I was asked a question yesterday about DOF and the effect it can have on an image so I went out to see if I could find a subject that demonstrates the extreme lack of depth of field with a telephoto lens. Just for a thought this lens is a Zoom but at 300mm and f/5.6 your hyperfocal distance, or the closest focusing distance that allows objects at infinity to be acceptably sharp, is about 530 meters.
So, in this case, I am using using a full frame camera and a 300mm lens at 270mm and f/5.6 with a subject at a distance of about 1.5m from the camera sensor. There is approximately 1cm DOF available and there is probably 1.5cm depth difference between the small white silver back spider (top left) and the large spider on the bottom right. So the large spider is out of focus with the small in focus. BTW difficult to focus but the 5DsR is exemplary, view at full size: