You asked
Is the canon ef 600mm f 4l is iii usm worth it?
It depends on what you shoot. A 600mm f/4 is wonderful for birds and distant wildlife, but the wildlife and sport guide calls big fast primes like this very heavy and very expensive. It only makes sense if reach is the thing you can't do without.
On a full-frame body such as the Canon EOS 5D Mark IV, it gives you 600mm as marked. If you want to carry less, the Canon EOS 7D Mark II is APS-C, where the lens frames like about 960mm on full frame. The Canon EOS 90D is another APS-C option. For most hobby use, my picks point to a 100-400mm-class zoom, and buying used is worth a look.
Written by Claude from this site's pages.