The Explore Scientific 2" Adapter for the FFFR507X-00 (3-inch 0.7X Field Flattener/Focal Reducer) is a crucial accessory that allows users to connect the larger 3-inch reducer/flattener to optical tubes equipped with a standard 2-inch focuser. This adapter is primarily praised for its functionality in enabling the use of the field flattener/focal reducer, which significantly improves image quality (especially for astrophotography by correcting field curvature and reducing focal ratio for wider fields and shorter exposure times). Newer versions of the adapter also include threading for 2-inch filters, addressing an earlier omission. While effective and essential for specific setups, a recurring concern among users is its relatively high price for a small adapter, with some feeling it should ideally be included with the reducer/flattener unit itself. It's generally a well-regarded piece for its intended purpose.