I've been shooting with my sony a7r2 and I've started using the Smooth Reflection app. The app averages a series of shots (from 2 to 1024 I think) to replicate the effect of an ND filter and produces a single RAW file in camera. As an ND filter, I love the application because it gives me infinite variability and removes issues of color cast, flare, vignetting. Basically it is an (almost) perfect ND.
Of course the averaging process also reduces the noise. So I'm wondering how much extra dynamic range can you get from averaging shots? Does it basically increase as log_2 (sqrt(n))? So 4 shots is 1 extra stop, 8 shots is 1.5 stops?
I suppose if noise were IID you could average it out of existence so then I'd be limited by the A/D (14bits in my body?).
From an efficiency standpoint, averaging is probably not as effective as bracketing with different exposure values. But averaging with the app has practical advantages like: (1) produces a single RAW file, (2) movement appears natural since all the exposures are the same and I don't need to mask/deghost motion, (3) I can avoid layers blending in PS or using HDR merge.
I'm actually very happy with the single shot performance of my sensor. I'm just exploring alternative ways of working and the SR app makes it easy to average with almost no workflow penalty.