re: Zooming but not too far
It was in manual (in order to focus with the ring) and that also means no more automatic stabilizer.
I was in the attic (not very stable floor and partly inside with the open window).
I also use a tripod and delay the shots by several seconds, so I don't touch the camera.
You're right that perhaps the 300mm shouldn't zoom all the way. That way, there would be more room when I move the ring to find the sharpest picture.