1. Mrs. Dornbach

2. The cornea allows light to enter the eye. As light passes through the eye the iris changes shape by expanding and letting more light through or constricting and letting less light through to change pupil size. The lens then changes shape to allow the accurate focusing of light on the retina. Light excites photoreceptors that eventually, through a chemical process, transmit nerve signals through the optic nerve to the brain. The brain processes these nerve impulses into sight. Diagrams & Information courtesy of health guide/howstuffworks.com

5. At f/2.8 only the focused subject will be sharp; foreground and background won't. With smaller apertures (f11) everything in the scene will be very sharp. Diagrams & Information courtesy of PhotoAficionado.com

6. The smaller the Number, (More light with narrow depth of field) The larger the Aperture. The larger the Number, (Less light with wide depth of field) The smaller the Aperture.