I had some Schneider Kreuznach DKL lenses made for Kodak Retina then I paid the price hurdle (almost to high to jump over) and was rewarded by the most exquisitely made lens adapters I have ever seen. Yeenon had replicated the build of the female part of the DKL mount and the aperture mechnism faithfully and precisely right down to the materials used. This was a M42 mount adpation but they make others. When mounted the adapter is such a faithful replication that it is impossible to tell that the lens was not made as an OEM M42 lens. Even the little red “trick” moving dof indicators are there and adjust automatically to suit the maximum aperture of the lens.
I have called Yeenon adapters “jewel like” and I have no reason to resile from that.