I've posted previously that I use the Auto ISO setting on my Nikon D700 when shooting sports. While shooting indoor sports, however, I'm not sure Auto ISO is always best (As a reminder, I normally use the Auto ISO setting when I manually set the shutter speed I want to achieve and an appropriate aperture setting (see post here). On the Nikon D700, an ISO setting as high as 6400 still produces very acceptable photos with very little graininess. Thus I allow the ISO to automatically adjust from a low of 200 to a high of 6400 to achieve proper exposure at the shutter speed and aperture that I manually set).
With the past volleyball tournament I shot, I found that I got more properly exposed photos by shooting a few photos using the above Auto ISO technique. After reviewing the ISO level automatically set by the camera with these photos, I manually set the ISO to that level at the shutter speed and aperture level previously set. I'm not sure why I achieve more properly exposed photos this way. My guess is that under some conditions the Auto ISO setting just isn't fast enough to attain a proper exposure all of the time.
