Category Archives: How to guides

How to make a Bahtinov mask using a 3D printer

Unlike NASA engineers, not everyone has access to a laser-melting 3D printer to print their own metal telescope components. However, 3D printers for plastic are becoming affordable with some printers available for under £500. I doubt that a plastic telescope would work very well (plastic isn’t stiff enough to hold the optics in perfect alignment), yet accessories such as Bahtinov masks can be easily made by 3D printing and will be considerably studier than home-made cardboard ones.

What is a Bahtinov Mask?

A Bahtinov mask is used to accurately focus a telescope by producing a diffraction pattern that visibly changes with small deviations from optimum focus. They are particularly useful for astrophotography.

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How to make a Bahtinov mask?

First of all you need to generate a pattern for the mask. This is dependent on the focal length and aperture of the telescope so one size doesn’t fit all. Luckily there are tools available to draw these patterns for you based on the aperture and focal length of your scope. I used this great tool from astrojargen.net. This tool has lots of parameters to adjust but we only need to worry about the basics ones: focal length, aperture and edge thickness. Obviously the focal length and aperture are set to those of the relevant telescope. Make sure that the edge thickness allows for an overlap of more than 5mm around the outside of the tube (more if you want to add some foam for a snug fit). This tool gives you a pattern in the form of a scalable vector graphics (SVG) file so that you can print and cut-out your own focuser. Better still you can create a 3D geometry using CAD software. In order to do this, the SVG file must be converted to an AutoCAD DXF file using a graphics editor such as Inkscape. Once converted the DXF file can be imported into Solidworks as a sketch. I extruded the sketch by 4mm and added a 20mm deep flange around the edge, adding a few fillets to make the edges smooth.

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Once the geometry is created it can be exported as a STL file ready for 3D-printing. I used a MakerBot Replicator 2 (thanks Johnston Lab!) and I’m pretty happy with the result!

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