Here is a USB microscope i made quite a few years back. Its very very simple to build and in its simplest form all you need is a USB webcam.
Basically you just remove the lens and turn it around then TADA! you're done. This is not my idea and i read it somewhere online but i really can't remember where i read it.
There are two parts to this instructable, 1st is to make the microscope from the webcam and 2nd is to make the frame or microscope body
(more info in picture annotations of each step)
Step 1: The Microscope
Firstly we need a USB webcam, try to get one where you can screw the lens off no need for any fancy high resolution ones although it might work better. I have no idea what make or model mine is as its just the cheapest one i could find at a local computer store.
Now carefully remove the lens and place it back "the wrong way"and thats it!
-To remove the lens you should be able to just unscrew it out, but to put it back in backwards you might need to open up the casing.
-You can test if it works by trying to focus it by hand to look at your monitor, you should be able to see the individual pixels
Step 2: The Frame
Here I made a frame/body for it using Lego, of course you may use any other method and materials that you like.
For my design, i first assembled some parts around the webcam that can secure it firmly, I then built around that.
1 important point to note is that i used a worm-gear to adjust the focus, this is because it allows precise control and will only allow 1 direction of transmission (you can turn the worm-gear to move the assembly up and down but not the other way)
Step 3: Usage and Some Pictures
Using the USB microscope is quite straightforward. just plug it into a computer and run any software to view the webcam (even skype will do). place the sample under the lens and focus. You can prepare samples as you would with a conventional optical microscope or you can just place any object you want to view under the lens. Please remember to properly illuminate your samples, you can shine light on it or from below it, but not too bright.
Thanks for reading, please let me know if you have suggestions or if there are any mistakes or questions
and if you like please vote thank you ^^