My weird hobby as I mentioned is that I am designing cheap "art" lenses for my cameras (basically an equivalent of things like Lensbaby or the Lomography lenses) by adapting surplus optics (basic meniscus lenses and achromatic doublets) or DIY telescope eyepiece lenses, to focussing helicoids using 3D printed barrels; I have then used them for pictorialist-influenced shoots. It has sent me down all sorts of rabbit holes.

I am fitfully working on my own focussing mechanisms; I have had some success with multi-start helicoid threads but they are are a challenge in plastic, so I am currently working on a modestly-precise hybrid plastic and metal mechanism, and daydreaming about CNC-driven solutions in the future when I have the working space.

I am also contemplating a slightly more complex, faster aplanat/rapid rectilinear design but my knowledge of optics is just not good enough to select the right lenses, yet, so it may end up being bodged and only very roughly empirical; a "nice" result rather than an excellent one.

But then any precision of the result is not really the aim; cheap plastic meniscus lenses are as interesting in black and white as anything else.