How many bracketed exposures does a high contrast scene need?
Enter the dynamic range of the scene, or two metered shutter speeds, and the range your camera handles in one frame. The calculator gives the number of frames, the EV offsets and the shutter speeds.
How the tool works
The number of frames is ceil((scene range – camera range) / step) + 1, with a minimum of 1. For a 12 stop scene, a camera that handles 9 stops in one frame and a 2 EV step, that is ceil(1.5) + 1 = 3 frames at -2, 0 and +2 EV. The frames are centred on the middle exposure, and the shutter speed for each is the base shutter speed multiplied by 2 to the power of the offset.
If you meter the shadows and the highlights at the same aperture and ISO, the scene range is log2(shadow shutter time / highlight shutter time). The middle exposure is then the geometric mean of the two times. The table shows the exact value and the nearest third-stop setting. Frames longer than 30 s are flagged because you will need bulb mode.
This is a planning estimate. The usable range of a frame depends on the camera, the ISO and how much shadow noise you accept. Use a tripod, a fixed aperture and a fixed ISO, and change only the shutter speed. Moving water, clouds or people can ghost between frames. A 2 EV step is a common choice for merging in Lightroom HDR Merge. Many cameras limit auto bracketing to 3, 5, 7 or 9 frames, so check your manual.
Questions
How many bracketed shots do I need?
Divide the extra range your scene has over one frame by the bracket step, round up and add one. The tool does this for you.
What bracket step should I use?
A 2 EV step is a common choice for merging in Lightroom HDR Merge. A 1 EV step gives smoother merges but needs more frames.
What if a frame needs more than 30 seconds?
Most cameras stop at 30 s in timed modes. Use bulb mode with a remote release, or raise the ISO or open the aperture.
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