Digital Cinematography, 2nd Edition

170 Chapter 7

Any lens has two focal points, one on the object

side, called the primary focal point, and one on the

image side, called the secondary focal point. Defo-

cused object points are imaged as blur spots rather

than points. The greater the distance an object is

from the primary focal point, the greater the size

of the blur spot. Objects at greater distances from

the plane of lens focus can still appear sharp, and

the range of object distances over which objects

still appear acceptably sharp is referred to as the

depth of eld. The common criterion for accept-

able sharpness in the nal image is tha ...