Bahtinov Mask Focusing Mask Fish Bone Plate Focus Slides for Telescopes Product Description: "Bahtinov masks take the guesswork out of focusing and even get over the seeing conditions as it is a mathematical type approach to the task.The best focus for your telescope quickly and easily. Suitable for use on all types of telescope - reflectors, rafractors, Dobsonians, Mak-Cas and SCTs. They are made from precision laser cut acrylic, which is stiff and long lasting. They will never be brittle in the cold, unlike some other masks which are made from normal plastics. The masks grip the telescope tube gently but firmly with three metal posts which have non-scratching silicon sleeves to protect you valued telescope surface. This prevents slippage, whilst allowing the mask to remaining perfectly central. Because of this 3-post mounting, the mask remains centered, whilst fitting a wider range of telescopes. They are made from 2mm thick laser cut acrylic and the securing screws are capped with soft plastic so that they do not damage your telescope.These Bahtinov masks are adjustable to fit a wide range of optical tubes, unlike masks which are only able to fit one telescope., depending on model, in aperture making them very versatile. Please be assured that these focusing masks will work excellently for both reflectors and refractors with whatever focal length. All you need to do is to measure your telescope tube size and choose the right size of the mask ( if you are not sure where to measure). " We have 10 sizes to choose from! SKU NominalSize Telescope tube min outer diameter(appr.) Telescope tube max inner diameter(appr.) Click On 90850 60mm-90mm 60mm 90mm Buy Now 90851 80mm-110mm 80mm 110mm Buy Now 90852 100mm-140mm 100mm 140mm Buy Now 90853 120mm-160mm 120mm 160mm Buy Now 90854 140mm-180mm 140mm 180mm Buy Now 90855 160mm-200mm 160mm 200mm Buy Now 90856 180mm-220mm 180mm 220mm Buy Now 90857 200mm-260mm 200mm 260mm Buy Now 90858 230mm-290mm 230mm 290mm Buy Now 90859 270mm-330mm 270mm 330mm Buy Now Package Include : 1 x Bahtinov Mask(for Outer Diameter from 60mm-90mm) Please Know : 1.When you buy it , you need to check your out-diameter of the tube .Not just the Objective lens diameter .Becasie you need to put the item one the tube. 2.if you don't know which size should to choose you can ask me before buy it , Thanks 3.The size is not the diameter of the item, pls check the measurement way . Note: Please allow 0-2mm error due to manual measurement. pls make sure you do not mind before you bid. Due to the difference between different monitors, the picture may not reflect the actual color of the item. Thank you! If you really care about these details, pls DO NOT order. Advantage 1. The Bahtinov Mask Made of Acrylic, Very thin and light weight so you wont upset the balance on your scope. 2. Masks now feature 3 holes which can be attached with 3 screws to prevent the mask from falling all the way to the ground 3. Perfect focusing for your CCD, DSLR or Webcam in seconds 4. 3 bolts with plastic cover allow the mask to be simply attached to any telescope 5. Acrylic material thickness: 2mm 6. Color: Black How to use it? 1. Place the Bahtinov Focus-Mask over the end of your telescope; then locate a bright star near your Note: Due to the light and screen setting difference, the item's color may be slightly different from the pictures. Please allow slight dimension difference due to different manual measurement. Sold by-YJL official store