Bahtinov Mask Focusing Mask for Telescopes, CelticBird 230mm Telescope Focusing Mask for a Tube Outer Diameter from 225mm-275mm

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. Suit for telescopes which out diameter 225mm to 275mm. Masks feature 3 holes which can be attached with 3 screws to prevent the mask from slippage and allow it to remaining central. Suitable for use on all types of telescope - reflectors, rafractors, Dobsonians, Mak-Cas and SCTs. Light weight so you won't upset the balance on your scope.