In case you haven't heard, Haile Gebrselassie rocked the running world this week by breaking 2:04 in the marathon. I say that he specifically rocked the running world rather than the entire world because when I found out that he had broken the record, I went the New York Times sports page to see what the would have to say about such a historic event. Not much apparently, as Gebrselassie's epic feat was featured at the bottom of the page with a stamp-sized thumbnail image, while the rest of the page was dominated by group of pudgy semi-athletes playing baseball for the last time at their stadium.

In any case, here’s shot of Gebrselassie just before his historic run. Now, this isn’t the most exciting picture from the race, but I’m using it because it does a good job of illustrating the photo concept I want to go over today: depth of field. Depth of field (DOF) referrers to how much of the scene is in focus in a picture. If the DOF is large, then almost everything in the picture will appear in focus, while if the DOF is small, then only a small amount of the scene will be sharp.

This picture of Gebrselassie, like most sports photos, uses a small DOF. The DOF is mainly dependant on the magnification of the subject (how big of a zoom lens you’re using) and the lens’ aperture (f-stop). The aperture of the lens refers to how big the hole letting light into the camera is. A large aperture (small f-stop number) lets in a lot of light and creates a small DOF, while a small aperture (large f-stop number) lets in a small amount of light and creates a large DOF.

So in the photo at the top of the page, Gebrselassie is in focus but the tower is very blurry because the photographer is using a large zoom lens (magnification of the subject) and a large aperture (a small f-stop number, like f2.8). Sports photography usually uses a small DOF because it makes the subject pop out from the blurry background, focusing the viewer’s attention on the action.

So there you have it, Haile is awesome, baseball sucks, and sports photography uses a small DOF!