If the aperture number increasing or decreasing?
To reduce exposure, you can reduce the size of the aperture (i.e. change from f5.6 to f32), you can increase the shutter speed, and you can reduce the ISO number.
You'll probably need to be in manual mode to control all three.
I am using the new Nikon D200. I am shoot white egrets and swans and my whites are getting "blown" partially due to the time of day I am shooting. I am looking at the histogram and it tells me I am losing detail in the whites and the highlight indicator blinks on the playback of the image. So I get the feedback of the problem.
But, the problem is not corrected by stopping down one third; two thirds, a whole stop or lowering the iso to 100. What else would you do to stop your whites from getting blown? I know I can correct the problem by shooting early in the a.m. or late in the day in softer light, but if you are traveling you don't always have that option, so I am trying to figure out how to shoot for that contingency. Thanks.

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