this is a good example of a photo having a narrow depth-of-field.
there are three (3) factors affecting depth of field:
- the diaphragm or aperture. in this photo, larger aperture (smaller number) was used in order to focus only a small part of the image.
- focal length. the smaller the focal length number of the lens, the greater the depth of field.
- distance to the subject. like in the photo, the closer you are to the subject,the smaller the DOF will be. while the farther you are from your subject, the greater the DOF will be.
source:
http://library.creativecow.net/articles/terry_todd/depth_of_field_converters/gnome-dof.JPG
