Having a problem with my SB-600 speedlight. When I shoot several photos in succession, the light output gets progressively less and less. Is there a solution to this without upgrading my equipment? Or is upgrading equipment even a solution to this problem? I am using the best AA batteries I can buy, but the problem still exists. The obvious solution, of course, is to NOT fire off flash photos in rapid succession. There are times, however, that I need to do this. Comments?