If you need to zoom in on an image you're editing in iPhoto, there are a couple of ways to go about it. The most obvious method is to use the Zoom slider at the bottom of the window coupled with the small Navigation panel to move around in your magnified image.
I find, though, that it's much easier to use keyboard shortcuts. To do this, double-click on an image from your library to view it solo first, then place your cursor on the part of the picture that you'd like to magnify.
Press 1 to magnify the image by 100 percent, which'll center your zoom where your cursor was.
Press 2 to magnify by 200 percent.
That's a big ol' scary bunny eye!
To exit the magnification mode, use the Zoom slider pictured above, or tap 0 or Z to pull all the way back out.
Another important thing to know is that if your cursor is not hovering on your image when you press 1 or 2, iPhoto will zoom in on its exact center, which is handy.
And finally, you can use these shortcuts in other places around iPhoto, as well—press 0, 1, or 2 to quickly change how large your thumbnails appear in Events or Photos view, for example.
Pressing 0 makes the thumbnails as small as possible…
…while pressing 1 makes them as large as possible.
Pressing 2 makes them somewhere in between. Intuitive, right?
Now go forth and zoom your little hearts out, my friends. Your red-eye corrections will thank you.