Is the zeiss loxia 50mm f 2 good in low light?

Yes, for low light it's a good choice. Its f/2 maximum aperture lets in a lot of light for a 50mm, and that matters more in dim rooms than almost anything else. On a full frame body it frames as a normal 50mm. On APS-C it acts like a 75mm, with depth of field similar to f/3.

Keep two things in mind. It has no stabilisation and no autofocus, so you'll be focusing by hand and holding it steady yourself. Shutter speed matters more in the dark than the lens's aperture alone.

If you want a little more width, the Zeiss Loxia 35mm f/2 is also f/2. The Zeiss Loxia 85mm f/2.4 is slower, so I'd skip it for dim scenes. For the reasoning, see primes or zooms and is full frame worth it?.

Written by Claude from this site's pages.