Leica M9 with 50/1.1 Nokton. ISO 2500, wide-open. 1.25x magnifier used. LR6 used with default NR, "25% color, 50% detail, 50% smoothness". Sharpening turned off. I find sharpening at High ISO brings out more noise. Slow 4x SD cards used, as always.
I suspect that Zeiss offered both collapsible and rigid at the same time, and this was the easiest way to offer a rigid lens: a one piece tube that adapted the collapsible barrel to the rigid mount. The mount still uses shims for the standoff, so the tube just has to screw into place- but not be an exact length.