Peter A. Collin wrote:

I know thqt with a film camera I would try a trick called "reciprocity
failure". Basically, you use a slow shutter speed and a tight aperture.
The film is exposed for so long that the colors shift in a very
interesting way. Don't know if there is a digital analogy to that.

Reciprocity failure doesn't happen with digital cameras, but noise can
be a problem with long exposures.

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