Not a perfect example, sir
I encourage you to look at the following page instead:
http://www.the-digital-picture.com/Reviews/Sigma-50-100mm-f-1.8-DC-HSM-Art-Lens.aspx
"... Once calibrated, the Sigma 50-100 f/1.8 turned in excellent focusing consistency when focusing at both ends of the focal length range using the center AF point... "
I had only a limited first hand experience with the 50-100 and just recently but can confirm that center AF point consistency was very good with the lens. The AF feels much snappier than with older Art lenses.
In my humble opinion, Sigma decided to test new AF system on the APS-C zoom heavy lens and only then use in 85mm, 24-70 and 70-200 FF lenses as they cannot afford dropping the ball with this trio. it has to be perfect this time.
P.S. The Sigma 85mm Art lens page is up at Sigmaphoto US:
https://www.sigmaphoto.com/85mm-f14-dg-hsm-a
MTF Charts, Distortion Guide and Vignetting (very impressive if true):
http://www.sigma-global.com/en/lenses/cas/product/art/a_85_14/data/
the good old 50 F1.4 Art MTF chart for comparison:
New HSM AF motor and dust splash proof construction details:
http://www.sigma-global.com/en/lenses/cas/product/art/a_85_14/features/#features03
Alangeli said:
According to Tony Northrup the Sigma 50-100mm f1.8 seems to be very inconsitent in its AF accuracy:
https://www.youtube.com/watch?v=YgIMVjOXfKo
Alex_M said:
yes, that was the issue with the 24, 35, 50 Art lenses. 50-100 F1.8 was the first, IMHO, Sigma Art lens to receive the new updated AF motor and AF consistency improvements are noticeable. so once again, there is a hope that 85Art is a better focusing lens. with regards to 85 Art being expensive, I suspect that it will be in the Otus 85mm image quality territory. I am very tempted but will wait until The Digital Picture review availability.
P.S. I thought that the larger front element usually helps to reduce vignetting and sharpens the corners. Not so sure about CA.