When the Sigma ART 35/1.4 first appeared on dealer shelves, I put one on a camera very briefly and drew a few conclusions.  In the store, focus was very quick, as quick as the Canon 35/1.4 I use regularly I thought.  It was also very large comparatively speaking and felt very well built and a but heavy, that being a relative term for a guy who spends a fair bit of time waving fast telephoto primes around.  I had no card in my pocket so didn't make any test shots and then time moved on.  Recently there has been a resurgence for full frame shooters with interest in a fast 35mm, sometimes for street work and for others as their walk around lens.  So I arranged with my local Sigma dealer to obtain one for a short review.