Bahtinov Mask 150-200mm

A Bahtinov Mask is a focusing aid. When fitted over a lens, it creates a 6 pronged diffraction pattern. As you adjust the focus, the middle spikes will move. When exactly in the middle, perfect focus has been achieved.

Tis mask is adjustable in size allowing fitting to telescopes with tube / dew sheilds from 150-200mm.