Open the Photo Organizer preferences dialog by going to Menu: Edit > Preferences > General. (see screen shot below)
Here I want you to uncheck the box "Allow photos to resize." This makes photos that are smaller than your screen fill the entire screen when using larger views. Having this enabled makes the photos look pixelated and ugly and does not give you a realistic view.
"Show File Names in Details" is another option you may wish to enable. I like to see the file names most of the time, and when I want more space for thumbnails, I can always turn off details right in the browser window.
