Tamron AF 17-50mm f/2.8 XR Di II LD (Nikon)
The Tamron AF 17-50mm f/2.8 XR Di II LD Aspherical [IF] is one of the most attractive offers in the standard zoom lens market for APS-C DSLRs. We did already check it out in some other mounts but for the sake of interest we're having a look at the Sony version here as well. You may excuse that most of the existing articles have been copied here - after all there're only marginal differences compared to the Nikon variant. Tamron has categorized the 17-50mm as a SP (Super Performance) lens which is Tamron's professional grade product league similar to the Sony G lineup. As indicated by the Di II the lens provides a reduced image circle so it is only compatible to APS-C DSLR (tested on the Alpha 700). Its field-of-view is equivalent to ~25.5-75mm (1.5x crop) on full frame cameras. The lens may be a "pro spec f/2.8" lens but at a price of around 350¿/US$ the Tamron is almost a budget item.
The build quality is very decent but typical for most Tamron lenses there's a little too much plastic in there. Nonetheless it is still one of the better implementations in Tamron land. Both the zoom and focus control rings operate pretty smooth. Unfortunately the latter does rotate during AF operations which is a bit dated by now. As you can see in the product shot above the lens extends when zooming towards the long end of the zoom range and the supplied petal-shaped hood adds a little extra length on top. Thanks to internal focusing the front element does not rotate so using a polarizer remains easily possible.
The lens has no internal AF motor and relies on a slotted drive screw operated by the camera. However, due to a very short focus path (about 45 degrees) the the AF is very fast. The AF accuracy is reasonably good - at least on the Alpha 700. FWIW, the tested sample has been serviced by Tamron due to a centering defect.
Specifications
Optical construction 16 elements in 13 groups inc. 2 hybrid aspherical elements, 1 LD (Low Dispersion) glass element, 1 XR (Extra Refractive) element
Number of aperture blades 7 (rounded)
min. focus distance 0.27m (max. magnification ratio ~1:4.5)
Dimensions 82x74mm
Weight 434g
Filter size 67mm (non-rotating)
Hood supplied, petal-shaped
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