Zooming on Gnome Shell can be done in many different ways, but here is the quickest and easiest way to do it whenever you need it!
First you will have to download this python script, and then you will have to make sure it runs on startup. Ubuntu users can simply add this ppa:tobias-quinn/gsmz on their own risk.
sudo add-apt-repository ppa:tobias-quinn/gsmz
sudo apt-get update
sudo apt-get install gnome-shell-mousewheel-zoom
Now you will need to restart Gnome Shell by pressing Alt+F2 and then “r” and Enter. Some of you may need to restart your operating system so that mousewheelzoom.py may run on startup.
After this you can zoom anywhere (desktop, windows etc) by pressing the left “Alt” + mouse wheel!