Why do you list a range of thickness values for each of your opal diffusers?

Because of the technique used in the fabrication of opal diffusers, the opal coating layer is subject to some variations. While the typical opal layer is 0.45mm thick, the thickness of this layer can vary anywhere between -0.2 and +0.35, giving the opal layer a possible thickness between 0.25 and 0.8mm. Due to the limitations in the manufacturing process, it is not possible to get a tighter thickness tolerance. The variation in the coating tolerance then results in a variation of the total filter thickness.