Jaime wrote:
In order to have complete control, you need to turn off auto ISO and shoot manual. The camera's brain wants to give you a consistent picture from shot to shot, so when you increase your shutter speed a stop, the camera compensates by moving your ISO a stop to keep the exposure equivalent. Turn off auto ISO and shoot manual and you will get the desired effect as the camera's brain will then say, "Okay, wise guy... you drive." Good luck.
Thanks Jamie. I actually was shooting manual -- or so I thouight. I selected shutter speed, f/stop, and ISO setting -- except I didn't realize there was an overriding force at work for ISO. Appreciate the feedback.