The Loxia and the Milvus are both MF 2.8/21mm for Sony?
How to they differ?
Is there an AF option too?
Completely different lenses, the Milvus lineup is for Nikon and Canon DLSR cameras and the Loxia lineup is dedicated for the Sony E mount with most lenses based on their Leica M variants so the designs are mirrorless from the start. The Loxia is a lot smaller and weighs roughly half the weight of the Milvus counterpart.
This the first 21mm for the a7 series and manual focus only, its fully modernised however so EXIF, focus distance, aperture, etc are communicated to the camera.