Telescope

The telescope is an item Link's sister, Aryll, gives Link in the beginning of The Wind Waker as a birthday present. Although she says she will let him borrow it for one day only, he ends up keeping it for the remainder of the game. It is her most treasured possession.

It is with this telescope that Link notices Quill looking up at the sky at the giant Helmaroc King kidnapping the pirate Tetra, and it is also the only time the telescope is truly needed to advance in the game.

Kaleidoscope
The Kaleidoscope is the second item from the Phantom Hourglass Trading Sequence. When Link takes the Hero's New Clothes to The Hero on board the Traveler's Ship in the North Western Sea he will be given the Kaleidoscope, which he mistakes for a Telescope at first. The Kaleidoscope needs to be taken to the Ho Ho Tribe.

Trivia

 * Zuko, one of Tetra's pirates, also has a telescope, very much like the one Link gets from Aryll.
 * Pink "scout" Bokoblins out on the Great Sea have a similar form of telescope that they use as weapons. Strangely, enough if a pink Bokoblin picks up a weapon, it holds both its telescope and weapon in the same hand.
 * Old Man Ho Ho also has a kaleidoscope which looks similar to the telescope from the outside.