Petrographic Microscope Home Kit for Smartphones

I expect this will be most useful for core undergraduate courses that teach how petrographic microscopes work, like Mineralogy and Petrology classes.

The skills and concepts required are minimal, and will depend on the optical mineralogy and petrology lessons being taught in a given class. This is best used for an introduction to how a petrographic microscope works for remote learning.

This is situated in my course as part of a sequence of mineralogy and petrology lab exercises. While motivated by the need to pivot to remote teaching and learning with no notice during the global coronavirus pandemic, this design could be useful for any appropriate remote teaching, distance learning, or homework lesson where students do not have access to classrooms but need to learn about microscopy.

Optical mineralogy and petrology, including basic optical properties of substances, anisotropy and double refraction, birefringence, and relief.

Connecting theoretical concepts about optical mineralogy to physical materials and tools.

The goals for this design are primarily skills based, in that students will learn to operate the basics of a microscope when they lack access to full technical instrumentation.

The material shared here is a set of design instructions for building a home microscope kit using basic home tools and supplies from a hardware store or basic online supply store. Some access to tools and supplies is necessary for this to work, but innovations and edits to the basic design are certainly possible when certain supplies are unavailable. This design was modified from an existing smartphone microscope design that is freely available online; here I have added a rotating stage and two polarizing filters, and modified the basic frame design to better support those changes.
Plans for Petrographic Microscope Home Kit (Acrobat (PDF) 11.3MB Nov16 20)

Instructors or technical support who aim to build one or more of these kits should use proper safety protection when operating power tools and using tools and hardware.

The working distance of the microscope lens is, unsurprisingly, quite small, making it tricky to manipulate a slide on the stage. In addition to the revised cuts suggested in the instructions, I recommend giving students a few small craft sticks they can use as tools to move the slide gently while viewing it.

Centering and focusing are fairly rough with this design, which should not be surprising for such a crude model. The plastic collimating lenses used also create quite a bit of distortion; they are not a true replacement for a high-quality pol objective lens! But you can generally get a good image in the center if the stage is well focused, and adjustments are usually minor once the microscope is set up and initially tuned. No matter what, any home microscope kit is going to be a little finicky because the parts are not professionally machined and tuned; the goal here is to offer students a chance to play around with microscope parts and see how they work through some basic exercises, not to fully replace experience with real technical instrumentation.

For another tip, if you are able to give students elongated mineral grains for a grain mount, they could also learn length-fast and length-slow and optic sign identification techniques. This requires purchasing a piece of wave retarder film (example: https://www.edmundoptics.com/f/polymer-retarder-film/14827/), cutting out a small square piece, and adding it to the top stage under the analyzer film in the correct orientation. I recommend taping the edges of the film to a small plate of plexiglass or long glass slide, and marking the slow direction for the students, i.e. creating a wave plate that is easier to handle than film.

Sometimes it is possible for instructors to send students home with oriented crystal mounts and/or thin sections, if they have enough supply. It also works well to send students home with a blank glass slide, a small envelope of cover slips, a bottle of glycerin and/or clove oil, and a mineral powder so they can learn to make and observe grain mounts. This would likely work best to demonstrate and practice relief, a Becke line, pleochroism, stage rotation, birefringence, and a few other basic concepts. It would also work to give students a very thin sheet of mica to place on the stage and directly observe its properties.

This depends on the exact lesson design for using the tool, but here are some ideas: students may be able to work on an activity where they make a mineral grain mount and observe basic optical properties, such as relief, Becke lines, and pleochroism and color. When the analyzer is added to the assembly, they could also observe interference colors and extinction, and calculate the thickness or birefringence. This can be written up as a lab activity and submitted for discussion, participation, or a grade.

The original smartphone microscope design kit instructions are located here: https://www.instructables.com/id/10-Smartphone-to-digital-microscope-conversion/