Why not to try see atoms by giant telescope?

there are 2 problems with doing this:

1. it is true that microscopes and telescopes both do essentially the same thing -- they magnify the viewed object.

but telescopes are designed to focus on large distant objects, while microscopes are designed to focus on small nearby objects.

it is not practical to make one instrument that does both with equal efficiency.

the lens sizes, as well as the distance between lenses, are much too different to make that possible.

2. even if it were possible to make a telescope function as a microscope, (or to simply use the best microscope at the highest magnification) it is still impossible to resolve images below a certain size.

at the highest usable magnification of transmitted light, point objects are seen as fuzzy discs surrounded by diffraction rings - called Airy disks - the resolving power of a light microscope is limited by its ability to distinguish between two closely spaced Airy disks.

at any magnification higher than this, adjacent structural details cannot be seen as distinct and separate.

the magnifying process itself is limited by natural diffraction of light, to objects of about .2 micrometers.

this limit cannot be exceeded, even with the best microscopes, because of diffraction.

to see anything smaller, you would have to use an electron microscope.