Today’s Question: I do very little bracketing and HDR [high dynamic range imaging]. I’m expecting to do some, and I seem to be brain dead about the difference between the two. Am I understanding correctly that taking the series of exposures is done exactly the same for bracketing and HDR, and that the only difference is what you do with the exposures later?
Tim’s Quick Answer: Yes, in general exposure bracketing and capturing a sequence for a high dynamic range (HDR) image would involve the same basic process in terms of the original captures. The difference is primarily your motivation and how you process the photos after the capture.
More Detail: Put simply, when capturing a sequence of images for an HDR result you will be using exposure bracketing. The key difference between HDR and “simple” exposure bracketing is that with exposure bracketing the aim is generally to achieve a single good exposure. When bracketing for HDR, the aim is to blend the exposures into a final image that presents greater dynamic range than the camera could capture with a single exposure. The HDR image can be assembled from the bracketed exposures using software such as Aurora HDR (https://timgrey.me/aurora2019), Photoshop, or Lightroom Classic CC)
Exposure bracketing is generally motivated by tricky lighting conditions, or a lack of confidence on the part of the photographer that they will be able to achieve an optimal exposure. You can capture bracketed exposures that are brighter and darker than what the camera’s meter suggests, with the idea being that if the “middle” exposure isn’t optimal, the brighter or darker image from the bracketed set will provide a good alternative.
With exposure bracketing you just need to be sure to bracket enough that one of the captures will provide a good exposure. For HDR you need to make sure you cover the full range of tonal values in the scene you are photographing.
Because of the differences in terms of motivation and final result for exposure bracketing versus HDR bracketing, in concept you could bracket with a narrower range of exposures for exposure bracketing than might be necessary for HDR bracketing. In reality, however, I would tend to take a conservative approach in either situation, so you are always confident you’ll have all of the exposures you need to achieve your photographic goal. You could always delete the “extra” exposures that result from such an approach.
When creating bracketed exposures for an HDR image, I will generally separate the exposures by two full stops, and capture five or seven exposures to ensure I cover the full range of the scene I am photographing. The number of exposures could vary depending on the specific conditions in terms of overall dynamic range.
When using exposure bracketing to compensate for a lack of confidence in exposure settings, I would generally separate the exposures by a single stop rather than two stops, and only capture three (or maybe five) total exposures.
So, there are some differences in how you might approach exposure bracketing versus HDR bracketing, but the overall concepts are the same. In both cases I would generally use your camera’s automatic exposure bracketing (AEB) feature to streamline your workflow, simply changing the settings based on the requirements of the current photographic situation.