Lens options for MR-14EX
I'ts not clear to me exactly what you've tried so far. Is the exposure too low when stopping down even when using the ringflash on full power? Is dof adequate when stopped down to f22?
If the answer to both questions is yes then crank up the ISO. More powerful (but less convenient) flash setups may be an option too. In general a different lens isn't likely to be helpful as most other macros have longer FL so dof is going to be narrower. As posted above for maximal dof a p+s is a good option because of their tiny sensors even if IQ is a bit lower. Shallow dof is an inescapable fact of life with extreme close up photos. What exactly are you shooting?