William Optics Bahtinov focusing masks, sized by dew shield diameter from 75mm up to 308mm, plus the patented mask cover for the Takahashi FSQ-106. A Bahtinov mask clips over the front of the telescope and turns a bright star into a diffraction pattern — centre the middle spike and you are in focus.
Goods ship factory-sealed. Measure the outside diameter of your dew shield before ordering, or tell us your telescope and we'll confirm the size.
