Dxo has posted review of Sigma 500 f4 basically nearly on par with Canon's own 500mm f4 II IS.
https://www.dxomark.com/Reviews/Sigma-500mm-f-4-DG-OS-USM-S-Canon-lens-review-Super-sharp-shooter
Conclusion (from DxoMark)
Big, heavy, and expensive, a 500mm f/4 super telephoto is truly the preserve of the professional or extremely serious wildlife and sports photographer who requires plenty of reach, a fast aperture, and super-sharp results. As such, there are only a few such lenses available, but Sigma’s third-party 500mm f/4 gives photographers an alternative to Canon’s own-brand option.
The Sigma 500mm f/4 comes equipped with the advanced features the pros demand to enhance performance, including a focus limiter, focus recall buttons, image stabilizer, large lens hood and tripod collar for mounting to a monopod and quickly switching between vertical and horizontal shooting positions.
In terms of image quality, the Sigma 500mm f/4 is excellent, delivering high levels of uniform resolution on all the professional full-frame EOS 5DS R, 1D X Mark II, and 5D Mark IV DSLRs, with no geometric distortion nor problematic chromatic aberration to worry about. There’s some vignetting at the maximum f/4 aperture, but at around –1EV, this isn’t overly concerning and corner shading is virtually eliminated from f/5.6.
Head-to-head against the Canon EF 500 f/4L IS II USM, the Sigma 500mm f/4’s image quality compares very favorably. The Canon lens is fractionally sharper on the 5DS R, but the Sigma offers a modest improvement in resolution on the 1D X Mark II and 5D Mark IV. To be fair, there’s very little to separate them in real-world terms on any of these DSLRs, however, making the Sigma 500mm f/4 a great value option.
https://www.dxomark.com/Reviews/Sigma-500mm-f-4-DG-OS-USM-S-Canon-lens-review-Super-sharp-shooter
Conclusion (from DxoMark)
Big, heavy, and expensive, a 500mm f/4 super telephoto is truly the preserve of the professional or extremely serious wildlife and sports photographer who requires plenty of reach, a fast aperture, and super-sharp results. As such, there are only a few such lenses available, but Sigma’s third-party 500mm f/4 gives photographers an alternative to Canon’s own-brand option.
The Sigma 500mm f/4 comes equipped with the advanced features the pros demand to enhance performance, including a focus limiter, focus recall buttons, image stabilizer, large lens hood and tripod collar for mounting to a monopod and quickly switching between vertical and horizontal shooting positions.
In terms of image quality, the Sigma 500mm f/4 is excellent, delivering high levels of uniform resolution on all the professional full-frame EOS 5DS R, 1D X Mark II, and 5D Mark IV DSLRs, with no geometric distortion nor problematic chromatic aberration to worry about. There’s some vignetting at the maximum f/4 aperture, but at around –1EV, this isn’t overly concerning and corner shading is virtually eliminated from f/5.6.
Head-to-head against the Canon EF 500 f/4L IS II USM, the Sigma 500mm f/4’s image quality compares very favorably. The Canon lens is fractionally sharper on the 5DS R, but the Sigma offers a modest improvement in resolution on the 1D X Mark II and 5D Mark IV. To be fair, there’s very little to separate them in real-world terms on any of these DSLRs, however, making the Sigma 500mm f/4 a great value option.
