Fine 3D printed Bhantinov Mask

I’ve thought about printing a Bhantinov mask for some time as I’m getting into astrophotography, but most of the designs I saw had quite thick gratings and Bhantinov factors (focal length / grating period) of up to around 250.

Whilst most FDM 3d printers don’t do well with fine detail, the increased control you get in the slicing software makes it easier to queeze out more detail in specific cases.

To that end, I have managed to make a mask with a grating period of 0.8mm, which is pretty much at the limit of what’s theoretically possible with my 0.4 mm printer nozzle.

On my 900mm scope that equates to a Bhantinov factor of 1125, which is the highest one I’ve seen so far (although I haven’t done much digging). I’m not sure if it will be more useful, but this means it’s at least possible to make more usable masks for smaller scopes.

The challenges with this are getting the thin lines to break away with the rest of the print cleanly. This was only possible with a well tuned printer with active compensation for any warp in the bed (bed mesh levelling). Still, where there were defects on the PEI surface of my bed, a couple of strands broke.

If anyone’s interested I can share some CAD and additional details about how I achieved this. I look forward to trying this out as soon as I get the chance!