Neutral-density filter - Wikipedia

ND Filter: A Beginner's Guide to Neutral-Density Lens Filters

Pulfrich effect - Wikipedia

Graduated neutral-density filter - Wikipedia

Photomicrography - Filters for Color Photomicrography

Baader Neutral Density Filter (ND 0,6 / 0,9 / 1,8 / 3,0)

Lens Rentals

Neutral-density filter - Wikipedia

Graduated neutral-density filter - Wikipedia

Neutral Density Moon Filters - Eyepieces - Cloudy Nights