It would be useful to know how close you were to your still life, but a DOF calculator can help you to see if the actual DOF of your 300mm lens is as much as you thought it would be. Here is one that is easy to use, in 'camera' scroll down the list until you reach 8x10 and put in the other info and your DOF will be displayed

http://www.dofmaster.com/dofjs.html

Steve