The Tokina 12-24mm f4 is a lens designed for APS-C sensor D-slr's. It's full frame equivalent is approximately 20-40mm. If you are switching from APS-C to full frame you may think that you are faced with the task of replacing it. A Tamron 20-40mm or Tokina 20-35mm are obvious choices. But, do you need to replace it? The answer is No. The Tokina 12-24mm f4 is usable on full frame D-Slr's. In fact, there is no vignetting from 18-24mm and there is less distortion in that range compared to 12-16mm on an APS-C sensor body. Ofcourse it is just an 18-24mm but that is all you need. You probably have a 24-70mm or 28-135mm already. You may be skeptical. See examples below. Notice that the full frame images have a shorter depth of field which gives a blurrier bokeh. Why would I sell a lens that gives me excellent images on two systems. I prefer the shallower depth of field when using it on the 6D. Also, it is difficult to find an ultrawide zoom that focuses down to 6 inches. I thought I wanted a Tamron 20-40mm. I changed my mind. I am keeping my Tokina.
Canon Eos 6d full frame body @ 19MM w/ hood. Approx. 6 inches away.
Canon Eos M3 mirrorless APS-C body @ 13mm w/ hood. 6 inches away.
Eos 6D @ 18mm w/ hood.
Eos M3 @ 12mm w/ hood.
Eos 6D @18mm w/ hood. Distortion is present bu well controlled for 18mm.
Eos 6D @ 18mm
Eos M3 @ 12mm