Astronomers use a variety of gadgets threaded together for their equipment, using some standard thread sizes that don’t come with Fusion 360 by default. Recently I decided I would try to image the upcoming solar eclipse from Mexico using a flash spectroscopy technique – take the image of the Sun through a diffraction grating and try to capture the Sun’s various layers using the resulting spectra. An image taken in 2017 become the Astrophotography Picture of the Day (APOD):

The Flash Spectrum of the Sun
Image Credit & Copyright: Yujing Qin (University of Arizona)

To do this I’ll need to put a diffraction grating over the lens of the camera (or alternatively use a T-ring and 1.25″ nosepiece) so the image includes a 1st order spectrum of the eclipse, which you can see above.

To mount the filter, a StarAnalyzer 100 lines/mm grating I got from Field Tested Systems a few years ago needs to be mounted over the lens of my DSLR, so I designed an adapter using a 58mm thread for the camera lens, and a 1.25″ filter thread for the filter. To get these threads, I needed to load a couple of XML files into my Fusion 360 folder. Unfortunately, this must be done after each upgrade because the file path changes. The folder to load the image into is detailed in this post on the Autodesk website:

The two XML files needed can be downloaded below. Thanks to Todd Munro for the CameraFileMetricprofile file and Paul Gerlach for the AstroISOmetric file.

After a test print showed that the 1.25″ hold was too small and the overall diameter too big, I reduced the inner diameter by 2mm overall and increased the outer diameter by 2mm. When printing this out in ABS, I decreased the outer wall printing speed to 15mm/sec to get a smoother finish and removed the brim platform adhesion type since this is a large flat piece and the brim messes up the start of the threads.

I’ll update this post as I progress.

By Gord

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