You asked
Leica apo summicron m 50mm f 2 asph vs leica summicron m 50mm f 2?
Both are 50mm f/2 primes for full frame Leica M cameras. They're manual focus, not stabilised, and fit the same long list of bodies, from the M9 through the M11. The choice comes down to how much you want to spend.
The Leica APO-Summicron-M 50mm f/2 ASPH is the one to get if you want the sharpest version of this lens. It's small and extremely sharp.
The Leica Summicron-M 50mm f/2 is the classic small 50mm and costs less than the APO. For most people shooting street, portraits or everyday life on an M body, it's the sensible buy. The difference in price can go towards a spare battery or a few rolls of film.
If you're still deciding on a 50mm in general, the portraits guide explains why this focal length is such a good first choice for people.
Written by Claude from this site's pages.