Recently, JPL has invented and developed a miniature optical microscope, microscope-on-chip using micro-channel and solid state image sensors. It is lightweight, low-power, fast sped instrument, it has no image lens, does not need focus adjustment, and the total mass is less than 50g. A prototype has been built and demonstrated at JPL.
Yu Wang, Yu Wang,
"Miniature optical microscope without imaging lens", Proc. SPIE 3921, Optical Diagnostics of Living Cells III, (27 April 2000); doi: 10.1117/12.384211; https://doi.org/10.1117/12.384211