R6-R7 Mirror lock up release?
The R6 re-introduced the ability to pre-release the mirror prior to tripping the shutter - prior to that, only the Leicaflex standard supported it. The idea behind this release is to lock up the mirror in order to prevent mirror-flap vibrations from spoiling telephoto or macro shots.
In order to operate the pre-release on a R6, R6.2 or R7, you have to use a 2nd cable release threaded into the small socket at the base of the lens mount block. Give it a squeeze and the mirror will flip up. Now press the shutter on top of the camera body to take the shot. Yes, you have to do this for every shot as there is no do-it-once-and-it-stays-that-way mirror lock-up. Very annoying and makes you wonder why Leica couldn't have a simple MLU lever like every Nikon F variant ever made.
To get around having to use a separate 2nd cable, Leica make a small release button which threads into this socket - it is called a Mirror lock-up release, part number 14 087, price $US 29. To use it, you screw it into the pre-release socket and press it lightly with your finger prior to firing the main shutter button.
However, $US 29 is pretty steep for a little screw-in button. Instead I use a large straightened-out heavy duty paper clip, which is much cheaper and there is less chance of bumping the camera when doing the pre-release. Just poke the end of the clip into the hole and press lightly - works every time.
Thanks to "Michael Gardner" <firstname.lastname@example.org> for this tip!