As the final duel is fought, the duelists have light on the sides of their bodies away from the sun - Sasaki has light on his back and Miyamoto light on his face.
In one shot as he is rowed away, the background behind Miyamoto does not move as the boat moves.
Musashi arrives at Ganryu Island by boat, and we see it as he wades to shore. After the duel, we see it out in the surf as he wades back. During the duel, however, it is completely absent.
When Okaya is fighting Sasaki, the position of his spear when he removes the covering changes between the close and the long shots.