Exercise 7 - Object in different positions in the frame

The task today was to take 4-5 shots of the same object putting it into different areas of the frame. Here is my stone that I have chosen for this exercise.

The first picture is with an object in the centre. The shot has been take at f/8 aperture and shutter speed 1/200s. Focal length - 26 mm.

Here is the second version. The stone is a bit to the left. Settings were the same as for previous shot.

The third shot with a stone closer to the right bottom angle. For this shot I changed settings a bit: f/8, shutter speed 1/3200, foal length changed to 26mm.

And the forth option with the stone in upper left corner. Aperture f/8, shutter speed 1/1600s as the angle of light has changed and focal length 26mm.

Looking at all four shots, I would conclude that I like the composition of the third one the most. The stone itself is not very exciting object to put in the middle of the frame. The second shot makes me nervous on some subconscious level. It does not put emphasis on the object and attention is driven from the background as well.  The fourth shot shows a bad choice of the background (sand in this case is not very nice thing to look it), and the stone would look better if it was put a bit lower in the frame. Te third shot looks the best to me. It does not take attention completely from the stone, but shows beautiful sea on the background as well. It might be that if I had put stone a bit upper, it would look slightly better, as it would be exactly two thirds rule.