A word or three on microscopes: You need one to work on the micron scale obviously, but which one? Well, you don't want a one-piece USB microscope. These frankly lie about magnification. A factor of "300x" compares the view of the object unaided to the view through the eyepiece. Problem: USB microscopes have no eyepiece. So the magnification they quote is totally dependent on the size of your screen, and how much you zoom the app. There is a limit, of course, on the number of pixels in the microscope camera.

What you want to know is how many microns there are to a pixel on your screen. Manufacturers are reluctant to give that information. So try to get one that gives an image of a calibration slide or other known object. Knowing the resolution (typically it's a 5MP camera with about 2500 pixels across) you can calculate how many pixels go across a millimetre. To do micron scale work, you need 1,000 pixels per millimetre. This is not often found on one-piece USB microscopes.

This doesn't mean they are useless - a wider field of view is useful, they are easily positioned, and development work at 10 microns is a good starting point. However, for the fine stuff you'll probably need a "real" microscope. These can be fitted with a USB camera, but use the magnification optics of the actual microscope. I use one that has a real magnification of 500x and that lets me view microns.

Note that you will get a far better view looking through the eyepiece than you will using a USB camera on the microscope. Your retina has a much higher resolution than affordable image sensors.