Category Archives: Design

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.


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 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.


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!


Simulation Driven Design

Big data and advanced materials have been identified as two of the Eight Great Technologies highlighted by David Willetts MP. Combining these technologies, last year I wrote an article entitled “Engineering components that last…” which describes the use of computer models to predict the material behaviour, allowing the lives of critical components such as those in gas turbine aero-engines to be accurately evaluated.

Building on this, a good understanding of material behaviour and computational modelling can be used throughout the design process of innovative products. Early in the design of a product the specifications are not fixed and design changes can be readily accommodated. Using computer simulations at this stage allows radically different designs to be assessed, a process that can be sped up by using high performance computing (HPC). Using HPC, large computational problems can be solved quickly by splitting the models into many regions (domains) each being solved on individual CPUs. This allows design changes to complex structures such as car bodies to be evaluated prior to manufacture.

Using simulation driven design, computer simulations are incorporated into all aspects of the design process, allowing more design iterations to be assessed while reducing the number of actual physical prototypes required allowing better products to be designed faster at a lower cost.                               yaris