Conclusion: While no lens of this power is going to be compact, the Sigma is as light and short as you could reasonably expect. Like any long, weighty telephoto, ideally you would always combine this lens with the stability of a support. This isn’t always practical, though, particularly when shooting wildlife. Thankfully, due to the effectiveness of the OS technology, this is a lens you can confidently use handheld at two or three stops slower than would otherwise be possible.
Summary: Being priced at £675, this lens represents a good value choice for those looking for a super-telephoto lens, without the extortionate price tag associated with some camera manufacturer's own lenses in this range. For it's price, it has excellent build quality and a good range of useful features, such as Optical Stabilisation and silent focusing, but some aspects of handling could still be improved, like the looseness of the zoom mechanism.
Pros: Priced well, Good build quality, Optical Stabilisation, Silent focusing with full-time manual override
Cons: Prone to flare when used without the supplied lens hood, Loose zoom mechanism suffers with zoom creep, Hunts for focus in low light conditions
Excerpt: Originally posted 2008-06-16 on Optyczne.pl Lenses whose focal lengths start at around 100 mm and end at 400 mm are interesting proposals for many advanced photographers. While instruments of 70-300 class, by virtue of their affordable price and still acceptable dimensions, are often chosen by beginning amateurs as a supplement of the kit lens, are an appliance whose focal length ends at 400 mm, are a totally different caliber.
Cons: too weak image quality at 400 mm,, large weight and dimensions compared to the competition,, bad work against bright light,, mediocre accuracy of the focusing mechanism.