Today’s Question: What do you recommend for the number of brackets for HDR [high dynamic range] capture and the f stop interval?
Tim’s Quick Answer: The real answer here depends in large part on the specific lighting situation for the scene you’re photographing. But in most “typical” HDR scenarios you are generally safe with about five exposures separated by two stops each, perhaps using seven exposures to provide a little extra “insurance”.
More Detail: When it comes to an HDR capture versus a single exposure, it isn’t as simple as needing to bracket versus not. In some cases you might be able to accomplish your goals for a scene by simply adding one additional exposure that is one stop brighter than your initial exposure. In other cases you may need to capture many more exposures to cover the full range of tonal values present in the scene you are photographing.
Generally speaking, I find that the types of situations most photographers face when HDR becomes necessary can be captured with a total of three exposures separated by two stops each. Most cameras enable you to bracket a total of three exposures, so this is an approach just about any photographer can take if they prefer to use automatic exposure bracketing (rather than manually adjusting the exposure for each frame).
Many cameras now support five, seven, or nine exposures for automatic exposure bracketing. This provides you with greater latitude for two issues. First, it helps ensure you’ll be able to cover the full range of exposure values for a wider variety of scenarios. Second, it provides you with a little insurance for situations where you needed to apply some exposure compensation above and beyond the exposure bracketing.
For example, a basic automatic exposure bracketing situation might involve a shot at a minus two-stop exposure, a shot at an even exposure, and a shot at a plus two-stop exposure based on a meter reading for the scene. But a given situation might actually require a minus three-stop exposure, a minus one-stop exposure, and a plus one-stop exposure in order to properly cover the range of exposure values within the scene. Having a greater number of exposures provides some additional latitude to cover this type of situation.
If you’re using two-stop exposure increments (which is what I recommend using) for HDR, chances are that nine exposures will be more than you need the vast majority of the time, and even seven exposures are probably more than you’ll need much of the time. But I would rather have too many exposure options than not enough, so I tend to favor using seven exposures separated by two stops each.
As for the separation between exposures, there is no need to use one-stop increments for HDR capture. Two stops will provide all of the overlap that HDR software needs to assemble an excellent result.