Bahtinov mask for tubus with outer diameter 139 to 216 mm | Astrozap

In astrophotography, focusing well can make a lot of blurry shots, but on a screen it's hard to tell if a star is really sharp. This Bahtinov mask makes that visible with three light spikes.

The mask fits on a tube or dew cap with an outer diameter of 139 to 216 mm. Place it in front of the opening, point at a bright star and slowly turn the focus ring until the middle of the three spikes falls exactly between the other two. Then remove the mask.

Measure the outside of the front of your tube or fog cap, not the opening of the mirror or lens. With bright light telescopes for astrophotography Focusing precisely is even more important because the range of focus is very small there.

For thinner and thicker tubes there are the mask for 63 to 139 mm and the mask for 216 to 292 mm.