Using an old camera to make a microscope

My kid just turned 7. My wife and I generally look for toys that cultivate more creative interests, especially in science and math. We were looking at "toy" microscopes. A decent toy is perhaps $30-$40. Will magnify but lenses aren't great. At this price point, lenses are fixed.
Going up to $50-$60, you get a much better build - and lenses are replaceable, but not standard lab microscope lenses (RMS mount). Going up to $70 gets you an actual microscope, with metal body and RMS thread lenses. So, maybe the best both worlds is a real microscope, painted pink.  ¯\_(ツ)_/¯

While looking at these I got to thinking. I've just purchased the Sony A7. My wife took my last purchase - the Olympus E-M10, so the EP3 is my backup. My Olympus E-PL1 is just going to gather dust.

I decided to try taking this spare camera (its going for < $100 used at this time. KEH had it for $67) and mount it on a bellows using an adapter for a microscope lens - the same standard RMS lenses that would work on a regular microscope. This is all well and good, but I need a way to hold this up to a slide quite steady, and a way to light it from the back. So I mounted the bellows on video rails, with a couple blocks to hold microscope slides and another for a flashlight. I also experimented with lighting. Using a simple folded paper shroud and flash, images look very different compared to regular back-lighting.

The end result is better than I thought it would be. I did learn quite a bit about microscope lenses along the way.

Rather than a lens, a bellows is mounted on the camera. The bellows in this case is M42 (old pentax mount) so a M42 to RMS adapter is used to mount the microscope lens on the bellows. An M42 to Micro Four Thirds adapter lets this old bellows mount to the modern camera.
The bellows,, and a couple blocks are all on photo rails. A couple threaded rods holds the slides in place, and the other block holds a flashlight with built in lens. To diffuse the light and change the look of the image, a simple paper hood can be added to scatter the light from the flashlight and the flash. While not a standard microscopy lighting method, it is normal in photography.

Look closely on the leaf and you'll see stomata!

What's important here is the camera, extension tube/bellows, microscope lens, a way to hold the subject steady, and lighting.

Many people have a relatively modern camera capable of live view. This camera used is among the first cheap mirrorless cameras, the E-PL1. At the time of writing, this was seen for $67 on keh.com. The bellows set me back $30 at the time, but has risen over time. granted, there's many other means of getting the microscope lens mounted. M42 focusing tubes can also be used to vary the distance of the objective from the camera. Flashlights were 2 for $10. the flash is a generic amazon basic flash for $30. Lenses can be purchased used. A plan lens gives a flatter field and is better for these large sensors, though you can find "lot" sales with several lenses on ebay for quite cheap.

Bellows alternative:

Lens lots on ebay:

The point of the bellows or focusing tubes is to vary the magnification of the subject. The farther away the lens is from the camera, the closer the front of the lens can be to it, and larger the image is on the sensor. A fixed adapter from M42 to your camera's mount will work fine.

Focusing is achieved by racking the bellows forwards or away from the slide. Altering magnification by expanding/contracting the bellows also alters focus a little and can be used to fine-tune the focus.

I didn't make my own sildes for this, though the ant used was just stuck on some scotch tape. The box of slides was a generic set purchased online.