Like a lot of photographers who use 50mm F/1.4 primes, I often wonder if it could be a little sharper wide open or focus a little more accurately. While I was getting to know my new 24-105 L zoom last month, I decided to send my Sigma 50/1.4 in to Sigma for a little TLC under warranty. I've had it for about two years.
On the repair request, I said that it was not as sharp as I wanted wide open and it did not focus as accurately as my Canon lenses. I figured that would challenge them a little.
I got the lens back exactly two weeks after I sent it, which means they had it in the shop about 3 working days, by my estimate. Pretty impressive.
The service invoice says they "adjusted af data"
If there is any improvement in performance, my methods are not adequate to detect it, but I do feel better knowing that the lens is properly calibrated. It's a confidence thing, you know.
This is still one of my favorite lenses, along with the Canon 85mm F/1.8.