Dear Jeremy,
The farthest planet I have seen in the solar system through a telescope is Saturn. I am not a planetary scientist, mind you, so the only time I see the planets through a telescope is when I go to a public facility, and look through a small, amateur class telescope. But I'll share a story with you.
When I was a graduate student at UCLA's Astronomy Department, I used to go oberving (use the telescope) at Lick Observatory in San Jose, California. At that time, the largest telescope available to the University of California on a dedicated basis was the 3-meter telescope at Lick. I was using it then, and Saturn was up at sunrise. Right after I finished observing my stars, I asked the night assistant (the person who operates the telescope) to point it to Saturn. I went right down where the light is focused before it hits the instrument I was using, and looked up the barrel/tube of the telescope - My God, what a sight! I saw Saturn as big as a big pizza, right above my head, rings and all. I was awed.
I also want to say that when astronomers use big facilities such as the Lick 3-meter telescope or the Keck telescope in Hawaii, we are not allowed to operate the telescope. The reason is that astronomers would most likely keep the telescope open even in close to rain situations or when the humidity is too high - in our eagerness to get the data. So, we only operate the instruments that detect our starlight, calibrate it, analyze the data we get from it using computers, and the like. The night assistant is the one who operates the telescope proper, namely, where it points, at the request of the astronomer. The night assistant also decides when it is safe for the telescope dome to be open in case of inclement weather.
Isabel Hawkins