In The Legend of Zelda: Link's Awakening, Link can complete a trading quest for the Magnifying Lens. In order to complete it, Link must trade many different items to people all over Koholint Island. Certain parts of the trading quest must be completed in order for Link to advance in the game. While the rest of it is optional, the Magnifying Lens, while not technically required, makes traversing the Wind Fish's Egg much easier.
The Ribbon can be traded with Mini Bow-Wow who resides in Madam MeowMeow's house in north-western Mabe Village. The female Bow-Wow is always in the market for beautiful accessories and upon seeing Link's Ribbon, promptly offers to trade a can of Dog Food for it.
The can of Dog Food can be traded with Sale, who lives in the Banana hut on Toronbo Shores. A collector of canned goods, Sale will offer to trade a bunch of Bananas for Link's can of beefy Dog Food. Despite his earlier claims to be a collector, Sale quickly devours the Dog Food, can and all, as soon as the trade has been completed.
The bunch of Bananas is given to Kiki, who can be found to the west of the entrance to Kanalet Castle. Upon receiving the Bananas, Kiki calls his monkey friends, and together, they build a bridge to help Link cross the river. When they are done, they leave behind a Stick that Link can pick up. This trade cannot be completed if Bow-Wow is following Link
The Stick can be given to Tarin, who is trying to shake loose a Honeycomb from a tree in the Ukuku Prairie area. He uses the stick to prod at the Honeycomb, prompting the bees to exit their hive and attack Tarin in self-defense. After Tarin runs away, the Honeycomb falls from the tree, allowing Link to pick it up for himself.
The Pineapple can be traded with Papahl who, at one point, is stuck up on the Tal Tal Mountain Range. He is famished and cannot summon up the strength to return home. Upon seeing the Pineapple, he begs Link to give it to him. Papahl quickly scarfs down the Pineapple and his strength returns to him. As thanks, he gives Link the Hibiscus he had picked while hiking in the mountains.
The Hibiscus is given to Christine, the female goat that resides in Animal Village, as it is considered to be proper to present a lady with a flower whenever someone wishes to communicate with her. She is a secret admirer of Mr. Write; however, due to her physical appearance, she is afraid of meeting him in person. She asks Link to deliver a Letter to Mr. Write.
Link delivers the Letter to Mr. Write, who resides north-west of the Mysterious Woods. Mr. Write is overjoyed to see that someone has finally sent him a letter. As a reward, Mr. Write presents Link with a Broom.
In Mabe Village, Grandma Ulrira has lost her broom. She is overcome with enthusiasm upon seeing Link's newly obtained broom and begs him to give it to her. She gives Link a Fishing Hook that she had found while sweeping the beaches of the island.
The Fishing Hook is given to the Fisherman who can be found beneath the bridge to the south of Catfish's Maw. As his reward, the Fisherman promises to give Link the first thing he catches with this new fishing hook. After a strenuous battle, a Necklace (a Pink Bra in the Japanese version) is fished out of the sea.
With the Scale in hand, Link can move the mermaid statue, The Mourning Mermaid, situated south of Catfish's Maw. Inside, he finds the Magnifying Lens. The lens can be used to read the book Dark and Mysterious Secrets of Koholint Island in the Mabe Village Library, and thus, ascertain the proper way to make one's way through the interior of the Wind Fish's Egg.