The difference between magnification and resolution.

Electron microscopes can magnify objects many times to a good resolution.

Magnification is how many times the image has been enlarged.

Resolution is how clear the picture is. If resolution is 1nm it means that if two objects are one nanometer or more apart the microscope will show them as two different objects; if they are any closer than that they will look like one object.

Waves are only affected by objects that are bigger than half of their length: so big wavelength will only get diffracted by a relatively big object in the way- think of the sea with massive waves- if you put a twig in front of it the water would not be disturbed, you would have to put a tree in front of it to make any difference.

A small wavelength will be diffracted by tiny objects in the way: so the ripples from a raindrop would be affected by a twig. Electrons have a very small wavelength and so are effected by tiny objects- this means that more detail shows up in an electron microscope where the waves have been disturbed than it does on a light microscope (with a bigger wavelength.)