This is really not a problem that’s fixed by open source.
The microscope will be controlled by a card that only plugs into 30 year old desktops. If you open source the drivers for it this only gives you the source code to drivers for Windows 95. These drivers will be incredibly hacky and hard coded and probably die if you install a service pack.
Having access to the source code doesn’t let you replace the entire stack because you’re still physically tied to old hardware, that is worse than a raspberry pi and even just making sure that you can update Windows is a feat of engineering.