Use welding glass as a 10 stops ND filter - DIY Photography | Diy photography, Time lapse photography, Glass
Homemade Neutral Density Filter - YouTube
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GoPro ND Filters and How to Make Them - Drone Nodes
How To Create a DIY Low-Cost Neutral Density Filter | Envato Tuts+
Try this DIY Neutral Density Filter for Long Exposure Photos