Sigma 12-24mm, Tamron 10-24mm & Verdict

Sigma 12-24mm EX DG HSM

Street price (October 2009): £700

EISA gave the Sigma 12-24mm EX DG HSM lens its European Lens of the Year Award for 2004-5 on account of the zoom's impressive 12mm minimum focal length and compatibility with both full-frame and APS-C cameras.

Being a full-frame zoom the Sigma 12-24mm EX DG HSM is larger than its APS-C (DC) stable-mate: further bulk comes from the non-removable petal-shaped lens hood, which needs an adapter-collar to be slid over it before the lens cap can be fitted. This is a rather inconvenient arrangement and it is not clear why Sigma hasn't simply supplied a bespoke slip-on lens cap. It is true that the lens cap and adapter can be slipped-off as a single item but they then tend to separate. If I owned this lens I would be tempted to glue the lens cap onto the adapter!

The fixed lens hood also means that filters cannot be fitted to the front of the lens so Sigma has helpfully provided a gelatine slot at the rear. Users who are not accustomed to fitting gelatins may find this solution rather awkward and should move the lens to its 24mm setting to avoid touching the rear element. Regardless of dexterity, polarising filters are out of the question since they cannot be rotated.

These niggles aside, Sigma's 12-24mm full-frame handles very well. The forward manual-focusing ring is available at all times in AF mode (on Canon, Nikon and Sigma cameras) and is nicely geared for accurate use. The rearward zoom ring requires a slight shift of grip but again has a very pleasing feel.

Automatic focusing is carried out internally so there is no need to keep fingers clear of the focusing ring. A distance window is provided together with depth-of-field markings for both maximum and minimum focal-length settings should they be needed.

Although it is not evident from the resolution curves, there is some colour fringing at the 12mm setting but the effect is slight and is likely to go unnoticed in most situations.

Overall, full-frame users will enjoy the Sigma 12-24mm EX DG HSM, but APS-C cameras are better served by its DC sibling, which offers better performance at a lower price.

Tamron SP AF10-24mm Di II LD IF

Street price (October 2009): £420

Whereas most zooms in the ultra-wide category settle for a 2x zoom range, Tamron has managed to achieve 2.4x with no price penalty. Tamron has also got its ergonomics just right - the less commonly used manual focusing ring is significantly narrower than the more important zoom ring and is also placed very much towards the front of the lens.

This is important because Tamron's lens does not have internal focusing so fingers must be kept clear of the focusing ring when AF is set. Fortunately this is easy to ensure. Equally importantly, the focusing ring has a silky-smooth feel when the lens is set to MF mode - a feel that is also echoed by the wider and more frequently used zoom ring.

With so much to like about the design of the Tamron SP AF10-24mm Di II LD IF it is a shame that, even when simply looking through the viewfinder and doing a visual comparison with other lenses, the Tamron appeared to lack real bite. Technical testing revealed significant levels of chromatic aberration and overall softness, but real-world use showed that these potential problems are remarkably unobtrusive in most images although there were times when corner softness became evident as soon as it was sought.

The degree of mismatch seen in its MTF curves (above) suggests that this lens might be a rogue samples (as has appeared in some previous WDC lens tests). Encouragingly, however, at its most demanding (minimum) focal-length setting the Tamron 10-24mm achieves around 0.3 cycles-per-pixel. If this very laudable performance is representative of what a better sample could achieve throughout its zoom range then Tamron's lens should be every bit as good as its peers.

Overall, so much about Tamron's zoom is right and the basic design looks sound. The performance lapses noted here are likely to be isolated. For prudent buyers it would seem to be a sufficient precaution (as should be done with any lens purchase) to do a few test exposures in the store and then to examine them at high magnification before parting with funds on behalf of a specific item.