I just need this cleared up. So many people say it different I'm not sure who's right. With micro 4/3rds they say double focal length so my f1.7 20mm is (40mm equivalent to 35mm) but some people will say its f3.4 40mm. Should you double aperture value? does that mean my great 20mm lens at f1.7 is only really letting the same light and bokeh as a 40mm lens at f3.4 (I mention bokeh as someone was surprised I shot at f1.7 and the background looked more like f3-4 to them)?