4 吋透射球面，F/1.5，1/20 波長

I was initially hesitant about the price, but after running it on the interferometer, the 4-inch aperture and 1/20 wave surface accuracy delivered exactly the clean fringes I needed. It's noticeably heavier than my older spheres, which actually helps with thermal stability during long measurement se

The 1/20 wave precision really does make a difference in my interferometry setup—fringes were noticeably cleaner right out of the box. Only minor gripe is the shipping box could have been sturdier for such a delicate component.

The 1/20 wave PV spec is what sold me, and it holds up in my setup—wavefront looks clean across the aperture. Only gripe is the 4-inch housing feels a bit heavy to mount, but the optical quality justifies the extra care.