The cheap stereomicroscopes don't have "indirect reflected light" but it's not hard at all to add a ring illuminator or just arrange a flashlight or other led light that comes in from the side. I emulate darkfield using a side illuminator all the time. You can also replace the installed LED with an LED matrix (like the tiny one adafruit sells) and just illuminate the outermost ring of pixels, this will emulate dark field mask.

Cheap is relative, I guess. You can find a used stereo microscope on eBay for well under $100, maybe under $50. Building one out of a pair of binoculars is a classic but relatively advanced DIY project. I’m pretty sure there’s a detailed write up of one in either the old Edmund's optics books or Scientific American’s amateur scientist collections. Something like this: https://web.archive.org/web/20190123040421/http://www.funsci...

If you’re thinking of something like a metallurgical microscope, those are more involved and expensive, but again, eBay.

Bought mine at our local "biological" museum for about $150 (in Sweden where everything is a little more expensive). 20x/40x magnification, indirect or through slide illumination, solid construction.

The leds could be better and/or brighter but works for looking at stuff and for photography with a 3D printed phone holder on one of the ocular lenses.

This scope is nontrivial to build and run. I recommend buying a cheap stereoscope and spending more time enjoying looking at things before jumping to diy.

Many of the best cell phone sensors are off-the-shelf Sony sensors that individuals can buy in reasonable quality. The “magic” of cell phone cameras is the combination of these decent sensors, a lot of processing (that you don’t want), and really amazing lenses (that, in a microscope application, you’re replacing with your own — better to go microscope optics to focal plane than microscope optics to cell phone optics to focal plane). Certainly at the hobbiest level cell phone cameras are amazing, but I suspect even “advanced hobbiest” or whatever would prefer the same sensor in a C mount.

(Note I am an OpenFlexure Maintainer) Camera sensors are very rarely the limiting factor for a microscope unless you are in pretty exotic modes where speed, timing, or low light conditions are important. The key reason it is better often to use something like a Raspberry Pi camera than a phone is you know exactly what sensor you have and can design for it. Also there are benefits of not having the lens in front of it where you then need extra lenses to act as eyepieces to view a virtual image. But using the picamera and either using a microscope objective and a tube lens (or in the low cost version just the picamera lens and a spacer) we can get diffraction limited performance in a really small, light footprint. (More detail on the optics for nerds: https://build.openflexure.org/openflexure-microscope/v7.0.0-... )

However, the camera/sensor isn't the clever bit. The main benefit of OpenFlexure is the automated stage. The range of motion is small and the motion is slow so it really isn't the right microscope for looking at something like a bug leg. But if you want to take loads of high resolution images with a high powered objective and stitch them into a composite image (or take time-lapses automatically autofocusing regularly) we are considerably smaller, more affordable and more customisable than commercial alternatives. With lots of options for scripting.

As an example of what is possible, check out this multi-gigapixel composite image of a cervical smear, and the resolution when you zoom in: https://images.openflexure.org/cap_demo/viewer.html Note, this is collected with an experimental branch of the software (of course open source). We need to do some tidying and bugfixes before it is ready for release.

People have been mounting off the shelf cameras to microscopes since before digital cameras existed.

>But we noticed that if you took a cheap old school microscope and stuck an iPhone on the lens the resulting images were infinitely more crisp vivid and high-res

That's the core reason why the Foldscope is so popular. It really does work well.

Working now. https://openflexure.discourse.group/