Related cool diy-ish optical stuff...
A friend sent me this simple design for a raman spectrometer [1].
And some 3D-printable cage optics for when alignment is really important [2].
[1]: https://hackteria.org/wiki/images/a/a0/MobPhone_RamanSpec_20...
[2]: https://www.sciencedirect.com/science/article/pii/S246806721...