The basic Community Microscope is great for looking at really tiny things - like, 10-100 microns in size. But #microplastics such as collected with a trawl like #babylegs are a bit bigger -- between a grain of sand and a grain of rice.
For these, we need 2 things:
- a lower magnification microscope
- one that lights the sample from the same side as the camera - "front lighting"
I'm building on the notes and brainstorming in this question: https://publiclab.org/questions/jiteovien/08-08-2018/can-the-community-microscope-analyze-ocean-microplastics
There is also an activity on analyzing microplastics: here: https://publiclab.org/questions/maxliboiron/07-19-2018/how-to-analyze-plastics-forensically
Differences from other microscopesOur basic microscope design has the lighting opposite the sample, so it's back-lit. This design will primarily front-light the samples, and look down on them from above, like in this diagram by @jiteovien:
Note that @maxliboiron has said a second light source from below is good; I think there are some ways to do this since our stage is usually a plexiglas sheet, but in this example i'm sticking to lighting from above.
Adapting the Community Microscope
Next, follow these steps to modify your webcam.
Note that even if you have already built your Community Microscope Kit, you can flip the lens and "go back" to this dissecting scope design.
Unscrew the small screws behind your webcam (you can skip this if you've already flipped your lens - we just need to get the silver cover off of the lens):
Now, pull off the silver cover - it's just pressed on, no unscrewing needed!
Now, partially unscrew the lens -- I believe it's approximately 2 rotations.
To test the focus, hold the camera about 1 cm away from something tiny - fine print on a dollar bill, a bit of dust, etc -- and adjust the focus a bit so you have it generally in focus. Don't worry, we can adjust this more later. Here's a bit of microplastic debris:
Now close up the webcam again.
Back to your microscope stage (that you built using the instructions linked above), you'll need a white backdrop; I used a white Post-it, but paper will work fine.
Then add 2 rolled-up pieces of tape on either side of the circular hole on the top plate:
Place your webcam so it looks down through the circular hole, towards the white sheet of paper.
Now you'll have to lower the stage quite a bit. I ended up about 2 cm from the paper, with the lens 1 cm from the paper. Now you can rotate the lens to make finer adjustments, but raising and lowering the stage will also affect focus. Try adjusting both until you can see really fine details -- i used the fine print on a subway card as a reference:
Here's a driver's license:
OK, you're done! I found that the webcam in our kits is sensitive enough that not a lot of extra light beyond ambient light is needed, but it probably depends on what you're looking at.
I'd love to see how people try back-lighting as well! And happy to take any feedback or refinements in the comments below. And -- share photos of your builds please!