You can select the position and size of an area to zoom in on with Zoom To Rectangle.
Click the Zoom To Rectangle
button on the toolbar.
Choose View > Zoom > Zoom To Rectangle.
Press ⌘*
Select Zoom To Rectangle
.
The pointer changes to the Zoom To Rectangle pointer .
Drag a rectangle around the area you want to zoom in to.
Release the mouse to zoom in.
Zoom To Rectangle is automatically deselected after you have used it.