And while Sigma has itself recently announced a new constant maximum aperture 10-20mm F3.5 EX DC HSM, the indications are that this will sell alongside the slower model as a higher-priced premium product. In the Four Thirds mount, Olympus has also entered the arena with its very impressive Zuiko Digital ED 9-18mm F4-5.6. Of course the market doesn't stand still, and Tamron (arguably Sigma's biggest direct rival) has recently revised its own offering in this sector with the SP AF 10-24mm F3.5-4.5 Di-II LD Aspherical (IF). The 'DC' designation indicates that this lens is designed for DSLRs with APS-C or smaller sensors, and isn't suitable for use on a full-frame body (the image circle isn't large enough, and vignetting will occur).
Users of Canon, Nikon, Sigma, and Four Thirds cameras benefit from an ultrasonic-type 'HyperSonic Motor' (HSM) for fast and silent autofocus, while the Pentax and Sony mount versions use the 'screw-drive' coupling from the camera body. The optical formula features 14 elements in 10 groups, including three Super-low Dispersion glass elements for the minimization of chromatic aberrations, and three aspherical elements to reduce distortion and other aberrations. Equally it's not hurt by having a very competitive price it's notably much cheaper than the camera manufacturers' own offerings in this sector. It has since become a very popular lens, due in no small part to offering the joint-widest angle of view of all the APS-C ultra-wide zooms, while being available in mounts to fit all of the major DSLR systems. It was introduced amongst a flurry of announcements as manufacturers raced to provide wideangle zooms for the burgeoning APS-C format DSLR market, with similar offerings also appearing in short measure from the likes of Tamron and Tokina (not to mention all of the major camera companies). The 10-20mm F4-5.6 EX DC HSM is Sigma's offering in the APS-C ultrawide zoom sector, first announced in February 2005.
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