(Tri) Bahtinov masks

Bahtinov masks help you to focus your telescope or normal camera with a telelens on stars. The star you focus on will split into streks which have to be centered on each other by focussing. Most common is the three streak version of which one is not centered. That one will shift accordingly to you focus action. Once all three cross in one point you have reached perfect focus.

This is the version for 'simple' cameras. Reseller is Lonely Speck in the USA.

The TriBahtinov is a special version that is able to do the shifting in three direction which makes it a simple way to collimate your telescope.

The TriBahtinov Mask by Satakagi.

Explanation on english Wikipedia.

Extensive explanation on Youtube by Cuiv The Lazy Geek.

Design you own mask.

Further specify your own design.