My Twitter feed has recently been atwitter with discussions of cheap cardboard microscopes, for example this one. This reminded me of an older discussion of building a microscope using only a laser pointer lens and a smartphone. One example can be found here, but there are many others. I decided to experiment with this. I found an old laser pointer and pulled out the lens.
Constructing a microscope is a lot easier than the videos suggest. All you really have to do is place the phone on a flat surface and put the lens on top of the front lens of the phone camera. To the right is an image I took of a dragonfly's wing (thanks to my daughter, who supplied the subject.
The next step was to build a DIY polarizing microscope. This required two polarizers (I have a LOT of these lying around, being a polarized light geek), a light source (LED) and lens+phone assembly. The hardest bit was getting the sample (in this case adipic acid) at the correct focal length. All of this was done in the space of maybe 20 minutes.