Bahtinov focus mask for Sigma 150-500 zoom lens

thingiverse

This is a focusing aid used for astrophotography. This particular one is made specifically for use with a particular zoom lens, the Sigma 150-500 APO DG OS used at full focal length. The mask fits into the lens hood - it just slots in. It helps you accurately focus your lens by mounting it in front of the lens and pointing the camera at a bright star. You then see a particular patern in the viewfinder or liveview and adjust the focus manually untill the pattern is symmetrical. Once you have achieved that you remove the mask and the camera is ready for shooting. Its use is described in more detail in this wikipedia article:http://en.wikipedia.org/wiki/Bahtinov_mask Credits go to the creator of this website:http://astrojargon.net/MaskGenerator.aspx It is the calculator there that created the correct pattern - I then just extruded it into three dimensions. Instructions Just print in black ABS. Scale down to one tenth size in the slicer before printing. Be careful when peeling it off the build plate as it breaks quite easily. The slots may need some trimming.