Camera Accessories

Tamron has tagged its new 17-50mm F2.8 lens with the 'SP' label, indicating Super Performance, which puts it into the professional product category. It also bears the Di II designation, indicating a second-generation, digitally integrated lens that is designed for use with 'APS-C sized' sensors and mounts are available for Canon, Nikon and Sony DSLRs. As tested on a Canon EOS 300D, it covers a field of view equivalent to approximately 27-80mm.

Optically this lens consists of 16 elements - including two hybrid aspherical elements, one LD (Low Dispersion) glass element and one XR (Extra Refractive) element - arranged in 13 groups. The f2.8 maximum aperture is maintained throughout the zoom range. The lens focuses internally by moving groups of elements within the barrel. Consequently, users can fit angle-sensitive polarising and graduated filters without having to re-set them whenever the focus or focal length is changed.

The focus mechanism on the test lens was fast and accurate in normal lighting but showed slight hesitancy in low light. However it was relatively noisy when compared to other lenses we've tested. A zoom lock is provided to prevent the lens barrel extending when the lens is fitted to a camera and carried pointing downwards.

For close-ups, this lens offers a maximum magnification ratio of 1:4.5 with the 50mm setting when it is focused on subjects 27cm from the camera - the closest focusing distance throughout the zoom range. It's not true macro but it's good enough for taking close-ups of larger flowers and artworks. For normal shooting, images were generally sharp and flare seemed well controlled in backlit situations as long as the sun was well out of the frame and the supplied lens hood was fitted.

We noticed a slight increase in image contrast when stopping down from f2.8 to f4, even for normal shots. However the effect is barely discernible in normal photography. Noticeable barrel distortion was observed at 17mm but this evened out at 24mm and was absent by the 35mm position. In addition, some pincushioning was discernible at 50mm.

Vignetting (corner darkening) was quite obvious at maximum aperture at 17mm but the effect vanished by f5.6. This vignetting progressively disappeared with increasing focal length and was absent by 35mm. We feel this vignetting would be a very minor problem in normal usage as most photographers will prefer to shoot at smaller apertures where its effect is minimal.

No vignetting at 35mm

Imatest testing revealed a detectable level of lateral chromatic aberration, which was most significant at 17mm. However, overall it was relatively low and we feel most photographers would not notice it in general photography. At longer focal lengths you'd need to look hard - or enlarge shots substantially - before you would observe any problems. Overall edge-to-edge sharpness and image resolution were also pretty good, with the best results from Imatest testing coming at 24mm with apertures of f4 to f8.

So, what's missing? Image stabilisation is popular in zoom lenses, although it's more of a 'nice to have' feature than a necessity in wide zooms and this Tamron lens doesn't have it. Otherwise, all the functionality photographers want is provided in a relatively compact, solidly-constructed package. The rubberised zoom rings are comfortable to handle and the lens zooms smoothly between its widest and narrowest positions.

Since this lens covers the same focal length range as the lenses supplied with most entry-level DSLR cameras many potential purchasers will need to consider whether it's worth spending over $700 on a lens that is heavier than many kit lenses and offers few benefits in terms of image resolution and colour reproduction. However, the Tamron 17-50mm lens is between half a stop (at 17mm) and two stops (at 50mm) faster than any of the kit lenses.

If you enjoy low-light photography or require a fast lens that can blur backgrounds and stop action, this speed advantage would be worth paying for and you could be well served by the Tamron SP AF17-50mm F/2.8 XR Di-II LD Aspherical [IF] lens. If you're buying a DSLR body on its own, this lens covers a useful focal length range and its more rugged construction would make it a good choice as a standard zoom to match the camera body - but only if the camera has an 'APS-C sized' sensor.

IMATEST RESULTS


Lateral chromatic aberration was lower at 35mm (lower graph) than at 17mm (top graph) but relatively low across the focal length range.

Best resolution was obtained mid-way along the zoom range at apertures around f8 (lower graph).

SAMPLE IMAGES

Close-up.

17mm focal length (= 27mm in 35mm format).

50mm focal length (= 80mm  in 35mm format).

Focal length range: 17-50mm

Maximum aperture: f2.8 throughout the zoom range

Lens construction: 16 elements in 13 groups

Minimum focus: 0.27m throughout the zoom range

Filter size:  67mm diameter

Dimensions (Diameter x L): 73.8 mm x 83.2mm                

Weight: 430g