Originally posted by Arachnophilia:
without changing the shutter speed to match? |
You want to shoot at different exposure levels, so you'd want things to be different. You could bracket by changing aperture, by changing shutter speed or by changing ISO (as some newer DSLRs allow automatically) but the point is you want to shoot at different effective exposures. So you wouldn't change the aperture one way and the shutter the other way or you'd end up shooting at the same exposure.
Bracketing is useful when the lighting is changing quickly or you aren't really sure which exposure to shoot at, particularly if it is a 'one off' type opportunity. Normally it allows you to shoot at (for example) -1 EV, 0 and +1EV around where the camera meter has decided is the 'correct' exposure. You can shift this by using exposure compensation in the first place, so if you'd decided to deliberately underexpose from the meter reading by 1 stop, and were bracketing +1 and -1 stop, you'd shoot at -2, -1 and 0 EV around the metered exposure reading.
Usually you can change the bracketing amount between 1/2 a stop and 2 stops around the metered exposure.
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