I think you're underestimating it also. For example, micrometres capable of measuring imperceptible differences have existed for many centuries, same for manufacturing machines (lathes, mills) that can shape objects to imperceptible requirements.
Cameras probably just don't require such precision.
Depends on the camera.
I think if we combine both of your comments, we get a more clear picture of reality: we've had the ability to manufacture one instance of something with precision for a while, but not the ability to do so consistently, reliably, or quickly.
i.e. tolerances have shrunk dramatically over the past century or so, along with time needed to produce things with such low tolerances.
However, while that is generally true across the board, tolerances haven't all gotten to the same place! Materials involved, costs, time to build, and need for low tolerances still largely affect all of it, of course.
And for some things, individual variations are even considered desirable.
Humans are capable of detecting extremely small details with their fingertips[1] anecdotally, this can be trained if you use your finger tips for precision work a lot, you can easily feel things that you can't see without significant magnification.
Additionally, I would push back on "many centuries", the Machine age came about in the mid 19th century, so if were being generous, 300 years[2].
[1] https://www.sciencedaily.com/releases/2013/09/130916110853.h...
[2] https://archive.org/details/englishandameri01roegoog/page/n2...
[2] is cited on the wikipedia page for micrometer. Cool book though, might read it.
I recall some lenses from the era having their actual exact focal length inscribed inside since they weren’t exactly 50mm and the variance was 0.2mm or so.
Don’t even get me started on Soviet cameras.
Point of the story, the lens had some shims to get into the proper focal plane relative to the camera. The model in question doesn't have the best sharpness reputation, some people put it on the worst 10 list of Nikon lenses. The sample I had is sharp so (VR didn't engage until 28 mm). My theory now is tgat the lens is sharp, and the bad rep comes from compromises during manufacturing (Thailand instead of Japan, with all the corresponding issues of setting up high precision operations in a new site), and potentially sub-par QC. Not sure if other lenses have shims as well, I'm kind of not inclined to disassemble perfectly working samples just to find out.
So no, shims aren't per-se a bad sign but rather one of a certain calibration strategy. If those shims are everywere so, manufavturing quality propably isn't the best.
Oh, one word on 50 mm lenses. Those are among the fastes, sharpest lenses ever regardless of manufacturer. And dirt cheap compared to "pro" models. Seems to be quite well understood optics.
I do have two pre-AF Nikon lenses, and those are master pieces of precision mechanics, dating back to the late 70s and early 80s.