Activate Zoom:           Click the Zoom icon on the bottom toolbar              

De-activate Zoom:    Click the Zoom icon again or the 'X' on the Zoom Control

Zoom Control

1. Move the zoom slider right to zoom in and left to zoom out
2. Change zoom focus by clicking your mouse at any point within the zoom thumbnail
3. Change zoom focus by holding down your left mouse button and moving the cursor within the zoom thumbnail

When the cursor is outside the Zoom Control thumbnail window
1. Use your mouse scroll button to zoom in or out
2. Change the cursor position to change the zoom focal point while scrolling in and out