viggo how much sharpening are you adding to those images in LR?
The Sigma doesn't seem to like Ai Servo, so I more often tap the button that switch to One Shot and it does the trick. It's slowly turning into a winner here.
This sounds more in line with what I am experiencing with my 50 Art. I generally do not like Ai Servo, so I only use it when it is absolutely necessary, which it hasn´t been yet during the first 10 days of using the 50 Art :-).
I mostly use One Shot AF, with single point spot focus and AF priority (not release priority). With this setting I have consistently good focus behaviour with the Sigma Art 50. I typically shoot portraits, so most of my targets are at 0.5 to 1.5 meters distance, and holding quite still. Also, I typically shoot with sufficient available light to get good exposures at ISO 100 - ISO 400. It is a situation that is not challenging the AF system very much, but at f/1.4 the DoF is very narrow, especially when the subject is close to the camera, so even slight AF inaccuracies will ruin the shot.
Only when subjects are moving too much for me to aim the point of focus in an exact manner I switch to single point focus without "spot", but still i usually prefer to One Shot AF when the movement is slow. I only took a few pictures with that settings so far, and they seem OK, but it is not a good basis for concluding. In any cases, subject motion makes it difficult to objectively blame the lens of any focus misses.
My skill with Ai Servo is too basic to conclude on lens focus performance. It seems to depend solely on my ability hold the camera stable, while pointing at more or less the same location on the moving subject. I would not blame the lens for any focus misses in such situations. I always expect quite a few shots at moving targets to be OoF at f/1.4.
I am very happy with the 50 Art AF performance at the moment, after tuning it in the Sigma USB dock.
