Sorry, can't tell you that, I let the microbiologists do it for me. They were very possessive about their instruments, like I was with mine. So... how are you doing it? I bought a $29 microscope from China last week to look at the backside of leaves we thought were infected with bindweed mites. Saw circular yellow and red spots on leaves that looked to the naked eye, to have white powdery residue. Under a scope, it's a whole different world.

For normal brightfield microscopy industrial cameras are very good (the internal sensor chipset is the important component, and there are only a few manufacturers globally) and usually offer both USB UVC and HDMI output. Monocular optics are very cheap and offer free-zoom (so-called 'zoomtube', great for video) and configurable magnification.

In terms of reflected light microscopy, you are going to get very good results with off the shelf ~$100 systems (camera+monocular zoomtube) and LED ring lighting (preferably anti-glare with configurable polarized filters).

You get a solid upgrade switching to transmitted light microscopy. This requires some sort of transparent stage with underside lighting. This can be as simple as placing an unprepared sample on a slide and shining any light (like a phone LED) through it. But it works better if the light is even, the light is collimated, the light is focused, the light is controllable (ie. light source + collimator lens + condenser, at precise relative distances).

At high magnifications the focal plane is very thin. You will need focus stacking for many unprocessed specimens, which can be achieved in software but requires a rigid platform and a steady hand.

Around this level you get some good upgrades from taking thin sections with a razorblade. You can buy mini microtomes but they're basically razorblades. Just buy razorblades. Staining also helps, read for example http://digitalcommons.mtu.edu/cgi/viewcontent.cgi?article=11...

If you are serious about your images, you can buy a cheap calibration tool for measurement purposes and synchronize it to software for markup and addition of digital scale purposes.

Beyond these you certainly need a rigid platform. To this point things are quite cheap, depending upon your requirements you could be only $200 in and happy with a range of stains, thin sections, configurable lighting, aperture, precision movable stage, etc.

Once you're in this territory you probably want a better turret and oil objectives. This is expensive.

Motorized stages, focus, filters/polarization, etc. are all options, often hard to retrofit to existing scopes, but of great utility depending upon what you're looking to achieve. I am sort of designing around this area. I am interested in structured light microscopy, which has recently been achieved for 10K EUR by academics in Europe. I may offer something cheaper if I can get it working.

Beyond that the next steps are precision methods like darkfield, phase contrast, DIC, fluorescence, etc. These get expensive quickly, requiring additional matched hardware and dedicated objectives. I know little about these techniques yet.