Adaptor rings fit into the lens to accommodate the filter holder. Once the adaptor is in place the filter holder clips firmly to it using a smooth, quick-release, spring-loaded mechanism. Sturdily constructed with an aluminium screw thread, the adaptors are available in both standard and wide-angle configurations. Special sizes can be made to order. The wide-angle adaptors are designed so that the filter is placed as close as possible to the front element of the camera lens, and should be used to prevent vignetting with wide angle lenses.