Tokina's fast full-frame ultra-wide zoom — constant f/2.8 from 16-28mm with solid optics for the price.
The Tokina AT-X 16-28mm f/2.8 Pro FX AF launched around 2010 as a budget constant f/2.8 ultra-wide zoom for full-frame DSLRs. It offered professional-grade f/2.8 speed at a significantly lower price than the Canon 16-35mm f/2.8L and Nikon 14-24mm f/2.8G.
Optically good for the price — sharp in the centre with well-controlled distortion. The constant f/2.8 is useful for astrophotography and low-light work. Edge performance is adequate but trails the Nikon 14-24mm. Internal focus motor for Canon EF mount provides quiet autofocus.
Canon EF mount. Bulbous front element — no standard filter thread. Weighs approximately 950g — heavy. No weather sealing. Full-frame coverage. Minimum focus distance 28cm. The 16mm wide end is wider than the Canon 17-40mm f/4L but not as wide as Nikon's 14-24mm.
Available used at budget to mid-range prices. The bulbous front is the main practical limitation. The Tamron 15-30mm f/2.8 VC is a newer alternative with stabilisation and filter-compatible design. Good for astrophotography on full-frame Canon DSLRs on a budget.