Hi ....(this will be little lengthy)...I have posted here before regarding the Sigma 50mm and the 35mm Art Lenses.
I own both and with some hesitation and quite a bit of attention to getting the lenses to perform consistently well.
I bought the 35mm Art first and I did not really test it at first...I was amazed by the sharpness. I am more an artistic photographer than I am a measurebator. ... I also bought the 50mm Art (when I could finally get my hands on one), and I was well aware of the focusing issues when I purchased that lens. I also bought a the Sigma Lens Dock when I bought the 50mm.
Here is how I test...I shoot specific images just for the testing and I will shoot a specific spot close and a specific spot much farther away. I repeat this a few times and look at my results. I use center focus points and edge points. I use a "Show Focus Points" Plug-in in LR so that I know exactly where I focused. (I will mention that both my "Show Focus Points" Plug-in and Canon's DPP show the focus point location on my computer screen slightly to the right of where I actually focused using the camera (5DIII). This is consist with every shot. There is a half to about 3/4 of a focus point shift from my camera to the two softwares I use on the computer?
(Does anyone else experience this?)
Anyway...My 1st 50mm Art was all over the place and I could not get it to focus consistently. After wasting hours of my life ...I returned the lens to B&H, explained the situation (which they were well aware of) and they gladly sent me another lens. The 2nd lens was MUCH more consistent....and needed just a slight bit of tweaking on the Sigma Lens Dock (I did not touch the focus adjustment in the camera). I have used the lens quite a bit and it is consistently accurate wide open...Any issues I have are to do with operator error...I think that this lens is just fantastic. (but I worry about it shifting because of all I have read.)
OK...the 35mm ...Needed a LOT of adjustment on the Dock +13 in all 4 zones. At least it was consistently of and I could have used the AFMA in the camera to straighten this out as well. I must say I am a little disturbed and how big this adjustment is. It leaves me uneasy. ...but the lens seems to perform consistently well now that I have taken the time to adjust it.
Now ...I do not sit around with charts and..blah..blah blah... I use the lenses to go out and shoot images. ...and when I am shooting wide open I check my focus point occassionally and the lenses seem very accurate....and i just love the IQ...Especially for what I paid.
Its a drag to have to do all of this work...but in my case I feel that it was worth it. Both these lenses are capable of creating really great and unique images!!!