Item Type: Focal Length Extension Tube Kit Material: Aluminum Alloy Gross Weight: 107g / 3.8oz Extension Tube Height: Approx.3mm / 0.1in, Approx.5mm / 0.2in, Approx.7mm / 0.3in, Approx.10mm / 0.4in, Approx.12mm / 0.5in, Approx.15mm / 0.6in, Approx.20mm / 0.8in, Approx.30mm / 1.2in Thread: M48X0.75 Use: for Astronomical Telescope Photography Package List 8 x Extending Ring 1Focusing Problem Elimination: The extension tube has M48 female thread and M48 male thread, which is used to solve the spacing problem in astrophotography and eliminate a series of focusing problems. 2Eliminate Redundant Light: The design of female thread can eliminate stray light and reflected light, making the image clearer and more perfect. 3Variable Combination: The required spacing can be achieved by combining several extension rings of different lengths, you can use 1, 2, 3 or 8 extension rings as required. 4Type: Astronomic telescope M48 threaded extension tube, the height of the extension tube is 3mm, 5mm, 7mm, 10mm, 12mm, 15mm, 20mm and 30mm. 5Aluminum Alloy Material: All metal structure and anodized aluminum process, durable, using this extension tube can obtain the correct image scale or the precise spacing required by the reducer or field flattener.