agillot wrote:
For smaller birds , 800mm is it [ that is what is use , 800 f8 older 80 s] .On the other hand large birds , the zoom is more flexible . You can be too close with a fixed 800 on a blue heron , the zoom would fix that .So the ideal would be a 150 / 600 .
I had the 150-600mm Tamron when I purchase the R5 and adapter. I could not get the lens to focus correctly with the R5. I gave up, sold it and got the RF 100-500 instead. Not a single regret.