Here's some interesting math: at widest setting the X10 lens has a 3.55 mm max aperture, and at longest setting the max aperture is 10.1 mm.
Compare this to a typical m43 kit zoom lens like the Panasonic 14-42/3.5-5.6, with 4 mm aperture at widest and 7.5 mm aperture at longest focal length.
Two conclusions from this (ignoring the fact that wide and tele ends have a bit different angles of view):
- X10 lens is able to defocus to at least the same degree as a m43 kit lens;
- X10 lens captures at least as much light as a m43 kit lens, which despite difference in sensor size should be reflected in sensitivity and noise levels being comparable. In theory, that is - for a given shutter speed a lower ISO can be used on X10.
I think that's what people are seeing in actual use?