Is the canon ef 100mm f 2 usm good in low light?

Yes, for low light the f/2 maximum aperture is the main reason to buy it. It gathers far more light than a typical kit zoom, so you can keep shutter speeds up or ISO down. It isn't stabilised, so the wide aperture and a fast shutter will do most of the work.

A bigger sensor helps even more. At the same framing and f-number, full frame gains roughly a stop over APS-C, so the Canon EOS 5D Mark IV or Canon EOS 6D Mark II will be cleaner at high ISO. On APS-C, the Canon EOS 90D or Canon EOS 80D still work well with it. Just remember that 100mm frames like about 160mm there, so it becomes a tight portrait or telephoto lens.

For the trade-offs, see Sensor sizes.

Written by Claude from this site's pages.