Designed for APS-C cameras but with a pro-spec build quality, this sub-£500 optic is a good update to an already popular lens
Tamron SP AF 17-50mm f/2.8 XR DI II LD Aspherical (IF) Review
Based on the previous, but still available, 17-50mm f/2.8 XR Di-II lens (which itself holds a WDC Gold Award), the new zoom incorporates Tamron’s three-coil vibration control technology. This has made the lens a little bit bigger but it remains remarkably compact and just heavy enough to suggest a solid build quality. The new lens also has an extra low-dispersion element and an extra aspherical profile for even better aberration control.
Less helpfully, and as was criticised when Tamron’s previous lens was reviewed, the IF mechanism does not disengage from the manual focusing ring in AF mode nor can manual focusing adjustments be applied. This means that fingers have to be kept clear of the focusing ring, which in turn makes it difficult to take a firm grip. For a lens that is otherwise so well-suited to low-light work, this is a notable weakness.
The vibration control mechanism is efficient, but I found it to have an odd jerkiness: this was apparent only on a tiny scale when trying to align the edge of the frame precisely against the edge of a wall, for example, but it was a little bit disconcerting. It is also slightly unnerving to feel the focusing ring so unrestrained in MF mode, given that the rearward zoom ring requires a definite effort to affect rotation. A zoom lock is provided to prevent accidental extension of the lens while it is being carried, but I doubt whether it is really needed.
Automatic focusing is reasonably quiet and an additional but very faint hum can be heard when the vibration control system is active. Both systems are brisk and effective. The focusing mode slider switch is set just above the similar VC switch on the left-hand side of the lens, within easy reach of the user’s left thumb.
The MTF graph peaks above 0.35 cycles-per-pixel but is weaker at full aperture, at minimum focal length and beyond f/22. Even so, across the most commonly used range of apertures Tamron’s new zoom puts in a strong performance. Better still, its pricing is surprisingly competitive for such a well specified lens.