see also:

• Canon EF lenses
• Sigma 12-24mm f/4 DG HSM Art full frame lens
• Sigma 24mm f/1.4 DG HSM Art full frame lens
• Sigma 24-35mm f/2 DG HSM Art full frame lens
• Sigma 35mm f/1.4 DG HSM Art full frame lens
• Sigma 50mm f/1.4 DG HSM Art full frame lens
• Sigma 50-100mm f/1.8 DG HSM Art APS-C/DX lens
• Sigma 85mm f/1.4 DG HSM Art full frame lens

• 20mm super wide angle full frame lens in various mounts
• world's first ƒ/1.4 ultra wide angle lens for full frame dSLRs (Nikon has a 20mm ƒ/1.8G lens, Sigma had a cheaper 20mm f/1.8 EX and then there is the Leica 21mm f/1.4, a $6,700 lens for rangefinders)
• no filter thread!
• not weathersealed!

• 20mm super wide angle full frame lens
• no filter thread!
• not weathersealed but will take a light shower
• Sigma uses a new material called TSC (Thermally Stable Composite)
• HSM AF
• close focus 0.276m giving 0.14x macro
• 15 elements in 11 groups, and includes 2 FLD (“F” Low Dispersion), 2 SLD (Special Low Dispersion) and 2 Aspherical elements
• 9 rounded blades
• 90.7mm x 129.8mm
• 950g
• $US900

• http://www.photozone.de/canon_eos_ff/973-sigma20f14art
  • 3.4EV vignetting, reducing to 1.85EV at f/2 and 1EV at f/2.8
  • 2.44% barrel distortion
  • very soft corners wide open, corners and centre sharpest at f/4
  • 1px CA - well controlled
  • far better bokeh than most wide angle lenses
• https://www.slrlounge.com/sigma-20mm-f1-4-art-review-a-wide-lens-in-a-league-of-its-own/
  • much less coma, blooming and astigmatism than the Sigma 24mm f/1.4 DG HSM Art full frame lens and sharper as well!
  • coma is an issue though until you stop down to f/2.8
  • there is some sort of weird field curvature or other blooming effect happening at f/1.4, through the whole image
  • awesome sunstars but the rounded blades mean points are not as sharp
• https://fstoppers.com/originals/sigmas-20mm-f14-art-pure-heaven-no-competition-unless-you-shoot-nikon-101810
• https://fstoppers.com/originals/sigma-20mm-f14-art-special-astronomy-review-104169
  • mild coma and astigmatism - acceptable for stars / Milky Way astroscapes
  • sharper than the Nikon and Canon 24mm f/1.4 lenses in the center, and at least equal in corner resolution
• http://zarphag.com/2016/01/the-sigma-20mm-f1-4-art/
  • for astrophotographic landscapes of the Milky Way, the Rokinon/Samyang/Bower 24mm f/1.4 manual focus lens has slightly better star shapes if you get a good copy, similar vignetting but less build quality, more copy variation, and less sharp in the centre, and of course, is not as wide angle and doesn't have AF or aperture control by camera.
• http://www.imaging-resource.com/lenses/sigma/20mm-f1.4-dg-hsm-a/review/
  • 1.5 EV vignetting wide open, 0.75EV at f/2.0 and 0.25EV at f/4
• https://www.ephotozine.com/article/sigma-20mm-f-1-4-dg-hsm-art-review-28425
  • very sharp wide open, best at f/2.8-f/4
  • well corrected CA 0.8px at edges
  • 2.14% barrel distortion
  • flare well controlled
• https://www.dxomark.com/Reviews/Sigma-20mm-F1.4-DG-HSM-A-Canon-mount-review-Tempting-new-addition