macjohn is a neutral density filter on a DSLR with short exposures and small aperture enough to prevent damage to my camera? (scientificamerican.com)
«This shows that when a planet starts to cool down, this boundary, even though it's always there, becomes a significantly more profound density filter,» Jagoutz says. (sciencedaily.com)
I wouldn't have been able to do this without a neutral density filter since it was midday and extremely bright outside. (ordinarytraveler.com)