The 50A follows Sigma’s new design philosophy first introduced in the 35mm 1.4 Art ( a benchmark lens that put Sigma back on the map for many photographers). Though the exterior of the lens is plastic, it feels very well put together with tight tolerances and high quality workmanship. The intimidating weight also adds to the feel of quality - the lens feels more like a 24-70 f 2.8 zoom rather than a modest 50mm prime.
Featuring a mostly-metal construction, the lens feels solid and much better than any of the 50mm lenses of Nikon and Canon. The only notable omission from the otherwise stellar build is the complete lack of weather sealing. This is something to keep in mind if you intend to use the 50A in less than perfect weather.Handling
This is the one category where I believe this lens suffers. The sheer size and weight of the lens ensure that a photographer needs to be prepared for fatigue after a long day’s shooting. Also, if paired with a lighter camera body, the combination is uncomfortably front heavy and causes a signifiant strain on the wrist. Paired with a more substantial body, such as the Nikon D810 or the Canon 5D3, the lens is far more tolerable.Autofocus The autofocus of the Sigma 50mm Art is much improved over the older version of this lens - the 50mm EX DG HSM. However, like most of the Sigma lenses I have owned, the 50A required a fair amount of focus micro adjustment calibration. If you intend to purchase or rent this lens, it would be best to pair it with a body that supports micro adjustment or the optional Sigma lens calibration dock. After calibration, AF accuracy was good to excellent in most cases. Weddings, my primary use case for this lens, provided an excellent opportunity to put the AF through its paces and I was generally quite satisfied with its performance. There were times, especially in low-light, where the lens struggled but those occasions were few and far between. Image Quality Without resorting to using MTF charts, the easiest way to describe the image quality of this lens is “superb”. The bokeh is smooth and very appealing and the lens renders wonderfully sharp images right from f1.4, requiring very little additional sharpening in post processing. Stopping this lens down to f/2 and 2.8 give you images that are incredibly sharp. Conclusion Overall the Sigma 50A represents the best combination of optical performance, build quality and price. The only lens close to this quality for a dslr would be the mighty Zeiss 55 1.4 Otus - a lens that costs more than 4 times more, is larger and is manual focus only.
If you ever wondered what the bleeding edge of optical quality looks like, I highly encourage you to check out this lens.