The AF18-250mm F/3.5-6.3 Di-II LD Aspherical (IF) Macro is the ultimate high power zoom lens boasting the world’s greatest zoom ratio1 of 13.9X. Tamron, the pioneer of high power zoom lenses, has achieved this milestone by commanding its technologies to further expand the capabilities of high power zoom lenses.
1As of September 2006. Based upon Tamron’s research of lenses for exclusive use with digital SLRs equipped with APS-C sized image sensors.
13.9X, the Largest Zoom Power in the High Power Zoom Class, Covering an Easy-to-use 28mm Wideangle to 388mm Ultra Telephoto (when converted to 35mm)
Tamron’s concept for the development of high power zoom lenses is “one-does-it-all, covering wideangle to telephoto” to satisfy customer needs for simplicity. Tamron has always kept this concept in mind when designing higher power zoom ranges. The question, “to what extent can the tele-end of a zoom starting with 18mm wideangle be extended in a lens designed for exclusive use with digital SLRs?” was posed and answered with the development of this ultra high power zoom lens possessing the world’s largest zoom ratio of 13.9X. It is not too long ago that the world of “wideangle to ultra telephoto film photography” could only be achieved with a combination of two zoom lenses; 28-200mm + 200-400mm2. Now, the world of digital SLR photography can be enjoyed with just a single zoom lens!
2 Circa 2000—A combination of 28-200mm and 200-400mm
Advanced Optical Design Aimed at Optimum Power Distribution to Achieve Compactness and High Power
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.
In order to realize the remarkable 13.9X zoom ratio, Tamron has pursued the approach to accomplish the compactness through optimization of the overall optical system, not through the employment of XR glass elements.
Revolutionary Minimum Focusing Distance of 0.45m (17.7”) throughout the Entire Zoom Range Affords a 1:3.5 Macro Capability
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.3
3Since the APS-C sized imager is smaller than the 35mm format film, the new zoom lens can fill the frame with almost the same scope (approx. 8 x 5.5cm) as a lens with a maximum magnification ratio of 1:2.3 on a 35mm film SLR camera.
Optical Design Dedicated for Digital SLR Photography by Optimizing the Angle of Incidence of Light Rays Reaching the Image Sensor
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.
Since the lens is designed exclusively for digital SLR photography, it provides high image quality resolution, contrast and flatness of image field.
Internal Surface Coating to Reduce Ghosting and Flare
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.
Ultra High Zoom Power, yet Lightweight and Compact Design Thanks to New Mechanical Devices
Complicated mechanisms are built into the compact body, thanks to new mechanical devices, for excellent portability and ease of use. Based on the mechanical construction of the AF28-300mm (Model A061), Tamron has revolutionized accumulated mechanical design technologies by reviewing the roles respective barrel parts play in order to achieve the high power, compactness and light weight. Additionally, the production engineering has been completely overhauled to downsize its parts and to increase their precision and durability in order to accommodate the complex structure in the new zoom lens.4
4In order to realize the 13.9X high zoom power, the lens uses a metal mount in all fittings.
Zoom Lock Mechanism Incorporated
The zoom lock prevents unwanted barrel extension when carrying the lens/camera combination.
Flower-shaped Lens Hood
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.
New External Design of the New Di-II Series Conveys the Image of “High Performance, High Precision”
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.