I shoot with both a 5DM3 and a 6D, I am looking for a night photography lens. For night use, I currently use a Canon 16-35 f 2.8L II, a Sigma 24mm art f 1.4, and just bought a Rokinon 14mm f 2.8. I want wider than the 24mm Sigma, I usually shoot the Sigma at f 2.8 t do away with coma. The 16-35 is just not producing clean enough images, soft at the edges and a low resolution look to the images it produces, the Rokinon might be decentered, just cant get it looking sharp or in focus though close. I am considering the 20mm Sigma art f 1.4 and the Tamron 15-30 f 2.8. I was shooting both the Rokinon 14mm and the Sigma 24mm side by side last weekend in Yosemite, ....the Rokinon had fogged up half way through 90 minutes of continuous shooting, and the Sigma never fogged. So that got me concerned about getting either the Tamron or 20mm Sigma. Has anyone noticed excessive fogging middle of the night shooting with any lens having the bulbous type front elements? Coma on the Sigma 24mm I feel to be acceptable when shot at f 2.8, so has anyone owning both the 20mm and 24mm Sigma lenses been able to tell if one has less coma than the other?