You asked
Leica summarit m 50mm f 2 4 vs leica apo summicron m 50mm f 2 asph?
The two are close cousins. Both are 50mm lenses for full-frame Leica M bodies, both are manual focus, and neither is stabilised. The difference is aperture and build. The APO-Summicron-M 50mm f/2 ASPH is faster, small, and extremely sharp, so it's my pick if you can afford it. The Summarit-M 50mm f/2.4 comes from Leica's lower-priced Summarit line, which is discontinued, so you'll be looking at the used market.
Choose the Summicron for dim rooms, shallower depth of field, and the sharpest results. Choose the Summarit if you want a 50mm on a Leica M for less and can live with the slower f/2.4.
Either lens fits bodies such as the Leica M11 and the Leica M (Typ 240). For what a 50mm does well, see portraits.
Written by Claude from this site's pages.