You asked
What are the alternatives to the leica apo summicron sl 75mm f 2 asph?
The two closest alternatives in the same Leica line are the Leica APO-Summicron-SL 50mm f/2 ASPH, a wider and more everyday choice, and the Leica APO-Summicron-SL 90mm f/2 ASPH, a tighter view that suits portraits and subjects you want to keep at a distance. Both are full frame f/2 primes, so they match the 75mm's brightness and fit neatly alongside it.
If you shoot APS-C, the focal length converter explains why the same lens frames differently on each sensor. A 50mm on APS-C, for example, looks roughly like a 75mm on full frame.
For a sense of how focal length changes people pictures, the Portraits guide walks through the options.
Written by Claude from this site's pages.