K9 Optical Crystal Photography Prism Set Create the coolest lighting with the 4 Pack K9 Optical Crystal Photography Prism Set ($23, originally $33). It comes with a 55mm crystal ball, 50mm crystal cube, 50mm triangular prism, and 60mm optical pyramid. Image Source: amazon.com 4 Pack K9 Optical Crystal Photography Prism Set $23 from amazon.com Buy Now