Review of the Tamron SP AF 17-50mm f/2.8 XR Di II IF Aspherical lens
Optical performance is very good. The lens peaks at over 0.35 cycles per pixel in the very useful f/5.6 to f/8 range and, right out to f/22, only drops below the crucial 0.25 figure at the extreme aperture settings of its minimum focal length. Unusually for a fast lens, the Tamron 17-50mm f/2.8 can be stopped right down to f/32 but at this stage the resolution is around 0.2 cycles per pixel, indicating that diffraction has kicked-in to a very significant degree.
The zoom action is just a little stiff and the minimum focusing distance is only 0.27m so, quite properly, there is no suggestion that this might be regarded as a ‘macro’ lens. Interestingly, the front element and filter-mounting ring are significantly smaller than those of Sigma’s equivalent lens, making the Tamron less bulky and, potentially, cheaper to buy filters for. There is slight pincushion distortion at the longest focal length but, despite its smaller diameter, the lens does not seem to have any less light-gathering power.
Despite being proclaimed as an IF lens, the forward-positioned focusing ring rotates while the lens focus is being adjusted and the instructions specifically warn that interfering with the focusing ring may cause serious damage. All of this is a shame because it really can be very difficult to avoid having your fingers resting on the focusing ring. Nevertheless, this is a very well specified and keenly priced lens that deserves serious consideration.
This test has proved that the low-cost label so often associated with independent lenses indicates only part of their appeal. Image quality and usability are also strengths and Tamron's 17-50mm f/2.8 also manages to be surprisingly compact. The Tamron is a nice lens all-round – it's just a shame that the focusing ring rotates in AF mode yet seems not to allow manual adjustment for those occasions when the camera fails to focus on the desired plane.