The Tamron SP AF 20-40mm f/2.7-3.5 Aspherical (IF) is a fast wide-angle zoom lens for popular 35mm AF SLR cameras
The lens belongs to the SP (Superior Performance) series, i.e. professional lens series with highest optical performance and durability. The lens came in two outwardly different modifications: 166 (1994-1999) and 266 (2000-2006). The internal element coating of the 266 lens has a green gleam, and that of the 166 lens has a violet-brown gleam. The 1st version has a distance scale window; the 2nd looks more respectable. Many prefer the quality and the feel of ring travel of the 1st lens. The lenses' hoods are not interchangeable.
As for its characteristics the lens is more preferable for group photography and photojournalism at close and mid ranges. Abroad the lens has met with recognition from wedding photographers. A slight barrel distortion at wide angle. The lens can be used for landscape and architecture photography with a focus on a medium shot. Zooming at infinity is a bit poor. When taking close-up photos at narrow angle, the lens produces a very pleasant, somewhat watercolor bokeh. Color rendering is quiet, typical of portrait lenses. The picture is light and airy. Chromatic aberrations are absent at the center, though they are slightly visible towards the frame borders at extreme wide angle when wide open.
In the mid 90's a photo magazine published an article covering the test results of this lens. The lens showed a high resolution of 80 high-contrast lpmm at the center and 40 lpmm across the frame field at all focal lengths from the maximum aperture onwards. Some sources report two aspherical elements, one of which is a large diameter (42.5 mm) hybrid, and the other is in the rear group. The lens is also remarkable for its compact size and but at the same time presentable appearance on any camera.
Frame diameter: 62.5 mm
Back focal distance: 50.14 mm
Plain attachments diameter: 60.64 mm
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Posted by: Averin Date of publication: 23.03.2013