There is no limit to how far you can see, if the object is bright enough.

Your eyes can see individual stars that are up to 16,000 lightyears away. You can also see the diffuse glow of the galactic core, which is around 25,000 lightyears away. And on a dark night you can even spot the glow of the Andromeda galaxy, which is 2,500,000 lightyears away.

A telescope doesn't change how far you can see; it changes how faint of an object you can see. An object that is twice as far away has to be four times as bright for you to be able to see it. An object that is 10 times as far away has to be 100 times as bright for you to be able to see it. Telescopes collect light from a large area and focus it into a smaller area, allowing you to see objects that would ordinarily be too dim.