Photozone, one of the web's most-trusted resources for SLE camera lens reviews, has just posted an in-depth review of the new Sigma 24-105 f4 OS lens, which is set to directly challenge the camera makers and their higher-priced optics. For serious shooters looking for an all-around solid performer, on paper, is the perfect optic.
So, how does it do in practice? Short answer: rather well.
Optically, the lens is pretty good. In terms of sharpness, the lens excellent right out of the f4 gate in the center but the corners lag noticeably. Remedy to the problem? Stopping down improves the corners a bit. Note: on APS-C format cameras, the corner softness is a much-reduced issue thanks to the smaller chip. Vignetting? It's very prevalent wide open, especially at 24mm. Stopping down does reduce the problem, but the overall trend is for vignetting to remain more prominent at shorter rather than longer focal lengths. Distortion? It's there, but is really no worse than comparable products from other manufacturers. Chromatic aberrations? Overall, they're more prevalent (though by no means obnoxious) at the shorter focal lengths and diminish with stopping down the lens.
Mechanically, the lens uses Sigma's HSM sonic-drive AF technology, which results in silent, virtually instantaneous AF. As for construction quality, the lens uses Sigma's new Thermally Stable Composite as well as metal which, according to Photozone, results in surprisingly good build quality on-par with manufacturer offerings.. Unfortunately, there's no rubber gasket at the mount, so don't go taking this lens out in harsh environments.
If there is one nitpick on this lens, it is its lack of weather-sealing and dual cam design for the inner barrel, which Photozone says could both impact the long-term survivability of the lens.
Overall conclusion? The Sigma 24-105 f4 OS is a good lens, but it doesn't deliver a 'wow' factor, either. When compared to the Canon 24-105 f4L IS, Photozone notes that, in term of performance, it's basically a draw. For Nikon or Sony shooters, though, the Sigma lens could be very. Very interesting.