How fast is the focus speed of the Olympus 45mm in low light? Particularly compared to the 12-40, 17mm, and Nocticron. I just received the Nocticron and find the focusing too slow on my E-M1. I own the other 2 as well and they are very fast to AF, particularly the 17mm. I'm using it mostly to shoot my kids indoors. While the 12-40 is more than fast enough to AF, the 2.8 forces my iso higher than I would like. I wonder if the O45 will be better for me. 1.8 would be fast enough to get my iso down to an acceptable range.