I sometimes shoot exposure-bracketed photos on my Sony NEX-5R, for exposure fusion in Photomatix.
I'm thinking of taking just two photos, at -3EV and +3EV, which are the maximum values of exposure compensation the camera allows. I think that there's no need to use a smaller separation, like 2 EV, and no need to take more than two photos. My reasoning is as follows:
This camera has a dynamic range of 13EV, which is much greater than the 6 EV separation between the +3EV and the -3EV photos. This means that there's 7 EV (13 - 6) overlap between the two images: The brightest 7 EV of pixels in the image captured at -3EV will be the same as the dimmest 7 EV of pixels in the image captured at +3EV. This is essentially redundant information. Taking more than two photos, or taking photos separated by < 3 EV means greater overlap, and more redundant information captured, which doesn't help.
Is this reasoning correct?
1) In low-light situations, a photo at +3 EV may take a long time to capture, like 30 seconds, which you may not want if a photo taken at +2 EV will do the job.
2) I'm aware that DxoMark calculates the dynamic range at base ISO. Assuming that the dynamic range is only 7EV rather than the 14EV DxoMark measures, that's still greater than the 6EV separation between a photo taken at -3EV and a photo taken at +3EV.