I have always been steered well by the FredMiranda site's product reviews, and did my homework on this, searching for the "Mark I" version of this prime.
I suppose it is not right to complain about the quality when one has paid such a bargain price, but...
I bought this to have something lightweight and less intimidating for my subjects. It *is* light, and it *is* nice to have the 1.8 aperture.
Firstly, I am used to better speed and accuracy in my lenses ' autofocus ( I have been spoiled by my 17-40 L and Tamron 28-75). It searches quite a bit in low light, and taking pictures in low light is what I bought this for.
Second, I just don't get sharp images with this at any aperture setting. I may be missing something here, but this has been a disappointment.