Configuring slideshows is easy, but controlling them while they run is even easier. Just move the pointer during a slideshow to show the hidden slideshow controls.
To run a saved slideshow:
Select the slideshow in the Source pane.
Click the Play button.
To control a slideshow:
To pause and restart the slideshow, click the Play/Pause button in the slideshow controls or press .
To move back and forth between slides, whether or not the slideshow is paused, click the left or right arrow button in the slideshow controls or press either (the left arrow key) or (the right arrow key).
Press (the up arrow key) to speed up the slide display time by one second per slide per keypress; press (the down arrow key) to slow it down by one second per slide per keypress.
To stop the slideshow, press any alphanumeric key or click the mouse.
The slideshow controls are a great help, but note that keyboard shortcuts for rotating, rating, and deleting photos also work during a slideshow, whether or not slideshow controls are showing.
If no photos are selected for a basic slideshow, iPhoto shows all the photos in the current album.
Although setting up and playing slideshows is easy, you can produce better results by keeping these tips in mind:
To avoid black edges (primarily with portrait-orientation photos) on monitors that don't use a 4 x 3 aspect ratio (such as most of Apple's flat-panel displays), either zoom in on photos or set the Scale Photos to Fill Screen option.
Avoid using images smaller than your screen (in pixels), since they will look jaggy when iPhoto scales them to fit.
If you really want to show small images, consider pasting them onto a larger background in a graphics program to increase their size and avoid iPhoto's scaling.
Remember that Macs can drive TVs via an S-video cable (you may have to buy it or an adapter separately). If you have a huge television handy, why not use that for a slideshow?
Another way of running a slideshow on a TV is to copy selected photos to your digital camera's memory card via a card reader and then display them via the camera, using its TV cable. Make sure to name the photos as your camera does and put them in the same location as the camera does to fool your camera into displaying them.
If you're playing the same slideshow continuously (at a party, for instance), select a large iTunes playlist to avoid repeating music.
If you have two monitors, slideshows appear on the one containing the iPhoto window.