I loved my panasonic 20mm pancake - image quality and size. However, i sold it because of its awful low light focusing speed. I shoot my kids playing indoors and it just didnt work out. Oly 17 mm f1.8 fits the bill. But it's so much larger... I know there is a technical reason that makes the 20mm slow, my question is, is that the same reason that makes it small? Is it possible to have oly 17mm speed in a pamy 20mm size? I know the 17mm f2.8 and the 14mm... I'm asking about fast lenses, say, below f2 Thanks!