When it comes to 3D printed lenses, they usually suffer from some limitations that manufactured lenses do not. Two of those limitations specifically are the lack of a variable aperture that can be stopped down and focus adjustment. Some 3D printed lenses get around the focus issue by using a commercially available helicoid lens adapter. And to solve the aperture problem, they may have swappable inserts.
Well, this 163mm f/2.5 3D printed telephoto lens from Felix Steel at Pixels and Prisms features both a fully adjustable 12-blade diaphragm aperture (a first for full-frame 3D printed lenses) as well as a manual focusing mechanism that can lock in the fully extended or fully retracted positions. Aside from the glass, it’s 100% 3D printed and can be built for less than $15. It’s also open source.