You can zoom puzzles in on the high levels of difficulty. The availability of this option depends on the size of your device and the level of difficulty you choose. You will see a magnifying glass button in the game menu, if the option is available.
After you tap on the magnifying glass button the screen is divided into 4 parts. All pieces needed for completion of the first part are already selected and can be seen in the tray, all unnecessary pieces disappear. You will be moved to the next part automatically only when you fully complete the first part.
To turn off the option and return to the full view please tap on the magnifying glass button again.