Bought the Viltrox AF 50/2 for weight and size, and because it is free of distortion, flare, coma, CA, LoCA. It is very sharp in the center from f2 and from there it gets better and better as you stop down. The background is very pleasing, colour rendition is neutral. AF is not particularly fast, even in daylight, and it struggles to cath eyes in portraits. For the price the optical performance is incredible, just wished for an AF/MF button on the lens, and better overall autofocus performance (updated to the latest firmware).