Multiple Magnification Glass Bead Microscope

This was inspired by the [designs by Pacific Northwest Laboratories](https://availabletechnologies.pnnl.gov/technology.asp?id=393), using a glass bead to magnify samples that are then imaged on a smartphone. However, after using it for several short lessons and demonstrations, I wanted to improve some areas of their design.

This design has several improvements:
* Multiple magnifications that can be easily switched
* Ability to move samples easily
* Use of the higher resolution rear camera
* Optional USB LED lighting and optics system

This design uses a 0.5 mm, 1.0 mm, and 3.5 mm beads, which have a magnification of about 500X, 350X, and 100X respectively. Using digital zoom on the camera will allow even higher magnification.

It works great with prepared slides, where some slides look best at high magnification and some look best at low magnification, but can also be used to look at fresh samples.