You asked
What cameras fit the leica vario elmar sl 100 400mm f 5 6 3?
The Leica Vario-Elmar-SL 100-400mm f/5-6.3 fits a long list of bodies, all on the L-Mount. Full-frame choices include the Leica SL3, Leica SL2-S and Panasonic Lumix S5 II. If you shoot wildlife or sport and want a lighter setup, the Panasonic Lumix S9 is a sensible pick. On APS-C, the Leica TL2 and Leica CL take it too, and it then frames like 150-600mm on full frame.
My own pick for reach is a full-frame body like the SL3-S or S5 II. The lens is stabilised and autofocuses, so it works well for moving subjects. Long lenses also hold their value on the used market, so buying used can save you a lot. For a sense of what focal length you need, see Wildlife and sport.
Written by Claude from this site's pages.