Did you know that your Mac will zoom in on anything? This feature is available simply by holding down Control and using your scroll wheel. If you use a notebook computer, you substitute two fingerson your trackpad for the scroll wheel. Using this function, you can zoom in and out to your heart’s content. This feature comes in handy when trying to view small text or fine detail, or simply to give old tired eyes a break after a long day.
Source: “Quick Zoom with Your Mac” by Adam Pash, published at the LifeHacker blog, citing this post published at The Daring Fireball blog.