I’ve been experimenting shooting bursts with auto bracketing.
I have my D5 in manual mode. Aperture is locked at f/5.6 and shutter speed is locked at 1/250. I have Auto Bracket set to 3 frames, 1 f/stop difference. CL set to 6 fps. Auto ISO is on. Maximum ISO = 51000, and minimum shutter speed = 1/15. I shoot a burst of 3 frames. I expect that the camera will maintain aperture and shutter speed but will vary ISO. Not so. It maintains aperture and ISO but varies shutter speed: 1/250, 1/125, 1/500. ISO is always well below the 51000 limit. Does the same even if I set minimum shutter speed to 200.
However, if I go to aperture priority and set a minimum shutter speed, then the D5 will maintain the aperture and shutter speed and will bracket the ISO.
It’s not really a problem because aperture priority with a minimum shutter speed does what I need it to do. But it is puzzling, and I would love to understand why it performs that way. Any insight would be much appreciated.