Sigma's extreme super-telephoto — the 800mm f/5.6 for Canon EF professional wildlife.
The Sigma 800mm f/5.6 EX DG APO HSM is Sigma's largest super-telephoto prime for Canon EF-mount full-frame DSLRs, providing extreme reach for professional wildlife and aviation photography. APO apochromatic glass controls chromatic aberration at this extreme focal length, DG confirms full-frame coverage, and HSM provides fast autofocus.
The lens delivers 800mm at f/5.6 maximum aperture with APO glass construction for colour accuracy, HSM autofocus for fast subject tracking, EX professional build with robust weather sealing, and Canon EF coupling. Physical size is substantial, requiring tripod or monopod support.
The 800mm focal length is at the extreme end of practical photographic telephoto lenses, used for professional wildlife photography requiring great distances from subjects (elephant herds, ocean wildlife), aviation photography, and sports where the photographer must be positioned far from the action. The f/5.6 aperture is fast for a lens of this length.
Test HSM autofocus tracking at maximum aperture. Inspect APO element condition. Check tripod collar rotation and locking. Examine the large front element for any impact marks or coating damage. An 800mm lens should be stored in its flight case when not in use.