Sigma is clearly playing with the idea to launch a a wide angle Full Frame lens with constant f/1.8 aperture. The patent shows the specs and design of three slightly different versions:

• 15-24mm f/1.8
• 16-28mm f/1.8
• 18-30mm f/1.8

If you wonder how BIG this lens would become, the specs say the length is about 16cm. That’s 4cm longer than the Sony 16-35mm f/2.8 GM lens.
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via Digicameinfo