What constitutes proper exposure depends on the photographer's visualization of the final image.
As usual when thinking about exposure in a DSLR, a good place to start is to expose to the right to produce the range of unclipped (and perhaps clipped) highlights consistent with your vision. Noise in the very dark portions -- i.e. Zone 0 of the Archer-Adams Zone syste -- of the scene can be eliminated by raising the black point when developing the RAW file in the computer.
###Example
The image was shot at ISO 12,800. Raising the black point eliminated most of the noise in the background so that only moderate denoising was required and the image could remain sharp.
Alternatively, standard HDR techniques are an option.
###Further reading on HDR
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