use the tools to zoom in or out, pan let to right and get just the view you want . . .
Then press the DOWNLOAD button and place the selection box around the section you want, choose the resolution and BOOM they download you a closeup of the eye or whatever you've selected with the selection box.
I'm useing it to download a hi-rez of the eys right now. http://rapidfire.sci.gsfc.nasa.gov/fsi.php?Dennis.A2005190.1845.250m.jpg
This picture zoom-in link is a truly awesome link.
