better handling and a design that complements the camera style.

www.tamron.com