Zoom Lenses can be purchased at the Prize Exchange in Veilstone City. Each one costs 1000 Coins, and you can either win coins or buy them from the Veilstone Game Corner.
There are no other ways to obtain a Zoom Lens in the game.
The Zoom Lens is a Hold Item that boosts the accuracy of the holder’s moves by 20%, but only if its opponent acts first.
Zoom Lens Location
The Zoom Lens is found in the Veilstone City Prize Exchange building, next door to the Game Corner, on a raised strip to the south of the Pokémon Center.
To reach it from the Pokémon Center, head south on the main paved street.
Take the first staircase you see, and the blue-roofed Prize Exchange building will be right in front of you.
Speak to the clerk in the booth, and find the Zoom Lens listing at the very top.
Each Zoom Lens costs 1000 Coins, which are obtained at the Game Corner next door. You’ll get them by winning coins from the slot machines or by buying them from the clerk using PokéDollars.
The PokéDollar-to-Coin exchange rate is 1000 for 50 (or 10000 for 500). So to buy enough Coins for a Zoom Lens, it would cost 20000₽.
There is no limit to how many Zoom Lenses you can buy.
What Does the Zoom Lens Do?
The Zoom Lens is a Hold Item that boosts the holder’s accuracy during a move by 20% if the opponent has already acted in that turn.
If you give this to a slow Pokémon whose moves are slightly less accurate than normal (Rock-type Pokémon and moves often fit these descriptions), the Zoom Lens can help get an extra hit or two in during a battle.
Otherwise, Wide Lenses are usually the more appropriate option. A Wide Lens boosts the holder’s moves by only 10%, but has no drawbacks like the Zoom Lens does.