Back to #1347 - Neil deGrasse Tyson.
Why Does a Bigger Telescope Let You See Farther?
Telescopes today work on the same principle as when they were invented, only bigger. A bigger telescope is a bigger bucket for collecting light. The more light you get, the dimmer the object you can detect and the farther away the object you can see, which is how each new generation of large telescopes has deepened our view of the universe.