Early on in Pokemon Sun or Moon you get the ability to take and submit photos with the Rotom Dex, each photo you submit earns you points which can upgrade the Poke Finder's version once you hit a milestone. Here are the number of points needed to unlock each upgrade.

Unlockable	How to Unlock
Version 2 - Unlock Zoom function	Reach at least 1,500 points.
Version 3 - Zoom upgrade	Reach at least 10,000 points.
Version 4 - Final Zoom upgrade	Reach at least 100,000 points.
Version 5 - Unlocks option to call pokemon to you	Reach at least 1,500,000 points.