Sigma 10-20 F4-5.6 HSM EX.
Sigma's ultra-wide offering for APS-C cameras is a bit of a controversial offering. Anecdotal experience suggest that when it was first released a large number of early examples had issues which necessitated sending the lens back to Sigma for fixing. If you got a bad copy you were stuck with unacceptably soft images unless the lens got sent back for re-alignment. Other reports deride its build quality - and question why anyone would want to attach a Sigma lens to a Canon camera. Sigma have come on in leaps and bounds in lens technology and performance and lens geek tests show that its performance is at least as good or better than Canon's 10-22 EF-S. Given that the Sigma was over a hundred pounds cheaper (and the current exchange rates mean that currently this difference is even bigger) I decided to plump for the Sigma.
Whilst Sigma's EX designation is their equivalent of Canon's "L" the build quality simply isn't up there with, for example, Canon's full frame 17-40 equivalent. It is still very good however and streets ahead of consumer grade kit offerings. It also comes with a lens hood - and although I've never used it - a belt pouch for the lens. Sigma are also currently offering an extended 3 year warranty (online regsitration required). Despite the excellent build quality the lens still feels fairly light and compact. Its silent to focus and the zoom ring is nicely dampened. As you'd expect the front element doesn't rotate - so using a polariser is no problem. Filter size is the ubiquitous "L" 77mm.
Distortion is well controlled throughout the entire range of the lens and its sharp when stopped down. Its a little soft wide open at 10mm but if you're using it for landscape work you'll be stopping it down to get the maximum depth of field. By F8 the image quality is stunning. Whilst I've not used this lens as extensively as my others (it was initially bought for a trip to Scotland that was plagued by bad weather) when it has been brought out it has produced pin sharp images. For long exposures I find that I need to use mirror lockup as my copy will occasionally show a little softness otherwise - although this does seem to be the case with long exposures and wide angles in general.
Be aware that when I used it with my Hi-Tech ND grads and a standard filter holder I saw vignetting at 10mm. Using a Cokin P Wide Angle Holder I get none. In my opinion this is a well made high quality piece of glass. If you want a wide angle lens on an APS-C camera the only other alternative is the much more expensive Canon. The Sigma gives you the equivalent of 16-32mm and the extra money for a 16-35mm equivalent just doesn't add up. I'd recommend getting this from a local dealer or at least one with a returns policy as there are reports of bad copies.
So given the great performance why isn't it in my current kitbag ? Once I'd picked up my 24-105 the difference in colour and sharpness was apparent. The Sigma certainly isn't soft - but it lacks the punch of images produced by the 24-105 and the colour and contrast lacks the "pop" of the L series lens. You can push it back in RAW but I much prefer the natural colour "out of the box" of the L lenses. Images sat next to those taken with a 17-40 definitely didn't have any where near the stunning colour that it (and the 24-105) produce. Its hard to explain but the colours from my "L's" look vibrant and natural. You have to push the colder feeling Sigma images saturation and vibrance in RAW and the effect just isn't as nice when it comes to landscape work - where often accurate colour rendition is vital. I've clearly been spoilt.
I've found my 24-105 wide enough for my current needs and as this was left at home ever since the Scotland trip - coupled with my issues with how it captures colour - it was simply surplus to requirements.
Pros : Well built, lightweight, well built, excellent value for money - sharp !
Cons : Possibly poor copies out there. Excellent image quality until you put it up against Canon's best.
Conclusion : Excellent value if you need this range and aren't bothered by the cooler less saturated colour.