My primary interest is water bird photography, I often use gears like 600mm f4 with 1.4x tele on a FF body with a sturdy tripod. But occasionally I will use a less heavy lens on a APSC camera when I bike along my way. I have both 200-500mm, new 300mm f4 with a 1.4x on the D500 body, I found the the 300mm with 1.4x on D500 is better in terms of sharpness, focusing accuracy and pleasancy to carry around. For some reason, I also have the new tamron 150-600mm on 80D or canon 5d4/ 1Dx2, the tamron is soft towards the 600mm.
