Research of depth of field (DOF) for capsule endoscope is important for the reason that the shapes of the
object plane of the intestine or the stomach are curve surfaces of "<" shape or "c" shape. The depth of field is
dependent on following factors: focal length, circle of confusion, aperture, and subject distance. The first
three factors are improved for wide view angle in prior paper and determined by the chosen sensor, and it is
not going against depth of field. Last factor, subject distance, is the more freedom to enlarge the depth of field.
However, depth of field is the range between near depth of field limit and far depth of field limit that are
acceptably sharp. The fraction of the depth of field behind the focus is always large then the one in front of
the focus distance. The depth of field does change with object distance, and it is increasing as object distance
is increasing. But the object distance of the design for capsule endoscope is short. The object distance setting
in front of the dorm is more efficient to use the depth of field than the one setting at the dome top. Therefore
there is an appropriate design of object distance to make depth of field be used efficiently to inspect curve
surface of intestine and stomach. The more vision information of inspect digestive system is get and is
compared easily to diagnose patients' condition under wide and efficient range of depth of field.