In its new AF18-250mm f/3.5-6.3 Di II LD Aspherical [IF] Macro lens, Tamron has provided an impressive 13.9x zoom magnification yet only added 0.2 mm in diameter and 0.6 mm in overall length to the dimensions of the AF18-200mm Di-II lens. Designed specifically for DSLR cameras with 'APS-C' sized image sensors, this lens covers the equivalent of 27-375mm on Nikon, Pentax and Sony camera bodies and 28.8-400mm on a Canon DSLR. We tested the lens on the new Nikon D60, which lacks a built-in focus drive motor and, therefore, relies on the AF motor in the lens for all autofocusing.
The optical system in the new lens consists of 16 elements in13 groups with an LD (Low Dispersion) glass element and one AD (Anomalous Dispersion) lens in the first group to minimise on-axis chromatic aberration, particularly at long focal lengths. Two hybrid aspherical lens elements have been used to provide a compact optical design and the third lens group has been optically configured to minimise astigmatism while maintaining high zoom power and optimal image quality.
The optical design is also digitally-orientated with the aim of providing angles of incidence that ensure optimal light levels reach the imager over the entire image field throughout the zoom range. High image quality and resolution, adequate contrast and flatness of image field have been primary goals. Multiple-layer coatings on cemented surfaces of plural elements and ordinary elements ensure 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 minimum focusing distance of 45 cm is maintained throughout the entire zoom range, providing a maximum magnification ratio of 1:3.5 at the 250mm end of the zoom range. It's not true macro but it does provide some great close-up pictures. Internal focusing makes it easy to use angle-critical filters with this lens. A metal lens mount is provided and a flower-shaped lens hood is included as a standard accessory.
The lens barrel is solidly designed and very compact for the focal length range this lens covers. A broad zoom ring is located towards the camera mount, while a narrow focus ring is situated near the lens hood mounting. Both rings are quite heavily textured to provide a very secure and comfortable grip. The gold ring that characterises the Tamron brand is located between them.
Margaret Brown
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