In order to investigate the resolution of the Foldscope when paired to my particular phone (an LG G4), I seeded a slide with 45 micron and 6 micron polystrene beads. Below are images taken in dark field (top) and bright field (bottom). The 140x lens has a theoretical resolution of about 2 microns, so, expectedly, I was able to resolve the beads just fine. I noticed an odd effect present in the dark field image but absent in the bright field. Namely, the 45 micron beads were acting as microlenses in tthe dark field image. Curiously, this effect is absent in bright field. I wonder if I can create a microlens array out of these larger beads if I can form a mono-layer of them (if money were not an object… these beads are pretty expensive).

As a bonus, here are dark and bright field images of just the 6 micron beads in high magnification. The high mag lens was much more finicky, but we can see individual beads clearly.