Reddit reviews Double Concave Lens Even Edges and Thickness - Ideal for Spinning Top - 75 mm Dia 20 cm FL
We found 1 Reddit comments about Double Concave Lens Even Edges and Thickness - Ideal for Spinning Top - 75 mm Dia 20 cm FL. Here are the top ones, ranked by their Reddit score.
Double Concave Lens75mm Diameter20cm Focal LengthSciencent High Quality Glass Lens
It's a concave optical lens from Amazon. They're quite cheap and work great!
From what I've seen, the two main focal lengths used are 15mm and 20mm but I can't remember off the top of my head which one is more shallow.