Alstar Bahtinov Mask Focusing for Telescopes FM180mm a Tube Outer Diameter (OD) from 195mm 240mm

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 They are made from 2 mm thick laser cut abs; Securing screws are capped with soft plastic so they do not damage your telescope; These Bahtinov masks are adjustable to fit a wide range of optical tubes; They have adjustment latitude of about 195 to 240 mm The masks grip the telescope tube gently but firmly with three metal posts which have non scratching silicon sleeves; protect you valued telescope surface; Prevents slippage; Allow the mask to remaining perfectly central because of this 3 post mounting Suitable for use on all types of telescope; They are made from precision laser cut enforced plexiglass which is stiff and long lasting; They will never be brittle in the cold unlike some other masks which are made of normal plastics 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