Depth of Field Study

This morning, I decided to do a study suggested in an article I read last night about understanding the concept of depth of field.

I set-up three objects (a LEGO box, a vase and a LEGO object) in a straight line, each about a foot apart, switched the camera to aperture priority (Av), dropped the f-stop value to the lowest setting (f/1.4), focused on the middle object (the vase) and took a picture. Then, I changed the f-stop to the next highest setting and took a picture, and continued until the maximum f-stop (f/22).

Below are three selections of the study: a low f-stop, a higher f-stop and a large f-stop.

	f/1.4: only the vase is in focus; the LEGO in the foreground and the writing on the label in the background is out-of-focus.
	f/2.2: a larger area around the base of the vase is in focus and more of the label in the background is in focus.
	f/18: the text in the label is readable and the LEGO piece in the foreground is in sharp focus.

Reviewing the series of photos, I observed that at the lowest f-stop only a small area around the focus-point was in sharp focus; the rest of the photo gots progressively blurry. As the f-stop increased, the amount of the photo that was in focus increased and the shutter-speed decreased (stayed open longer)— at f/22 the shutter speed was at 0.6s. I now have a better understanding of the relationship between the f-stop, the "bluriness" and the shutter speed.

(Aside: I think "depth-of-field" should really be called "area-of-bluriness".) Eric noted that digital cameras make it easy (i.e. inexpensive) to experiment like this and that an alternate name is "circle-of-confusion".