Adaptor ring is a camera lens accessory that screws onto the filter thread of a lens, allowing photographers to attach filter system holders or filters of different sizes. Some adaptor rings are designed to "step up" or "step down" from the lens's actual filter diameter, enabling the use of larger or smaller filters that would otherwise not fit. Adaptor rings are commonly used in landscape, portrait, and creative photography to expand the versatility of lenses, facilitate the use of neutral density, polarizing, or special effect filters, and provide greater flexibility in controlling exposure, reflections, and color effects.