I think one of the keys is to get a wide enough range between the lightest and the darkest bracket so the software has good data at the extremes to work with.
Hi Richard,
Correct. Using 1.3 stops as a maximum interval obviously increases the number of bracketed exposures to cover a given range compared to a 2 stop interval. One can of course also mix this with noise reduction software, which would allow to use larger increments, but noise reduction also risks losing a bit of resolution. Cameras with very low noise may be slightly more tolerant.
I arrived at the maximum interval of 1.3 stops after comparing a lot of image fusion results. I made a huge series of 1/3rd stop intervals (at ISO 100) of a high dynamic range scene (partly in the sun, partly in the shadow), and then compared all combinations. First fusing all 0.3 stops brackets, then all 0.6 stop brackets by leaving out every other image, then all 1.0 stop intervals by skipping 2 brackets, and so on. I then noticed that at certain smooth gradients it became obvious that the smoothness of the gradient was negatively impacted by a too large (>1.3 stops) interval.
When the steps get too large, it may also become harder to align the images before fusion. Alignment is necessary for handheld bracketed series, but may also be needed for longer focal length images. A single pixel offset of one or more of the images, can influence the resulting fusion.
I used to use Tufuse Pro (similar to Enfuse), but prefer SNS-HDR (also uses exposure fusion, not HDR merge) because of it's virtually halo free tone-mapping quality.
Cheers,
Bart