AFAIK, the microscope was a truly revolutionary invention because it introduced a concept that no one had ever had before: that something could be tangible and real but simply too small to see.
But is this correct? The ancient Greeks speculated about atoms but I’m unaware if specific dimensions were ever attributed to them, or if they were simply considered infinitesmal abstractions. Did natural philosophers or anyone else recognize that something could be very, very small? More to the point was there anything to which they could attribute a specific very small size? I’m sort of wondering if people who polished gemstones and used ultrafine jeweler’s rouge were aware of the dimensions of the materials they were working with? If anyone noticed that it would take ten thousand strokes of an emory cloth to wear away an inch of stone, did they then make the connection that one stroke would leave the stone a ten-thousandth of an inch thinner?
The Greeks came up with the idea that matter could only be divided so far before you reached a point where it was impossible to divide it anymore. This roughly corresponds to the idea of fundamental building blocks but it says nothing about the size of these atoms or what they are composed of.
The existence of atoms was not a generally accepted fact in the ancient world; it was more of a thought experiment brought forward by a number of philosophers. They did not have any experimental results backing their theory, as science in the modern sense did not exist. To the vast majority of people, including philosophers, the question if matter was a continous substance that could be divided into ever smaller parts infinitely of if you’d finally arrive at “atoms,” i.e. particles that can’t be divided further, simply didn’t matter. I dounbt there were more specific speculations on the size of those atoms. I suppose most Greeks supposed that dust particles were really small, but did not bother to consider which smaller parts dust particles consist of.