MK-N-AF1-B Macro Extension Tube Set Supports accurate Autofocus. Combined with 3 tubes in different length: 12mm, 20mm, 36mm, tubes may be combined for greater magnifications. Features: Support accurate Autofocus. Built-in electric pins. Combined with 3 tubes in different length: 12mm, 20mm, 36mm, tubes may be combined for greater magnifications. Made of high-quality ABS that is more strong. Upgraded circuitry to work better with digital SLRs cameras and SLR lenses. Superior lock pin which can tighten the tube joint. Perfect for macro shooting.