Step Down Ring 42mm-40.5mm

The opposite of step-up rings are step-down rings, which essentially do the reverse: they enable you to adapt filter and lens accessories with smaller thread sizes to lenses with larger thread sizes. For example, they allow you to attach a 52mm filter to a lens with a 72mm thread size.

Step-down rings are not as widely used as step-up rings because, in most cases, the smaller filter sizes result in vignetting. The exception to this rule is when using lenses and filters designed for larger-format cameras (i.e. full-frame) on smaller-format cameras (i.e. APS-C and Micro Four Thirds). In these cases, the smaller image field will often negate any vignetting or image clipping.