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Lens review

Tamron SP AF 17-50 mm f/2.8 XR Di II LD Aspherical (IF)

27 September 2007
Robert Olech

3. Build quality

The Tamron 17-50 mm f/2.8 looks similar to the well-known 28-75 mm model. There is nothing strange about it since the two lenses can substitute for each other. One is designed for so called "crop" operations, while the other is designed for more common 35 mm frame operations. The tested lens is designed very well and has a solid build. The designers used a metal bayonet and the zooming takes place inside the lens body, which is good news for all polarization and graduated neutral density filter users. Additionally, the Tamron is equipped with a comfortable and quite precise manual sharpness adjustment ring (although it could have been a bit wider).

Tamron SP AF 17-50 mm f/2.8 XR Di II LD Aspherical (IF) - Build quality


As far as the overall parameters are concerned, the Tamron, in addition to its very good aperture (f/2.8), offers a sharpness minimum distance of 27 centimeters, no matter what focal length we use. We also get a seven-blade diaphragm, which could be stopped down to f/32.

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The inner construction of the lens looks very good as well. Despite having a somewhat limited focal length range, the Tamron’s construction is quite complicated with its 16 lenses set up in 13 groups. The most important thing is that the Tamron designers used lots of special glass. The first three elements are made of Extra Refractive (XR) glass, which bends the light strongly. This feature allows the lens size to be significantly smaller than its competitors. The strong light bending is, however, responsible for the presence of a somewhat significant chromatic aberration, so the designers had to remedy this in the next stage of production. They used low dispersion glass (LD). To combat the spherical aberration the designers used two aspherical elements. In the case of the Tamron 28-75 mm the proportion between the elements were a bit different since we had two XR lenses, three LD lenses and as many as four aspherical lenses.

Tamron SP AF 17-50 mm f/2.8 XR Di II LD Aspherical (IF) - Build quality


The comparison between the Tamron and the Canon EF-S 18-55 mm kit lens is presented in the picture below. It is worth adding that the 17-50 mm lens is smaller and lighter than the 28-75 mm.

Tamron SP AF 17-50 mm f/2.8 XR Di II LD Aspherical (IF) - Build quality