I recently purchased a used 28-70 f/2.8. I was shooting deer last weekend, and granted it was getting dark out, all the pictures came out blurry. I can't post the pictures right now. My question is this, the deer was at about 40 yards, Is there a maximum range my 2.8 aperture can reach out to? Should I have been using an aperture closer to 8 or 9 since the deer were further away?