Fig. 1. Optical Setup using UC2 Optical Building Blocks.

a The 4f-system divides Fourier-optical arrangements into functional units, where $f^{\prime }$ corresponds to the focal-lengths. BFP corresponds to the back focal plane (i.e. pupil plane). b The unit element (cube) acts as a base framework for any component which fits inside (lens, camera, Z-autofocusing mechanism, etc.). b A magnetic snap-fit mechanism connects the optical building blocks to a skeleton to realize mechanical stability and rapid-prototyping of a given optical setup. c An exemplary setup of a microscope for an ordinary smartphone (not shown) and an inexpensive objective as a combination of available modules. The cubes fit on the baseplate grid at 50 × 50 mm² design pitch (see Supplementary Notes 3).