Super tele lenses (400mm+) tend to be rather expensive being and as such often limited to professional use. However, there're a few lenses where the manufacturers were able to keep a rather moderate price level and the Sigma AF 120-400mm F4.5-5.6 DG HSM APO OS is surely among to more popular options...

I have owned this lens since July 2008. I use it for Pow-Wows, nature shots, wildlife. Its a great lens, very well built....I've dropped it from about 3 feet up and it hit the sidewalk, I thought I would be picking up pieces, but afterwards it works just like new.

Durable; Easily Interchangeable; Quick Focus; Rugged; Sharp Focus; Strong Construction

Heavy

A 3.3x zoom lens covering super-telephoto focal lengths, with optical stabilisation to aid hand held shooting.

Priced well; Good build quality; Optical Stabilisation; Silent focusing with full-time manual override

Prone to flare when used without the supplied lens hood; Loose zoom mechanism suffers with zoom creep; Hunts for focus in low light conditions

I have been using this lens regularly and have been very pleased with my photos. I am not a professional but I have been interested in photography since the 80's. This has been my biggest investment in a lens to date and I am very happy I went with the Sigma!

Not a bad lens for the money this Sigma can be quite sharp and reasonably quick to focus if you know how to use it and your camera to their maximum potential. This is not a point and shoot type of lens , it does require your input to get the best out of it.I found it quite heavy when lugging it all...

Cost effective; High build quality; Smooth focusing; Quiet,accurate HSM AF motor; Great adjustable tripod leg mounting shoe; Zoom creep lock

Soft wide open at maximum zoom/aperture; Heavy; Autofocus can hunt a bi,t but once locked on to the general target area is very fast

Yet another awesome lens by Sigma! I have yet to try it out outdoors but my tests from indoors are very promising! As always, Walmart has the best prices and service!!

Yes, I would recommend this to a friend

Clear Optics; Easy To Use; Firm Mount; Strong Construction

Slightly slow focusing

After reading many, many reviews of the Sigma 120-400mm lens and the Canon alternative, 100-400mm and taking into consideration the cost, I decided on the Sigma lens. If I was wealthier, or a professional, my decision may have gone the other way.

Durable; Easily Interchangeable; Strong Construction

Heavy

I have owned this lens for about a year now. I am very pleased with the images I get from it. I have found it hunts whilst focusing in grass or trees. I tend to use manual focus 10% of the time because of this slight problem. I would not say it is a fault.

I bought this lens for outdoor sports photography with my Nikon D7000 (The seller changed over the attachment to a Nikon one). Brilliant lens. The price is phenomenal compared to canon or nikon branded lenses of the same calibre.