Bahtinov Mask 67mm

thingiverse

This is a Bahtinov mask designed specifically for the Sony SEL70350G but it should work on other lenses with 67mm filter threads, ~350mm focal length and ~f6.3 focal ratio.This does not screw into the filter threads but just fits inside with a slight overhang to prevent it from touching the glass of the lens. In testing I found that it sat snugly and did not fall out. It would be used with the camera pointing up anyway so it doesn't need threads.The point in the middle is to make it easy to fit and remove the mask when the lens shroud is fitted.A Bahtinov mask is a tool used to achieve perfect focus in astrophotography, once fitted over the lens a pattern of diffraction spikes forms around bright lights. You look for a bright star then adjust the focus until the diffraction spikes cross centrally.It is very difficult to achieve a perfect infinity focus point without either one of these masks or software.