A normal photographic flash unit gives a flash that lasts around a thousandth of a second (a millisecond). However Alan's flash unit is much faster than this, and produces a flash of light around a microsecond (a millionth of a second). This allows him to freeze things that are happening extremely fast, and to give us a view of something that otherwise we would never see.
Check out the below gallery for a sample of these breathtaking images of exploding strawberries, glass ornaments, paintballs, tomatoes, crayons, walnuts and grapes.
Alan used an air rifle, a Nikon D40 camera and a homemade one-microsecond flash unit that cost around $300. For context, a typical camera flash is one-thousandth of a second, compared to the one-millionth of a second of this special flash unit. 
See more of Alan Sailer's work on his Flickr page.
