A variable neutral density filter filters the amount of light coming into the camera, making long exposures, depth of field, and other effects easier to do. They can usually be pretty expensive ...

Many observers use either neutral density filters or variable polarizing filters to reduce the Moon’s light. I prefer the latter because an observer can change how much light the filter transmits.

Using a polarizing filter, the research team, which included Robert Antonucci and Omer Blaes, professors of physics at the University of California, Santa Barbara, isolated the light emitted by ...