My Mattel View-Master VR headset was the last out of four phone-based VR headsets I retired and intended to take apart. I have one more that I'm going to spare this round of teardown:

I disassembled those four headsets to see four different variations on the Google Cardboard concept. This BB-8 themed unit is an actual Google Cardboard made of cardboard. Except for the lenses, naturally, which will eventually be harvested as I did the other four.

When researching in preparation for this teardown series, I read up on Google's specification for Cardboard lenses. I had expected all of those headsets to have identical lenses, but I was wrong. These four headsets had four distinctly different lenses with different diameters and thicknesses. I salvaged them without a clear idea of what I would do with them. I think eight identical lenses would have some interesting possibilities, certainly more than four pairs of distinctly different designs which is what I have on hand now.

I don't know enough about optics to compare similarities vs. differences of optical characteristics of these four lenses. But I know they do fundamentally similar things. These headsets place a phone screen close to our face, far closer than we can comfortably focus our eyes without presence of these lenses. Putting the phone close also lets the screen fill our field of vision. What can such a lens be repurposed for?

My first tentative idea is to build a small loupe out of one of these lenses, giving me a workbench tool to inspect details in teardowns. A quick test just by holding it up to my eye seems to support this idea. The next idea was to see if I can build it into a magnifying ("macro") lens for my phone camera. A quick test worked only to a very limited extent. I see a few magnified details within a tiny cone of clarity in the center of the camera's field of view, leaving the rest of the image unusable. I need to learn more about optics before I can diagnose what went wrong with that idea. In the meantime, I return to tearing down stuff I do understand.