Sigma's budget super-telephoto zoom — 120-400mm reach with HSM autofocus for wildlife on a budget.
The Sigma 120-400mm f/4.5-5.6 APO DG OS HSM was released in 2007 as an affordable super-telephoto zoom for full-frame DSLRs. Covering 120-400mm with optical stabilisation, it offered serious telephoto reach at a fraction of the cost of the professional 100-400mm lenses from Canon and Nikon, appealing to budget wildlife and sports shooters.
Optical performance is good for the price class. Centre sharpness is respectable throughout the range, particularly at 120-300mm. The APO designation indicates apochromatic elements for reduced chromatic aberration. OS stabilisation provides approximately 4 stops of correction. HSM motor is fast and quiet with full-time manual override for fine-tuning focus.
Available in Canon EF, Nikon F, and Sony A mounts. Filter thread is 77mm. Weight is approximately 1,640 grams — heavy, requiring a monopod or tripod for extended use. A tripod collar is included. Build quality is solid with a zoom lock switch. No weather sealing. The lens extends significantly at 400mm.
Available on the used market at very attractive prices — often well under £300. Check for smooth zoom operation, OS motor function, and AF accuracy. The weight is the main drawback for handheld use. An excellent budget gateway to super-telephoto photography. The Sigma 150-600mm Contemporary has largely replaced it in the lineup.