You can use M42 screw mount lenses, such as or 42mm screw mount lenses, and even enlarger lenses. The length of this Helicoid tube is 25mm (min) to 55mm (max),it offers a total of 30mm movement distance for the lens focusing. This Helicoid tube is useful for those lenses without focus ring, Tube offers fine focus control for macro photography. This focusing helicoid tube is made with 42mm front mount and standard 42mm rear mount and is made with light-weight alloy. It could be used as Macro Barrel. Automatic diaphragm, auto-focusing will not operate correctly while using this adapter. Manual focusing with mode metering is ok with the adapter. Instruction:Attach the Helicoid tube to the lens,then mount the combination of lens and Helicoid tube to the camera. This listing is for Adjustable Focausing Helicoid M42 to M42 12mm-17mm lens adapter. Automatic diaphragm, auto-focusing will not operate correctly while using this adapter.Manual focusing with mode metering is ok with the adapter. Color: Black Material: Aluminum alloy Package Contents: 2 x adapter Only the above package content, other products are not included. Note: Light and different displays may cause the color of the item in the picture a little different from the real thing. The measurement allowed error is +/- 1-3cm. This tube useful for lens without focusing ring. And it can be use as macro extension tube. There is no electronic elements in the adapter. aperture and focusing must be manually control. 2pcs adapter: 1pcs M42 To M42 25-55Mm & 1pcs M42 To M42 12 - 17Mm The all-metal adapter is designed to fit the lens securely, yet can still be removed easily when not M42 to M42 Mount Lens Adjustable Focusing Helicoid Macro Tube Adapter - 25mm to 55mm The length of this tube is 12mm(min) to 17mm(max),it offers a total of 5mm movement distance for the lens focusing.