Optical Focus

When you take photos, you need to focus.
So when I go out the night to do astrophotography, I also need to focus 🙃.

No need to say, my collected data is shit when I don’t do it properly. Shooting stars do not give room for mistakes, even tiny ones.

And I struggle so hard to focus with manual lenses for astro (the autofocus does not work in such darky situations! Thus, I shoot with 60s-90s lenses from the URSS with a 2015 camera; So no autofocus anyway).

One would say

“Leave the old stuff, buy a real tube, equatorial mount & motorized focuser stuff”. –Michmich

Yet, I’m not considering switching my 5kg backpack for a 25kg rolling case.

And this night, I discovered the Bahtinov mask!


The Bahtinov mask creates a diffraction pattern when put in front of a lens.

Source: Wikipedia

The super awesome thing about it is that the visual artifact tells you which direction you need to roll the focus ring to sharpen the picture.

I want one.

Making one

Pain in the ass; The filter is tricky. It mainly depends on the camera focal length. And it would be cool to have the correct diameter for lenses.

Won’t buy one, time to 3D print mine!

I love the open-source world. My 3D printer is fully open source. The Bahtinov might be. My first exploration led me straight to the marvelous thingiverse. And especially here: Bahtinov Mask For Samyang 135mm Lens ⬇️.

And just like that, I downloaded Openscad, forked the project & tweaked it.

OpenSCAD, the source code and the rendering

3D Printing

Like always, I struggle so hard to scale my prints when size matter (what are you thinking?). So I first print the object upside down to print the ring first, kill the print, check the diameter with my lens & adjust.

Took me six shots to get the expected inner diameter. Does my printer suck?

Asked for 75mm, got 74.65m. This is too tight 😐


I made my DIY Bahtinov mask in 4 hours, almost including this blog writing (nope at all).
OpenSCAD kinda blew my mind: code, variable, versioning; that’s promising! Blender will stick to arts.

I own a coffee to dakloifarwa for the openSCAD source code!

Hold on, this is an animated gif

You are still here? Bonus!

Let’s code my first real OpenSCAD code -> I need a lens cap!

I printed it with wood, so fancy.
Reach this print at thingiverse.