> do I need an adapter Building on that, Canon RF 100-400mm f/5.6-8 IS USM clicks right on. Unfortunately, f/8 is dark. You could adapt an older Sigma 150-600mm f/5-6.3 Contemporary but it's way heavier.

I'm so satisfied with the Canon RF 600mm f/11 IS STM for birding. I carried it all day at the lake and barely felt it, plus no adapter is needed.

> I looked online and all the numbers like 100-400 or 600mm just make my head spin and I'm so scared of spending my savings on the wrong thing. Honestly, I felt the exact same way when I first started out with my R7. Last summer I took a trip out to the Tetons and brought along the Canon RF 100-400mm f/5.6-8 IS USM. It was a total game changer for me. I managed to get some incredible shots of a moose from across a river and my arms didnt even get tired since the thing is basically weightless compared to the old professional glass. It clicks right onto your camera without any adapter because its an RF mount lens. Quick tip for Yellowstone: make sure you enable animal eye tracking in the autofocus menu. It makes catching birds in flight way easier. Im super satisfied with how sharp my photos turned out, zero complaints here. For about $650, you honestly cant beat the value for wildlife.