Here's one for the guys out there with outsized, egg-shaped heads:
Is there such an animal as an optical ND filter with a nonlinear response, brightness-wise? I.e., something that would attenuate highlights, while leaving mids / shadows alone (or attenuating them less)?
I'm guessing no (though a pola is a similar thing, I suppose) - but it's an interesting thought exercise. (It should be obvious where this came from - compressing dynamic range, etc.)