One reason I went for the 21 lux is for covering music clubs with all their dark, dark, splendor. Here's a series from last weekend on the M9, Iso generally 2000, wide open with shutter speeds of 1/15 and occasionally slower. One incidental finding was that the Zeiss 21 finder, which I have praised, actually helped quite a bit because it was so bright it made framing much easier! best....Peter