Testing the Smartphone Digital Microscope
The Digital Smartphone Microscope seemed like a really good idea. The video circulated last year. It looked like fun, which is of course the reason to do anything sciencey. If you clicky here you can watch the original video on YouTube.
I had a couple of middle school volunteers, Andrew and Daniel, working in my laboratory last semester. We took on building three Smartphone Digital Microscopes as a project. In short, it’s a couple of pieces of Plexiglas or Lexan with an adjustable bottom piece for focus. The magnifier/macro lens is cannibalized from a laser pointer. A lot of the parts came from the store where everything was $1.
This was a good project for the middle schoolers for several reasons. First, in a lab you often have to make what you need. You make or fake it because the real deal either doesn’t exist or because it’s too expensive. Second, any project like this teaches that any problem is solved iteratively. Try it, and if it doesn’t work, try something else. Third, it was the culmination of things I had them doing which kind of fell under the heading of Playing With Polarized Light.
Most of my work involves what I call IBS:Itty Bitty…Stuff. The most common tools of my trade are the petrographic microscope, micro-infrared spectroscopy, the electron microprobe, the SEM with EDA, or with Backscatter Electron imaging, and nowadays the Field Emission SEM or microprobe. The idea of a portable petrographic microscope was appealing, so I set Andrew and Daniel to watching the video and getting together some refinements. Then we built it.
Here’s a photomicrograph from my lab scope. An image with crossed polars has a polarizer below, then the thin section, then a polarizer above the section. The above polarizer is rotated 90° from the lower one. The thin section is rotated and the petrographer observes how polarized light interacts with the sample. So how do we build it?
The first refinement the guys came up with was to use the third bolt as part of the sample stage. The one in the video was simply too floppy. The second was to leave the lens in the tube in which it came. The video has you take the lens out, which like an invitation for a fumble and a lengthy crawl-around on the floor. In the picture above, I have one of each lens mounted, one in the tube and one removed from the tube.
One of my refinements was to add a rotating stage. Polarizing film (linear polarizing material for you aficianados) goes below the stage and above the lens.
- The focal distance is very short, so specimens have to get very close to the lens. The rotating sample stage actually helps with that. But the sweet spot for getting things in focus is rather small. If you have a thick nut on the bolt holding up the top layer, you might not be able to get close enough to focus.
- Middle school boys are over-rated in terms of their destructive powers in dismantling laser pointers.
- We skipped countersinking the holes for the bolt heads in the bottom of the stand (not my best idea). As a result, if you lean on the stand by accident, you can turn it over.
- Andrew knew more about using my Smartphone camera than I did, which was kind of embarrassing.
- Getting the rotating stage centered under the lens is very difficult.
- A cheap laser pointer lens doesn’t work very well. It distorts around the edge of the lens, called a vignette in photography. Perhaps a more expensive laser pointer would have a better lens, but that kind of defeats the purpose.
- A clip-on gooseneck light from the dollar store works well. The light source is not really needed, and a bright LED light from the dollar store is too strong. This rig actually works better outside.
- This has been rattling around the back of my SUV for a while and still works fine.
- The three-point focus mechanism actually lets you focus with the sample stage slanted, so you can zoom in on side features and not just the top of the specimen.
Getting a photo through the lens takes a lot of fiddling and practice. Not to be too mercenary, but I ran up to the Museum store and bought a couple of pieces of amber with insects to play with ($5 each). Here are some of the results:
You can see here how the lens vignettes around the edges. The brown mineral in the middle is a biotite with a gray apatite crystal in the middle. Dark material is volcanic glass. Black minerals are magnetite. Fish Canyon Tuff, Colorado, crossed polars image.
Many thanks to Andrew and Daniel for their help and for all the fun!