This is a setting you can change - you can turn off the Auto-Zoom in the game settings, and it will stay at the same zoom level until you change it.

Astraware Mahjong does its best to move the board closer as you remove pairs of tiles. As you are left with fewer and fewer on the board it should automatically zoom in and the tiles should appear larger.

You can deliberately zoom in and out by putting two fingers on the screen and moving them together or apart to zoom out or in.

You can also swipe with just one finger to move the board from side to side (especially when you're zoomed in) to be able to see all the parts of the board.

We find that most players on a Tablet usually don't need to be able to zoom in to be able to play the game, but on some of the smaller phone devices, it becomes necessary in order to see the matching tiles a bit more clearly.